(22 June 2003)
Just after gravitational collapse of a massive stellar core, a newborn neutron star is formed. The matter inside a newborn neutron star has nearly constant entropy per particle of order 1-2 $k_B$ and lepton fraction of order 0.3-0.4. The properties of the neutron star matter, especially its equation of state, have a crucial role for studying the structure and evolution and also determining the mass of neutron stars. The stability of a neutron star depends on the value of adiabatic index.
In this work, we have calculated the equation of state of newborn neutron star matter and some of its properties such as temperature and adiabatic index over a wide range of density. For newborn neutron star matter, we have considered an electrically neutral composition of nucleons and leptons. We have observed that at high lepton fraction, the energy contribution from leptons dominates and equation of state of newborn neutron star matter is stiff. We have found that the tempertaure decreases by both decreasing entropy and increasing lepton fraction. We have seen that the adiabatic index increases by decreasing both entropy and lepton fraction.
It is suggested to interpret the non-thermal optical emission of rotation-powered pulsars as a spontaneous synchrotron re-emission of the secondary particles involved in the process of resonant absorption of pulsar radio emission. The resonant absorption takes place in the outer magnetosphere, where the radio waves meet the condition of cyclotron resonance. Although this process is not efficient enough to suppress the integrated radio luminosities considerably, it causes a substantial evolution of the momenta of absorbing particles. The synchrotron radiation of these particles is found to fall into the optical and higher-energy range. Because of strong variation of the particle momenta, the critical frequency of synchrotron radiation changes significantly inside the emitting volume. As a result, the spectra appear to be very flat over a wide frequency range. The model suggested is applicable for both the young and middle-aged pulsars, providing the optical luminosities up to $\sim 10^{34}\,{\rm erg\,s} ^{-1}$ and $\sim 10^{28}\,{\rm erg\,s}^{-1}$, respectively. In case of the Crab pulsar, one can explain the high-energy spectrum up to $\sim 10$ MeV.
The correlations between luminosities of radio pulsars in different ranges and magnetic fields at the light cylinder are discussed. They show that these emissions are generated in outer layers of pulsar magnetospheres and that the main mechanism of such generation is synchrotron one. The model is put forward to describe a formation of distribution functions of relativistic particles by quasi-linear interactions of waves excited by the cyclotron instability with particles of the primary beam and the secondary plasma. The formula is obtained for the calculation of X-ray luminosities L of radio pulsars. The high correlation between L and the parameter Pdot/P^3.5 is detected. It gives the possibility to predict a detection of X-ray emission from a number of known radio pulsars. The list of 114 such pulsars is given. Lorentz-factors of the secondary particles (1.5-8.5) calculated in the model suggest that magnetic fields at the surface of a neutron star in these objects are multipolar. Our model suggests that the majority of millisecond pulsars must be X-ray synchrotron sources. This conclusion differs from predictions of other models and can be used to test the considered model.
A new model is put forward to explain the main peculiarities of Anomalous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs). It is shown that a special mode of electromagnetic waves ("drift waves") can be generated in the vicinity of the light cylinder in the magnetosphere of a neutron star with magnetic field at the surface ~ 10^12 G. These waves cause a modulation of pulsar emission and appearance of pulses with periods of the drift waves P~10 s. In this model the rotation period of the neutron star (~0.1 s), its derivative (~10^ -13 s/s) and a small angle between the rotation axis and the magnetic moment (<10 degrees) can provide the possibility to describe the main properties of AXPs and SGRs.The rate of losses of the rotation energy of such stars (~10^37 erg/s) is sufficient to explain observed increasing of periods (~10^ -10 s/s), X-ray luminosities (~10^34 -10^36 erg/s) and ejection of relativistic particles into ambient supernova remnants. The rotation energy in our model can provide 10^4 gamma-bursts with the mean energy ~10^44 erg. Radio pulsars with periods >5 s are described probably by our model too.
Machabeli George Z, Malofeev Valeriy M
In recent years, there have been important developments in the determination of neutron star masses in binary systems. Whereas the best determination of masses in the range 1.3-1.4 solar mass is found for binary radio pulsars, limits on masses from measurements of kilohertz quasi-periodic oscillation frequencies in low mass X-ray binaries lie in the region of 2 solar mass. In addition several X-Ray binary masses have been found to be high (1.8 solar mass). These large masses put severe constraints on EOS of dense matter. We study the effect of quark and nuclear matter mixed phase on the mass-radius relation and on the radial oscillation modes of neutron stars. For this investigation we have considered two classes of EOS, namely the relativistic mean field theoretic models and recent models based on realistic nucleon-nucleon interactions incorporating relativistic corrections and three body nuclear interactions. For the quark phase we use the MIT model and the Nambu-Jona-Lasinio model. We find that the effect of mixed phase is to soften the EOS and to decrease the maximum mass of the stable star. The effect on radial oscillations is to cause a kink in the radial frequencies at the onset of the mixed phase.
Gupta Vijay K
Most of supernove remnants(SNRs) are radio ones. Using radio morphology, the galactic SNRs are divided into three classes: shell-like, crab-like or plerionic and mixed or composite. The shells dominate the total sample. It is particularly striking that these supernova remnants interacting with adjacent molecular clouds. It suggests that this interaction may play a role in the production of the maser emisiion at 1720MHz. The location of the masers, and the physical properties of the supernova remnant and the molecular cloud are consistent with a shock excitation model for the origin of the maser lines. We propose a new model of distinct thin circular disk shells to analyse the Gaussian fits to the spectral features of OH emission at 1720MHz toward the supernova remnant. CTA 37A is actually two supernova remnants with G348.5-0.0, a partial shell previously known as the jet, superposed on G348.5+0.1, a remnant with the characteristic breakout morphology(Frail et al. 1996,AJ, 111, 1651). We have obtained the OH(1720MHz) maser features toward G348.5+0.1 are radiated from three distinct thin circular disk shells. The parameters of the shells are obtained. The shells are related with excited shock wave fronts.
We discuss the controversial absorption features observed by the Konus detector in GRBs. The results that we have derived previously, in a radiation dispersion model for a relativistic moving plasma, have been employed. We note that the boosting on the resonance lines, produced in the emitting plasma of relativistic jets aligned with the line of sight, can provide the required shift on the lines, so that their positions fall into the observed frequencies in the range of ~ 20-60 keV. We show that this result can be taken as a strong argument in favor of the cyclotron nature of the observed absoption lines in GRBs.
On the other hand, we review briefly the large e+e- opacity problem in GRBs. It should be understood as a natural consequence of the ultra-relativistic motion of the emitting plasma and the beaming due to the special orientation of the jets pointing directly at us. We show that the observed flux radiation in Blazars (GRBs) strongly depends on the amount of relativistic beaming, as well as on the intrinsic properties of the jet.
We list a sample of 46 pairs of Pulsar (PSR) and Supernova Remnant (SNR) associations which have been suggested from over 230 SNRs and 1300 PSRs. At least half of them are still in active debate. We analyse factors which may result in the deficit of associations. Considering recent observational progress which suggests that PSR/SNR associations may be older than previously documented by an order of magnitude, that the characteristic age of a pulsar may be greatly different from its true age, and that a neutron star birth-place may be considerably offset from the geometrical centre of its associated SNR, we give a new sample of candidates for PSR/SNR associations. Comparing with previous searches for PSRs in SNRs or SNRs around PSRs, our sample includes some unconfirmed candidates. Pulsars with characteristic ages above 1000kyr are also removed from the sample.
Leahy Denis
It is reported on the detection of pulsed radio emission from X-ray pulsar J0205+6449 in the supernova remnant 3C58 and on results of the first investigations of this object. The observations were carried out using radio telescopes in Pushchino (BSA and DKR-1000) at frequencies 111 and 88 MHz. The period of the pulsar (is about 65.68 ms) and its derivation (P' = 1.9E-13 s/s) are confirmed. The integrated profiles at frequency 111 MHz are presented. The flux densities are measured. It is shown that the spectral index for the pulsar is about 3. Its dispersion measure is confirmed (DM = 141 pc cm-3). The problems of an evaluation of distances and ages for the system PSR - SNR are discussed. If the age of PSR J0205+6449 is equal to the age of 3C58 (820 years), this pulsar is the youngest one among all known radio pulsars. The synchrotron mechanism is used for the explanation of weaker radio and X-ray-emission of this pulsar comparing with the Crab pulsar which has many similar parameters. It is predicted that PSR J0205+6449 emits optical radiation with the luminosity Lopt is about 10E31 erg/sec and gamma-ray-emission with Lgamma is about 7E35 erg/sec.
Malofeev Valerij M, Malov Igor F, Glushak Alexander P
Regular high-precision timing of binary pulsars J0613-02, J1012+53, J1022+10, J1640+22, J1643-12, J1713+07, J2145-07 and pulsar B1937+21, in addition, is conducted at the Kalyazin radio telescope RT-64 (Russia) at 600 MHz over more than of 6 years. Large effective area of 64 m dish telescope and 160 channels receiver (40 kHz per channel) in dual circular orthogonal polarization ensure satisfactory signal to noise ratio to measure pulsar Time Of Arrival (TOA) of pulsars within accuracy about 1 ms. Several pulsars of the set have the orbital period more than 60 days and can be employed as good probes for gravitational wave background (GWB) test but other one, having a shorter orbital period, can be used for establishing a dynamic binary pulsar time (BPT) scale based on an ensemble of several reference pulsars. Upper limit of relative density of GWB is estimated less than 8.5E -4 at ultra-low frequency range from 1E -11 up to 7.1E-9 Hz . Pulsar timing observations at Kalyazin are in progress now.
Oreshko Vasilii V, Potapov Vladimir A, Rodin Alexandr E
We report on the progress of our search for highly dispersed pulsars near the Galactic Centre (GC) at 5 GHz using the 100m-radiotelescope in Effelsberg. This high frequency for a pulsar survey has been chosen as a compromise between the steep spectrum and the increased scattering of pulsar signals towards the GC by irregularities in the interstellar medium (ISM). We have observed the inner pointings of a ~0.2 deg^2 field centered to the GC with 1 hour integrations per pointing, thus reaching a minimum detectable flux density of 0.03 mJy at 5 GHz for normal period pulsars with a DM < 3000 pc/cc. The outer pointings in this field with an integration time of 36 min reach a flux density limit of 0.04 mJy. While no pulsar has been found up to now, this highly sensitive pulsar search provides new upper limits for ISM properties and statistics of pulsars in the GC. After the successful pilot search covering a small field along the northern Galactic has lead to the discovery of four pulsars, we present the key aspects of our new high latitude survey for millisecond pulsars at 21cm in the northern sky.
Kramer Michael , Mueller Peter , Wielebinski Richard
We report on our results based on 150 MHz observations of the millisecond pulsar J0437-4715 carried out using the Mauritius Radio Telescope (MRT). We discuss both the single-pulse and average properties, including also the possible effects of the interstellar medium on the measured decorrelation bandwidth. Our results are compared with those obtained at other frequencies. For the single-pulse properties, we also make use of data obtained at 327 MHz with the Ooty Radiotelscope.
Deshpande Avinash A
We have completed a search for radio pulsars using the Parkes 64 m telescope, covering approximately 4500 square degrees between 15 and 30 degrees from the galactic plane. Each pointing was observed for 265 s with the 13-beam multibeam system at a frequency of 1374 MHz. The signal from each beam was processed by a 96 channel filterbank and sampled every 125 microseconds, with a bandwidth of 288 MHz. This strategy affords rapid sky coverage and good sensitivity to pulsars with periods as short as 1 ms, whose existence would constrain the neutron star equation of state. Data were analyzed using the workstation cluster at the Swinburne Centre for Astrophysics and Supercomputing. This effort has yielded 25 new pulsars, including seven recycled pulsars. Taken together with the previous Swinburne Intermediate Latitude Pulsar Survey, a total of 94 new pulsars were found over nearly 7500 square degrees of sky between 5 and 30 degrees from the plane of the galaxy. This large sample of newly discovered objects contains no young pulsars.
The timing stability in a long term for some millisecond pulsars becomes competitive with terrestrial atomic clocks. Long term timing of multi-millisecond pulsars can contribute to study of an ensemble pulsar time scale PTens. Wavelet decomposition algorithm (WDA) was appled to define a PTens using the aveilable milisecond pulsar timing data. The PTens obtained from WDA is more stable than results from other algorithm. As many millisecond pulsars were newly discovered, timing multi-millisecond pulsars using one radio telescope becomes reality. Chinese 50 m radio telescope is specially designed for PTens study and detection of gravitational wave background by millisecond pulsars timing observations. A scheme for multi-millisecond pulsar timing and ensemble pulsar time study is discussed in some details. The observations of a number of millisecond pulsars distributed across the sky lead to the possibility of timing several pulsars against each other without ultimate reference to terrestrial clocks.
Ni Guangren
We use Monte Carlo techniques to simulate the statistical properties of rotation-powered pulsars in the Milky Way. The gamma-ray properties of these pulsars are calculated by using a self-consistent outer gap model and other pulsar properties, i.e. initial magnetic field and period, and velocity distribution of the neutrons stars at birth, are obtained from the statistics of radio pulsars. We obtain distributions of the magnetic field, period, spatial, age, and gamma-ray flux for these gamma-ray pulsars in the Milky. We compare the model statistical distributions, i.e. spatial, spectral index, gamma-ray flux and log N-log S, with those statistical properties of unidentified gamma-ray sources detected by EGRET and find some similarities between these two groups. Our preliminary results indicate that those unidentified gamma-ray sources associated with the pulsars in the galactic plane should have period between 0.1-0.3s and their typical age is around 3 hundred thousand years old. However, those unidentified sources associated with gamma-ray pulsars in the Gould Belt,which are very much above the galactic plane, have period 0.5-0.8s and their typical age is near one million year old.
Cheng K.S. , Zhang L.
We have made a Chandra catalog of supernova remnants ("http://hea-www.harvard.edu/CHANDRASNR"). The catalog is intended to present data useful in proposal preparation as well as in studies of the properties of supernova remnants. We have extracted the regions containing each remnant from cleaned Chandra ACIS and HRC fields that are in the public archive. Images in selected X-ray energy bands and at other wavelength are all presented to the same scale. Some are smoothed to better visualize faint features. A three-color image illustrates spectral differences. Pulse height spectra are given for remnants as a whole and for selected features which vary from remnant to remnant. Tables give count rates, fluxes, and luminosities of remnants, and positions of serendipitous sources in the fields. Distances (from the literature) and column densities (from spectral models) used to derive luminosities are included. For each remnant there is a downloadable event file and various images in FITS,PS, and JPG formats. Most data were taken with the ACIS instrument which has a field-of-view of 8'x8' or 16'x16'. Although somtimes it has been possible to combine several fields into a mosaic, the larger remnants are generally only partially observed.
Seward Frederick D, Slane Patrick O, Smith Randall K, Gaetz Terrance J, Lee Jae-joon
We report on the intensity variations of PSR B1642-03 at 1.7 and 2.3 GHz. The flux densities of the integrated pulse profiles ocassionally go up by more than a factor of 40 over it's mean value. No such large variations have been observed on the rest of the pulsars in our sample. This pulsar was recently reported to be undergoing free precession (Shabanova, Lyne & Urama, 2001). Some implications of the temporal flux changes are discussed.
PSR B1828-11 have long-term, highly periodic and correlated variations pulse shape and of the rate of slow-down with period variations approximately 1000, 500 and 250 days (Stairs et al., 2000). There are three potential explanations of time of arrival pulses from pulsar concerned with the interior of the neutron star, planetary bodies and free precession. The rotation of the terrestrial planets having rigid mantle and elliptical liquid core is characterized by Free Core Nutation (FCN). We use the Hamiltonian canonical technique of Getino (1997) for dynamically symmetrical pulsar composed of the rigid crust and elliptical liquid mantle. Correctly extending theory of core-mantle differential rotation of planet, we have obtained the periods of $P_{CW}$ and $P_{FCN}$ for different pulsars in second approximation. We investigated dependence of period CW and FCN from the state equation of neutron liquid, flatness of mantle and crust of the neutron star. Detection the Chandler Wobble (CW) and FCN of the pulsar and its periods allow: to determine mantle and core radius and its flattening; to determine density jump at the Crust-Mantle Boundary and Core-Mantle Boundary.
Kitiashvili Irina
At present time is known approximately 750 radiopulsars, from them 27 pulsars is observed in other bands and only seven are observed in the optical band. Discovery exoplanets around PSR~B1257+12 and PSR~B1828--11 gave strong push for search and investigation of planets around neutron stars. At the early stages of planet evolution the tidal and magnetic interactions of exoplanet with disk takes a principal role: the tidal effects lead to the capture into resonance rotation of the planet, the analyses of gravi-magnetic interaction has shown that a direct rotation of the planet may be passed into reverse rotation and vice versa for a rather broad range of the parameters. The dynamical structure of protoplanetary disk are reviewed. Investigation of protoplanetary disk around the optic pulsar by VLTI for combination of observed periodic delays in the arrival times of pulsar pulses are proposed. Measurements of the near-IR sizes of the central regions of the young neutron stars, with high-resolution interferometric studies of protoplanetary disks should help clarify how disk structure affects formation and migration of exoplanet.
Gusev Alexander
A detailed timing analysis of the data from a 4.5 year RXTE monitoring of the Anomalous X-ray Pulsar (AXP) 1RXS J170849.0-400910 is presented. A sudden spin-up event in this source was already detected and, when interpreted in terms of a radio pulsar-like glitch, this event lends further support to the magnetar model for AXPs. We present the detection of a new and larger glitch and illustrate the peculiar behaviour of the post-glitch recoveries of both glitches; their interpretation in the framework of glitch models is outlined. Moreover, different interpretations of the spin-up events will be discussed, along with their possible implications on the nature of AXPs.
Israel Gianluca , Stella Luigi
Monthly flux monitoring at 5 GHz are reported for the pulsar B0329+54. We have observed this pulsar during one year using the Toru? 32-m Radio Telescope. Typical observations lasted 24 hours, in 3 minutes scans. This pulsar shows a very strong variations of the flux-density at 5 GHz, from a few mJy to 200 mJy during the whole day. The average values from monthly observations vary not so much and are consistent with spectrum of this pulsar. We also present 24 hours flux measurements at 5 GHz for three other pulsars: B0355+54, B0540+23 and B2021+51.
Gupta Yashwant , Krzeszowski Krzysztof , Lewandowski Wojciech
Spectra of several pulsars with turnover at unusually high frequencies ~ 1 GHz are presented. There are relatively young pulsars with DM typicaly larger than in pulsars showing a low-frequency turnover.
Maron Olaf
The pulsar catalogue system used for many years by a number of research groups around the world has been upgraded. First, the catalogue database has been extended to include the most recent data on more than 1400 pulsars with full bibliographic information for all entries. Second, a new web-based interface for the catalogue has been developed. This permits tabulation and plotting of selected parameters in a variety of formats. Pulsars may be selected according to logical conditions on parameter expressions, radial distance from a nominated position, or pulsar name(s) with wild-card specifications supported. Custom parameters may be defined with standard mathematical expressions supported. The web interface has two modes of operation, normal and expert. Expert mode supports more parameters and custom databases. The catalogue can also be accessed from the command-line interface.
Hobbs George , Teoh Albert , Hobbs Maryam
We have developed a 3D magnetospheric simulation of co-rotating dipole magnetic field embedded in a relativistic plasma. A model for the coherent radio emission is developed, and investigated the role of rotation on pulse properties. The model predicts the physical conditions which are conducive for the generation of pulse components at different altitudes. We find the inner components including the core are emitted at lower altitudes while the outer components are emitted at higher altitudes. Further, rotation broadens the width of leading component compared to the width of trailing component of a cone due to aberration and retardation. The inclination between the rotation and magnetic axes can introduce an asymmetry in the circular polarization of the conal components, which has been observed in most of the pulsars. We have analyzed the single pulse polarization data of PSR B0525+21 at 606 MHz, and found that in conal components one sense of circular polarization dominates in the leading component while the other sense dominates in the trailing.
We have calculated the evolution of neutron stars surrounded by a supernova fallback disk, with an improved estimate of the torque exerted by the disk and the time dependence of the mass transfer rate. We show that for reasonable distributions of its free parameters, the disk model is unable to produce any anomalous X-ray pulsars as observed - the influence of the fallback disk on neutron star evolution was overestimated. Based on the calculated results we also critically comment on the fossil disk proposed recently for young radio pulsars.
The thermal evolution of Neutron Stars with internal heating admits the existence of Neutron superfluid layer and the posibilty that may cool much faster than through "standard" scenario. However in standard calculation of the cooling time, the possibility of the heat propagation by waves is obviated. This simplification will be spurious in the degenerates material because the relaxation time (the time requerideed for to establishment the heat flux when one temperature gradiend is switched on)is not neglecting. Neutron Stars cooling theory is revised before the thermal relaxation. The existence of the layer interior superfluid in NS facilitates the propagation of the heat waves, mainly during initial transcient of the duration in order of relaxation time, which occured at the birth of the NS. Using the Cattaneo law for the heat flux,it is shown changes in the energy transport equation and insinuates quasiperiodic pulses in the luminosity. The cooling theory based in the causal law (Cattaneo law) predicts that the energy is spring up by heat waves and the cooling time could be most short. Applications in single NS oscillators and pulsars are suggested.
The effects of an electromagnetic torque on spherically symmetric, axisymmetric and asymmetric pulsars is studied. The near-field produces precession of a kind distinct from the familiar free precession that results from asymmetries in the mass distribution. Its effect on timing residuals is analysed numerically. The model also includes a rotational diffusion constant in the equations of motion to account for the energy loss due to the intrinsically stochastic nature of the electromagnetic torque.
Frescura Fabio A
The electromagnetic fields of magnetodipole radiation can penetrate to the conducting matter of the neutron star crust and create there the electric currents and the tangential magnetic field of high magnitude. The obtained solution has the form of surface of magnetic field discontinues propagating through the crust to the core. This model explains the phenomena of Magnetars - Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars.
Forty different VLA pointings have been combined using mosaic techniques to produce a new, high-quality radio image of the galactic SNR Puppis A at 1.4 GHz. This mosaic makes an impressive map of Puppis A for comparison with the X-ray images. The new observations are combined with previous lower frequencies images of Puppis A, to carry out a detailed study of spatial variations of the spectral index, particularly in the environs of the associated radio-quiet neutron star RX J0822-4300. Local variations in the radio spectral index reflect changes in the average energy distribution amongst accelerated elctrons. The identification of such variations in the spectral index allow us not only the recognition of distinct components in the SNR, but also to analize the influence of inhomogeneities in the acceleration mechanisms.
Goss W. M, Castelletti Gabriela M, Reynoso Estela M
CTB 80 is a complex supernova remnant (SNR) consisting of three extended arms with a remarkable pulsar wind nebula (PWN) in the center. New high resolution observations of the whole SNR have been carried out at 240 MHz (beam ~ 20") and at 618 MHz (beam ~ 8") using the Giant Metrewave Radio Telescope (Pune, INDIA), and at 324 MHz (beam ~ 65") and at 1380 MHz (beam ~ 80") using the VLA (NRAO, Socorro-NM, USA). These new high quality radio images have disclosed previously unknown structures in the PWN. In addition, the high dynamic range attained, permits the identification of faint features in the extended arms that accurately correlate with the optical and infrared emission. On the basis of the present multiwavelength observations, it has been carried out a detailed study of the spatial variations of the spectral index. The results suggest the presence of flat spectrum components beyond the PWN, mainly aligned with the nothern SNR arm.
Dubner Gloria M, Golap Kumar , Goss W. M, Velazquez Pablo F
Giant pulses, occasional individual pulses with an intensity at least 10 times more but typically 100 times the average intensity, have been detected in three pulsars (B0531+21, B1937+21, B1821-24) todate. Their origin is not well understood, but studies suggest a connection between the strength of magnetic field at the light cylinder and the existence of giant pulses. Since millisecond pulsars (MSPs) often tend to have a larger light cylinder magnetic field, giant pulses should be, on an average, more likely to be seen in MSPs. Here, we report on observations of a sample of 7 pulsars selected in order to test the above conjecture and discuss our results. We also report on high sensitivity observations of individual pulses in the Crab pulsar (B0531+21) probing both the normal and giant pulse intensity distribution.
Kramer Michael , Lyne Andrew , Mclaughlin Maura , Stairs Ingrid
The Be/X-ray binaries represent the largest subclass of high-mass X-ray binaries. These systems consist of a Be star with an equatorial disk and, generally, a neutron star. Most of the Be/X-ray binaries show only transient X-ray activity as a result of transient accretion onto the neutron star from the Be-star disk. Rencently, Okazaki et al.(2002) studied the interaction between the Be-star disk and the neutron star, using a 3D SPH code. In their simulations, however, the neutron star was modeled by a sink particle with the size of the Roche lobe, so no direct comparison with the observed X-ray data was possible.
In this paper, we study the accretion onto the neutron star in Be/X-ray binaries, using the 3D SPH code and the data from the simulations by Okazaki et al.(2002). We find that a non-steady accretion disk is formed around the neutron star. While the mass-capture rate by the neutron star has a regular, strong dependence on the orbital phase, the orbital modulation in the accretion rate at the inner simulation boundary slowly gets damped. Our simulations show that the truncated disk model for Be/X-ray binaries is consistent with the observed X-ray behavior.
Okazaki Atsuo T
We present results of the simulation of the core collapse of the rotating magnetized presupernova star. We use equation of state for very high densties and temperatures and take into account neutrino losses. We show that collapse and differential rotation in the star lead to the amplification of the toroidal magnetic feild and following ejection of the part of the envelope of the star. Our simulations show that magnetorotational mechanism for supernova explosion is effective in 2D approach.
We study the coherent curvature radiation generated by a charged particle moving in the plasma along the curved magnetic field. We have shown that although the plasma partially screens the radiation process, the emitted power is still enough to provide the sufficient energy for the pulsar radio emission. We estimate the number, size and charge of the bunches necessary to obtain observed power.
Luybarskii Yuri , Gil Janusz
We present a new mechanism for generation of pulsar radio emission, based on the excitation of mixed electrostatic-electromagnetic lt-waves in the non-stationary plasma of pulsar magnetospheres. As shown by Asseo & Melikidze (1998), the
Melikidze George
From the observations of SN1987A, radio active elements around the core, i.e., young neutron star, is expected well mixed into surrounding envelope. These debris of young neutron star is assumed to be mixed by Rayleigh-Taylor (RT) Instability and to result in clumps of heavy elements in the supernova remnant. By observing the widths of spectral lines of heavy elements at infrared, Witteborn found that expansion velocities of heavy elements were 3000--4000km/s in the expanding envelope of SN1987A. Many numerical studies of RT instability in the envelope so for studied have failed to reproduce observed high velocities. We perform a parameter survey of the growth simulation of RT instability with Adaptive Mesh Refinement Scheme performed in 3D space with higher resolution. We demonstrated the formation of clumps of radio active elements and set a restriction on presupernova model.
Ogawa Tomoya , Miyaji Shigeki , Yamashita Kazuyuki , Den Mitue
A coherent pulsar dedispersor is being built at Nancay Radio Observatory in collaboration with the University of California, Berkeley. Analog crates and D/A converters from the NBPP (Navy Berkeley Pulsar Processor) are being presently used to provide 4 bits voltage data to a cluster of computers dedicated to remove the disturbing dispersion introduced by the ionized ISM. This process is done in real-time for a total bandwidth of 55MHz at 1.4GHz.
Description of the instrumentation, first results obtained for a set of normal and millisecond pulsars and prospective for the future will be presented.
Backer Don C, Ramachandran R
Transient X-ray emission, with an approximate t^{-0.7} decay, was observed from SGR 1900+14 over 40 days following the giant flare of 27 Aug 1998. We calculate in detail the diffusion of heat to the surface of a neutron star through an intense 10^{14}--10^{15} G magnetic field, following the release of magnetic energy in its outer layer. We show that the power law index, the fraction of burst energy in the afterglow, and the return to persistent emission can all be understood if the star is composed of normal barionic material.
Eichler David , Thompson Christofer
Both nulling and subpulse drifting are poorly understood phenomena. We probe their mechanisms by investigating how they interact in PSR B0809+74. We solve the subpulse alias-order problem and show that the apparent drift of the subpulses directly reflects the actual motion of the subbeams at the pulsar. From this we derive a subbeam-carousel rotation time of more than 200 seconds, much longer than predicted by theory.
We find that after nulls the drift pattern is different from normal, sometimes stably so for up to 150 seconds. The most striking change is the large decrease in driftrate. With the alias mode known, we can now tie these drift-pattern changes to changes in emission-region geometry. We show that the post-null emission originates deeper in the pulsar magnetosphere. Both this emission-height change and the striking increase in carousel rotation time (seen as the driftrate decrease) can be explained if the gap height is less after a null. This offers a glance at the circumstances needed to make the pulsar turn off so dramatically.
Stappers B.w. , Ramachandran R. , Rankin J.m.
The magnetic field strengths of most millisecond pulsars(MSP) are about 10**(8-9) Gauss, and the MSPs with the fields of several 10**(7) Gauss have not yet been detected. The proposed magnetic field evolution of neutron star considered the accretion flow in the binary system to be the main reason to account for the field decay. If little mass accreted, such as in the High Mass X-ray Binary system, the field decays not so much. However, at the last stage of Low mass X-ray Binary system, the field decays to about 10**(8) Gauss, if half solar mass matter accreted from the companion. Furthermore, the magnetic field evolution stops at the saturated value of about 10**(8) Gauss, where the magnetosphere of the star is compressed onto the surface of the neutron star, so the field is little influenced at this stage even though the extra mass is accreted. The homogeneous distribution of MSPs in fields and periods would imply the homogeneous properties of their late evolution stages in the X-ray binary phases, which links the detected X-ray sources, such as Atoll sources and Z sources.
The state of the art of optical studies of pulsars and isolated neutron stars is reviewed. In addition, results obtained from recent HST and VLT observations of pulsars and their environments are presented.
Mignani Roberto , Deluca Andrea , Caraveo Patrizia
Recent progress in the analysis of drifting subpulses in pulsars provided strong support to Ruderman & Sutherland model by revealing a number of subbeams circulating around the magnetic axis in a period roughly comparable with theoretical predictions. However, more detailed analysis revealed also that the model value of circulation speed in a pure vacuum gap is much too high when compared with observations. Moreover, some pulsars often demonstrate significant time variations of the drift rate, including a change of the apparent drift direction, which is obviously inconsistent with the ExB drift scenario. We attempted to resolve these discrepancies by considering a partial flow of iron ions from the polar cap surface, coexisting with the production of outflowing electron-positron plasmas. The model of such charge-depleted acceleration region is highly sensitive to both the critical ion temperature (above which ions flow freely with the corotational charge density) and the actual surface temperature heated by bombardment of ultra-relativistic charged particles. By fitting theoretical ExB drift-rates to observationally deduced values, we managed to estimate polar cap surface temperatures in a number of pulsars.
Geppert Ulrich , Melikidze George
Stochastic growth theory (SGT) assumes that the plasma source has evolved to a dynamic equilibrium near marginal stability. In the absence of any nonlinear emission mechanisms, SGT predicts that the probability distribution function (pdf) of the wave field and intensity I are lognormal. In this work SGT predictions for the pdf of the Stokes parameters are presented and compared to pulsar data. Probability density functions for the observable Stokes parameters Q and V are found from the the pdf of I , and the pdf of the mixing angle, which describes the mix of left and right circularly polarized transverse waves. The pdf of the mixing angle is modeled with a uniform or Gaussian distribution. The pdf's of Q and V are formed, and analytic expressions presented for the moments, asymptotic limits and peaks of the pdf, thus providing expressions for convenient comparison with data. In the absence of polarity-dependent propagation effects, the analysis thus relates the observable quantities to the polarization statistics of the source plasma. Polarity-resolved pulsar data is compared with the predictions of SGT.
Robinson Peter A, Cairns Iver H
We are currently analysing the timing residuals for more than 350 pulsars for which we have between six and 35 years of timing data. The aim of this project is to obtain the first-ever analysis of pulsar timing residuals with a large sample of pulsars and with long time spans. The poster contains details of the background to this work as well as some initial results such as a description of the different structures observed in the timing residuals. Correlations between the amplitude and `time-scale' of the timing noise and standard pulsar observed and derived parameters are also given.
Lyne Andrew , Kramer Michael
The Cygnus Loop is one of the nearest supernova remnants (440pc) and has been studied extensively in radio through X-ray wavelengths. An unusual bright V-shaped region on the south-western limb (near RA 20h46m and dec.+30.0deg) was revealed in ROSAT PSPC observations of the Cygnus Loop (Aschenbach and Leahy 1999 A&A, 341, 602). The left side of the V has one of the highest hardness ratios (0.9-2keV/0.1-0.4 keV) in the Cygnus Loop whereas the right side has one of the lowest. Images and spatially resolved spectra were obtained using Chandra ACIS observations. The results of analysis of the images and spectra are presented and the nature of the V is discussed.
This work supported by the Natural Sciences and Engineering Research Council of Canada.
CTA 1 is a shell-type radio SNR whose X-ray spectrum and morphology reveal a central synchrotron nebula. At the center of the nebula lies RX J0007.0+7303, a faint point source that appears to be the likely pulsar that drives the system. The source is located within the error box of the EGRET source 3EG J0010+7309 and is a strong candidate for the counterpart. Here we report on ASCA and XMM observations of the central source and surrounding wind nebula, including a search for pulsations, a characterization of the nebular spectrum, and a search for thermal emission from the SNR shell.
This work has been supported in part by NASA Contract NAS8-39073 and Grants NAG5-4803 and NAG5-10017.
Zimmerman Erik R, Clarke Melanie J, Gaensler Bryan M, Hughes John P
1E 1841-045 is an Anomalous X-ray Pulsar that lies at the center of the young supernova remnant Kes 73. The AXP emission is well described by a model consisting of a blackbody and a power law spectrum, typical of other such sources. Using Chandra data, we have explored spectral models which include the effects of a highly magnetized atmosphere. Using continuous-clocking data, we detect the 11.8 s pulsations and investigate the spectrum as a function of phase. We contrast the lack of strong spectral variability as well as the observed pulsed fraction, and its energy dependence, with models for the emission from AXPs.
This study is supported in part by NASA Contract NAS8-39073 and Chandra grant GO0-1118X.
Hughes John P, Ozel Feryal
The complexity of pulsar emission is manifested perfectly in the characteristics of the individual pulses. We have conducted simultaneous observations of single pulses from the bright pulsars B0329+54 and B1133+16 at two frequencies in full polarisation and a total of four frequencies in total power only. Our aim is to investigate the frequency dependence of the pulse properties on timescales of a pulse period. Our total power analysis, ranging from 238 MHz to 4.85 GHz, shows that total power emission remains well correlated across the observed frequencies and that the spectral indeces of the individual pulses follow the measured mean spectral indeces, even in individual pulse components. In the case of PSR B1133+16, we find and discuss a correlation between the measured spectral index and the flux density in the single pulses. A polarimetric analysis has also been performed on dual-frequency data (1.41 GHz - 4.85 GHz) to investigate the Orthogonal Polarization Mode phenomenon. We unveil strong correlations in the polarization between the observed frequencies. The correlation in frequency, however, is not perfect both for the polarization position angle and the circular polarization, indicating a frequency dependent mechanism affecting the radiation, such as propagation effects through the pulsar magnetosphere.
Johnston SImon , Kramer Michael , Bhat Ramesh , Gupta Yashwant
Precise timing of the millisecond pulsar B1937+21 was made jointly under Russia - Japan agreement by using Kalyazin 64 m dish radio telescope (Physical Lebedev Institute, Russia) and Kashima 34 m one (CRL, Japan) in more than 5 years. At Kalyazin timing were conducted by 0.6 GHz filter bank receiver with 3.2 MHz bandwidth (two polarizations). At Kashima timing were performed by 2.2 GHz acousto - optical receiver with 200 MHz bandwidth. An accuracy of measurements of Time of Arrival (TOA) pulses of pulsar was within several hundreds of ns on both radio telescopes. Local time scales of radio telescopes were under GPS monitoring. Topocentrical TOA sets of both telescopes were transformed to the solar barycenter, and pulsar parameters were fitted by both TIMAPR and TEMPO package. Total set of barycentrical residuals (RES) have been found out to have RMS through all span no more than 2.1 ms and is not seen any systematic trends of RES on these level. It can be accounted to millisecond pulsar B1937+21 that it has a satisfactory long- term stability and therefore it can be considered as the independent reference precise clock for Pulsar Time scale.
Imae Michito , Hanado Yuko , Oreshko Vasilii V, Potapov Vladimir A, Rodin Alexsandr E, Sekido Mamoru
The fundamental properties of neutron stars provide a direct test of the equation of state of cold nuclear matter. The most straightforward method of determining these properties is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere, as this redshift provides a direct constraint on the mass-to-radius ratio. We report the discovery of significant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO 0748-676. We identify the most significant features with the Fe XXVI and XXV n = 2-3 and O VIII n = 1-2 transitions, all with a redshift of z = 0.35, identical within small uncertainties for the respective transitions. For an astrophysically plausible range of masses (M ~ 1.3 - 2.0 solar masses), this value is completely consistent with models of neutron stars composed of normal nuclear matter, while it excludes some models in which the neutron stars are made of more exotic matter. We discuss the possibility of using the profile of these lines to measure both mass and radius of the neutron star, independent of other system parameters.
Cottam Jean , Paerels Frits
We present a detailed radio study of the young supernova remnant (SNR) G292.0+1.8 and its associated pulsar PSR J1124-5916 using the Australia Telescope Compact Array. We find that the radio morphology of the source consists of three main components: a polarized flat-spectrum central core coincident with PSR J1124-5916, a surrounding circular steep-spectrum plateau with sharp outer edges and, superimposed on the plateau, a series of radial filaments with spectra significantly flatter than their surroundings. The core clearly corresponds to radio emission from a pulsar wind nebula powered by PSR J1124-5916, while we conclude that the plateau represents the surrounding SNR shell. The plateau's sharp outer rim delineates the SNR's forward shock, while the thickness of the plateau region demonstrates that the forward and reverse shocks are well-separated. We interpret the flat-spectrum radial filaments superimposed on the steeper-spectrum plateau as Rayleigh-Taylor unstable regions between the forward and reverse shocks of the SNR. The flat radio spectrum seen for these features results from efficient second-order Fermi acceleration in strongly amplified magnetic fields.
Wallace Bradley J
G357.7-0.1 ("the Tornado") is an unusual radio source whose morphology defies classification. It has been proposed at various times that the Tornado is powered by a central pulsar, is an exotic accreting system, or is a supernova remnant with a distorted morphology, any one of which could generate the radio emission seen from this source. We here report on the conclusive detection of X-ray emission from the Tornado, using observations with the Chandra X-ray Observatory. We will describe the morphology and spectrum of this emission, and will discuss the implications for the interpretation and structure of the Tornado. This work has been carried out with the support of NASA through SAO grant GO2-3041X.
Fogel Jeffrey K, Slane Patrick O, Eikenberry Stephen S, Wijnands Rudy A, Miller Jon M, Lewin Walter H
Pulsars with ages in the range ~10,000-20,000 years (the "Vela-like pulsars") tend to be complex sources of X-ray emission, because of potential contributions from each of the neutron star surface, the pulsar magnetosphere and a surrounding synchrotron nebula. Observations which simultaneously provide high spatial, spectral and temporal resolution are needed to disentangle all these sources of X-ray emission and thus interpret these systems. We here present a 25-ks XMM-Newton observation of PSR B1046-58, a Vela-like pulsar with a spin period of 124 ms, a characteristic age of 20,000 years, a spin-down luminosity of 2.0 x 10^36 erg/s, and a possible association with the EGRET source 3EG J1048-5840. Our previous ASCA observations showed a complex region of X-ray emission at this position, possibly corresponding to several sources. The new XMM data presented here confirm this interpretation, and allow us to identify an extended source at the position of PSR B1046-58 which we interpret as an associated pulsar wind nebula. This work has been carried out with the support of NASA through XMM-Newton Guest Observer grant NAG5-11376.
Pivovaroff Michael J, Schulz Norbert S, Kaspi Victoria M, Becker Werner E
We investigate the transition of nuclear matter to strange quark matter (SQM) inside neutron stars (NSs). It is shown that the influence of the magnetic field expected to be present in NS interiors has a dramatic effect on the propagation of a laminar deflagration (widely studied so far), generating a strong acceleration of the flame in the polar direction. This results in a strong asymmetry in the geometry of the just formed core of hot SQM which resembles a cylinder orientated in the direction of the magnetic poles of the NS. This geometrical asymmetry gives rise to a bipolar emission of the thermal neutrino-antineutrino pairs produced in the process of SQM formation. The $\nu {\bar \nu}$ annihilate into $e^+ e^-$ pairs just above the polar caps of the NS giving rise to a relativistic fireball, thus providing a suitable form of energy transport and conversion to $\gamma$-emission that may be associated to short gamma ray bursts (GRBs). We find that moderate magnetic fields ~ $10^{13}$ G will originate a prompt beamed GRB with energy $E > 10^{51}$ erg which will last for ~0.2 sec.
Lugones German , Ghezzi Cristian R, Horvath Jorge E
We present new high radio frequency data of the Boomerang pulsar wind nebula observed with the 100-m radio telescope in Effelsberg. A comparison with low frequency data from the Canadian Galactic Plane Survey reveals a change of the nebula's emission structure with frequency caused by a radial steepening of the radio spectrum above 5 GHz. We also found evidence that the reverse shock of the initial supernova shock wave drove away or crushed the original pulsar wind nebula which might explain why the current nebula around the pulsar has such a low radio luminosity.
Uyaniker Bülent , Reich Wolfgang
PSR B1259-63 is a young pulsar in a highly eccentric orbit about a 10 solar mass B2e star. It was discovered in 1990 and has been regularly observed ever since. The pulsar has completed 4 orbits since its discovery, including periastron passages in 1991, 1994, 1997 and 2000. The orbit appears to precess due to spin-orbit coupling and the disk of the Be star is highly inclined with respect to the orbital plane. We present 13 years of timing observations of the pulsar and discuss the implications of the results for its past and future evolution.
Johnston Simon , Manchester Richard
The equation of motion of a superfluid vortex includes a self-induced component, as well as terms describing normal fluid friction and the Magnus force, in the local induction approximation. We integrate the equations of motion of an ensemble of vortices in a spherical, Taylor-Couette geometry, starting from a regular array parallel to the rotation axis. The conditions for the onset of a vortex tangle are determined, as is the form of the effective mutual friction force in the hydrodynamic Hall-Vinen-Bekharevich-Khalatnikov equations describing the flow of a 1S0 superfluid. The results are applied to unmagnetized vortex pinning in young (Crab-like) and adolescent (Vela-like) pulsars.
Melatos Andrew
We compute the distorted hydromagnetic structure of a neutron star accreting spherically or at its poles as a function of accreted mass Ma, by evolving an initial dipole through a quasistatic sequence of Grad-Shafranov equilibria, and investigate the structure of the resulting magnetic mountain. Our calculation is the first to (i) follow the development of high-order multipoles due to equatorial hydromagnetic spreading, and (ii) maintain strict flux freezing between the initial and final states. We find that Ma > 10^-5 Msun is required to significantly distort the field, higher than previous estimates (10^-10 Msun), and that buoyant magnetic bubbles can form when the distortion is severe. The results are applied to newly born neutron stars (experiencing post-supernova fallback) and magnetars (testing the fossil disk hypothesis for AXPs).
Melatos Andrew
Many neutron stars have been detected as radio pulsars. Recently, several X-rays point sources with no radio counterpart have been detected near the centre of supernova remnants (SNRs). In most cases, these sources were claimed to be the neutron stars left behind after the supernova explosions. One of these compact sources, 1E 1207.4-5209, was found to lie at the centre of an HI depression, raising the question of whether the hot atmosphere of the neutron star heated up the neighbouring gas and produced the observed depression. The coincidence between the systemic velocity of the small hole and of larger-scale structures interacting with the SNR's shell, allowed the authors to conclude that both the SNR and the neutron star were associated. We present the results of a search for similar traces in the interstellar gas undertaken with the VLA and the ATCA towards a sample unresolved X-ray sources, located both in the center of SNRs and in isolation.
Green Anne J, Johnston Simon , Goss Miller , Dubner Gloria M, Giacani Elsa B
A study of the nature and the spatial distribution of over 250 discrete radio sources (HII regions and SNRs) in the Magellanic Clouds (MCs) is underway. A multi-frequency comparison of these sources involves the latest radio, IR, optical and X-ray surveys with angular resolution of <1 arcmin. Special emphasis is given to the MC SNRs. Their morphology, birth rate and overall properties are investigated and compared with Galactic SNRs and SNRs from other nearby galaxies. Also, we are investigating the radio source distribution throughout both MCs.
The Parkes-MIT-NRA0 (PMN) survey was used to study Galactic SNRs at the frequency of 4.85 GHz. We present flux density values for 121 Southern Galactic SNRs observed with Parkes 64-m telescope. Also, we report flux density measurements for aditional 76 Galactic SNRs from PMN North survey, at the same frequency. These observations are from Green Bank 43-m (23 SNRs) and 91-m radio telescopes (53 SNRs). In total, we estimate flux density of 197 Galactic SNRs at 4.85 GHz using PMN survey. Some 4% of all Galactic SNRs, we could not estimate fluxes due to blank fields (no bservations) or large size of the SNRs(>30 arcmin). Also, considerable number of SNRs (~10%) are embedded in surrounding HII regions or simply are not resolved (SNR sizes below 5 arcmin). We examine flux density distribution and surface brightness of whole Galactic SNR sample at 4.85 GHz (PMN). For shell type SNRs, power law index (beta) with value beta=-2.96+-0.34 was estimated. Using Sigma--D relation, we estimate distances for shell type SNRs and examine distribution of SNRs throughout our Galaxy.
Filipovic Miroslav , Graeme White , Thomas Pannuti , Quentin Parker
Individual radio pulses from pulsars have intensity-phase profiles that differ widely from pulse to pulse, from the average profile, and from phase to phase within a pulse. This variability does not have a widely accepted explanation and nor is there agreement over the radiation's emission mechanism. Here, by analysing data from the Vela pulsar, we show that the pulsar's variability has a well-defined functional form: lognormal field statistics. Stochastic growth theory (SGT) predicts lognormal statistics for a purely linear system close to marginal stability, while other theories predict different statistics. The simplest interpretations are that the Vela pulsar's variability is consistent with the emission mechanism being purely linear (either direct or indirect) and the source plasma being in an SGT state, with no evidence for nonlinear processes like wave collapse which produce power-law statistics. Viable nonlinear processes are strongly constrained: they must produce lognormal statistics when suitably ensemble-averaged. Similar results are found for normal pulses from two other pulsars, while giant pulses and giant micropulses show different statistics. Field statistics are thus a powerful, potentially widely applicable tool for understanding variability and constraining mechanisms and source characteristics of coherent astrophysical and space emissions.
Johnston Simon , Das Pritha
We present the observation results of PSR1937+21 at the Kashima 34m-antenna for five years. To redeem a not so large effective area of our antenna, we developed a highly sensitive observation system which includes the Acousto-Optic Spectrometer (AOS) with 200MHzBW in total (200kHz x 256ch x 4units). By using above system, we have been conducting the weekly observations of PSR1937+21 in S-band since November '97. From the data in the five years' span (Nov.'97 - Dec. '02) with 50MHz BW, we obtained the pulsar position in a good agreement with other reports, with daily-averaged timing residuals of 2.65 microsecond. TEMPO11.005 is used for the parameter fitting analysis. We also analyzed our data merged with the Parkes data in '95, and obtained the frequency stability sigmaz of 2x10^-14 at the time interval of 6.5 years. It rivals the best stability in the previous report. Results of timing PSR1937+21 at two frequencies (0.6 and 2.3 GHz) and analysis, made jointly with the Russian group in more than 5 years, will be presented at this symposium too. We appreciate M. Bailes in Swinburne University of Technology and the collaborators for allowing us to use the Parkes data.
Shibuya Yasuhisa , Nakagawa Fumimaru , Sekido Mamoru , Hosokawa Mizuhiko , Imae Michito
The radiation of high energetic gamma-ray photons not only gives rise to stochastic trajectories, but also generates instabilities due to density fluctuations and velocity fluctuations. These fluctuations will couple non-linear electrostatic oscillations to electromagnetic plasma waves via the magnetic field inhomogeneity that is inevitable in a pulsar environment. The model presented in this paper uses cylindrical geometry in which the axial magnetic field is radially non-uniform. The coupling mechanism uses the grad B drift to break the azimuthal symmetry in the velocity fields of the electrons and positrons in an electrostatic disturbance, producing an oscillating current source that drives an electromagnetic plasma wave away from the source. The ramifications of this effect for efficient co-rotating radiation mechanisms are explored.
da Costa António A
We have used HST/STIS to observe the young Crab pulsar and the middle-aged PSR B0656+14. The Crab pulsar was observed in both the near- and far-UV, and together with ground-based data we establish a spectrum that covers 1140-9250 A. A flat spectrum with a power-law index of 0.11+/-0.04 fits the entire spectral region. With the time-tag mode of the spectrograph we obtain the pulse profile, and show that the near- and far-UV profiles are similar, although the primary peak is marginally narrower. In the far-UV spectrum we also see evidence of blueshifted absorption in C IV 1550 A out to 2500 km/s, which could be a sign of the long-debated fast shell around the pulsar. PSR B0656+14 was observed using the prism mode of STIS/MAMA in the near-UV, and with this observation we have made it the first middle-aged pulsar for which a UV pulse profile has been established. Preliminary analysis shows two distinct pulses per the pulsar period in near-UV, which is in contrast to a single pulse detected in radio and soft X-ray ranges.
Lundqvist Peter , Sollerman Jesper , Shibanov Yura , Lindler Don , Koptsevich Alexi
Four double neutron-star (DNS) pulsars are currently known in the Galaxy. We have studied the formation of such systems from Be/X-ray binary progenitors, by investigating two crucial phases in the evolutionary path that connects the two types of system: (1) the common-envelope (CE) phase that ensues when the Be star expands and fills its Roche lobe, leading to a short period helium-star neutron-star binary; (2) the subsequent mass transfer from the helium star to the neutron star. We present detailed evolutionary calculations of the latter phase, showing that such
a mass transfer phase from helium stars between about 3.3 and 6 solar masses can explain the properties of the close-orbit PSRs B1913+16 and B1534+12. On the other hand, mass transfer from lower-mass helium star can lead to a second CE phase and produce very short-period DNS systems, with very short merger timescales (< 1 Myr). These are very unlikely to be observed due to their short lifetimes, but they may dominate the merger rate of DNS. From our calculations we estimate the galactic DNS merger rate to be between 0.4 and 6 per million years.
We present a detailed analysis of spectral data from the Chandra observation of 1WGA J1713.4-3949, a compact source located at the center of SNR G347.3-0.5. The object properties are similar to those of other Compact Central Objects (CCOs), which are found at the centers of SNRs, but show no evidence for either radio or X-ray pulsations. The best spectral fit for 1WGA J1713.4-3949 is obtained for a blackbody spectrum with temperature ~0.4 keV combined with a power law component with photon index of ~4.1. Such a two-component model is also similar to what is seen in Anomalous X-ray Pulsars (AXPs) and consequently we conducted a timing analysis using our time-exposure Chandra data for periods longer than 6.4 s. We find no significant evidence for pulsations in the current data. More sensitive timing observations are currently being pursued.
This work was supported in part from Chandra grant G00-1123X.
Slane Patrick , Gaensler Bryan , Plucinsky Paul , Hughes John P, Galloway Duncan , Crawford Fronefiel
The interaction of supernova remnants (SNRs) with dense molecular clouds impacts greatly on both kind of objects. Shocks driven by an SNR into a molecular cloud will compress, accelerate and heat the gas, and can contribute to disruption of the molecular cloud and trigger formation of new stars. We present observations of millimetre and near-infrared emission from shock waves driven into molecular clouds by adjacent supernova remnants. A sample of objects (G349.7+0.2, G359.1-0.5, Tornado, CTB 33, W28) is used to examine the signatures and consequences of SNR expansion into molecular clouds.
Wardle Mark , Green Anne , Whiteoak John , Burton Michael , Yusef-Zadeh Farhad
In the radio band, SNRs and pulsars are best identified by observing at low frequencies, where their steep spectra make them easily distinguishable from thermal sources. Motivated by these considerations, we have carried out a deep 330-MHz observation of the Andromeda Galaxy, M31, using the Very Large Array. In a single four-hour pointing, we were able to achive a (one-sigma) sensitivity of 0.6 mJy at 6-arcsec resolution over a two degree field of view. From our analysis of these data we identify 405 distinct radio sources in M31. While most of these sources are unresolved background radio galaxies, we find several steep spectrum sources, some radio counterparts of optical SNR candidates, and some radio jets from AGNs. We have also identified several complex sources which are as yet unidentified.
Lazio Joseph
Over the past 5 years, RXTE has detected four accreting millisecond X-ray pulsars. These have provided direct evidence that the millisecond radio pulsars are low-B (~10^8 G) neutron stars spun up via accretion from a companion star. In this scenario, radio pulses are expected to emerge after the accretion (and the x-ray emission) fade.
We have observed three of these sources with the Very Large Array, both during and after X-ray outburst. Surprisingly, we have detected at least two, but only during the X-ray outburst, suggesting a tight link between the accretion and the radio synchrotron radiation. The radio properties are similar to the incoherent synchrotron emission from microquasar transients rather than pulsars: the emission is associated with the X-ray state transition, is non-pulsed, has a flat(ish) spectrum, and, assuming Tb < 10^12K, is from a region of large size > 3.10^6 km, indicating a non-magnetospheric origin. Which is surprising since there is a tight correlation between the X-ray and radio decays. On the other hand, radio searches have found no pulsed radio emission during and after the X-ray outburst, in keeping with non- detections reported by others for pulsed radio emission from X-ray pulsars in quiescence.
Rupen Michael P, Dhawan Vivek
PSR J2021+3651 was discovered with Arecibo during a search for pulsations in the direction of the X-ray source AX J2021.1+3651, which is coincident with the high energy EGRET gamma-ray source GeV J2020+3658. GeV J2020+3658, also known as 2CG 075+00 and 3EG J2021+3716, is the 10th brightest Galactic source above 1 GeV. The hard spectrum and low variability of this gamma-ray source make it similar to the known gamma-ray pulsars. PSR J2021+3651 is young (tau_c = 17 kyr) and energetic (dE/dt = 10^36.5 erg/s), with a spin period of 104 ms and a high dispersion measure (DM = 369 pc/cm^3), which implies a distance > 10 kpc as well as high X-ray and gamma-ray efficiencies. Timing observations of this pulsar are ongoing and the pulsar has already been observed to glitch. We have recently obtained a 20 ks Chandra ACIS observation of PSR J2021+3651, which shows a point source surounded by what is likely a pulsar wind nebula with an extent of ~20''. A 20 ks Chandra observation taken in continuous clocking mode was also obtained. Here we present the results of timing observations with Arecibo, our Chandra observations, and also combined VLA observations in A, C, and D arrays.
Roberts Mallory S, Ransom Scott M, Kaspi Vicky M, Tam Cindy , Freire Paulo C
We test the physical model of the jets in SS 433 that was proposed by Marshall, Canizares and Schulz using additional observations with the Chandra High Energy Transmission Grating Spectrometer. The new observations sampled different precessional and orbital phases, offering different views of the jets through local material. Preliminary results indicate that the jet thermal structure has not changed drastically. The emission lines are broader than expected in one observation, so the jet opening angle has increased by a factor of two. In two observing periods, the low energy lines were substantially weaker, probably due to obscuration. These two observations were obtained at precession phases where the jets
Lopez Laura , Kane Julie F, Canizares Claude R, Schulz Norbert S
Globular clusters are known to harbour a disproportionately large number of millisecond pulsars (and other exotic pulsar systems) compared to the Galactic disk. Our team is conducting deep searches for radio pulsations at L-band (~20 cm) towards more than 30 globular clusters using the 305 m Arecibo telescope in Puerto Rico and the 100m Green Bank telescope in West Virginia.
The high time and frequency resolution of this data, along with newly developed search algorithms we are using, increase our sensitivity to sub-millisecond pulsations as well as pulsars in ultra-compact binary systems. With roughly half of our search data analyzed, we have discovered a total of nine new millisecond pulsars, eight of which appear to be in binary systems, and at least three which show eclipses. We have recently determined timing solutions (i.e. accurate positions, orbital ephemerides, and pulsar spin-down rates) for several of these systems and discuss their implications. We would like to acknowledge funding of this work by the Canadian Foundation for Innovation, NSERC, and a McGill University Tomlinson Fellowship.
Ransom Scott M, Stairs Ingrid H, Kaspi Vicky M, Freire Paulo C, Backer Donald C, Lorimer Duncan R
The young pulsar PSR J1740-3052, discovered in the Parkes Multibeam Pulsar Survey, is in a highly eccentric 8-month orbit with a companion of at least 11 solar masses. We present an up-to-date timing solution for this pulsar, incorporating effects likely due to the spin mass quadrupole of the companion star, and discuss what these data imply about the geometry of the orbit. We also discuss the interaction of the pulsar signal with the companion wind, observable as increased dispersive delays as the pulsar passes behind its companion. Finally, we present preliminary results from near-infrared spectroscopic observations of a coincident late-type star, aimed at determining whether or not this star is in fact the companion to the pulsar.
Manchester Richard N, Lyne Andrew G, Kramer Michael , Kaspi Victoria M, Camilo Fernando , D'Amico Nichi , Wagner Stefan
A VLA survey of the nearby galaxies: M83, NGC 4449, and NGC 6946 has identified over 40 candidate supernova remnants (SNRs). The majority of the candidate radio SNRs are associated with massive star forming regions and thus the SNRs are primarily remnants of massive star collapse supernovae, many of which should have produced neutron stars. Identification of pulsars in these nearby galaxies using current methods and instrumentation is not possible at this time. However, the SNRs can be used as probes of the local environments of the newly-made neutron stars. The global environments of the two grand design spiral galaxies, M83 and NGC 6946, will be compared to the global environment of the irregular galaxy, NGC 4449. Differences in the luminosity functions of the SNRs will be presented. Properties of the local environments (densities, magnetic field strengths, radial location within each galaxy, etc.) will be compared and discussed for each galaxy. Supernova rates have been estimated for each galaxy and the lower limits on massive star formation in each galaxy will be presented, these rates are crucial for estimating the neutron star population.
Dodson, McCulloch & Lewis (2002) exposed a unique short decay term associated with the Vela pulsar glitch of 2000. It suggested a nonsense crustal moment of inertia, 17 times the interior of the neutron star. Reevaluating this decay with higher resolution data, the highest of any glitch, shows a short-term decay that represents a core contribution to the near-instantaneous spin-up of the Vela pulsar.
Link Bennett , Dodson Richard
HETE-2 (High Energy Transient Explorer 2) monitors the sky region centered on the anti-sun direction in a wide energy band with two instruments: the Wide-Field X-ray Monitor (WXM: 2--25 keV) and the French Gamma Telescope FREGATE: 6--400 keV).
SGR1806-20 and SGR1900+14 were monitored with these intruments for about 60 days between June and August 2001 while they were within the field of view.
We have firmly detected 2 and 4 bursts from SGR1806-20 and SGR1900+14, respectively with both WXM and FREGATE. A burst from SGR1900+14 occurred at 2001 July 2, 03:34 UT had a high fluence of 8E-6 ergs/cm2 (6-40 keV) and a broad-band burst spectrum was obtained by WXM and FREGATE (GCN Circular 1078). The spectrum of this burst cannot be represented by single-component power-law or thermal bremsstrahlung spectra. We find that it can be well described by a model consisting of two blackbody components with different temperatures.
In this paper we discuss the results from HETE-2 on the bursts from the soft gamma-ray repeaters.
Torii Ken'ichi , Yoshida Atsumasa , Shirasaki Yuji , Tamagawa Toru , Sakamoto Takanori , Atteia Jean-Luc , Barraud Celine , Fenimore Edward E, Ricker George
In a birefringent medium, electromagnetic radiation propagates in two natural modes with orthogonal polarization. Differing dispersion of these modes induces a phase delay that may be viewed as a rotation of the polarization vector about an axis defined by the natural modes, which are antiparallel in this space. In a cold, magnetized plasma, the natural circular modes cause Faraday Rotation of the linearly polarized component by an amount that varies with frequency, f. Formation of the complex quantity, P(f)=Q(f)+iU(f), enables the use of the Fourier Transform in the study of this effect. However, in a relativistic plasma, the natural modes may be elliptically polarized, and a formal description of Generalized Faraday Rotation requires a three-dimensional treatment. We discuss the hyper-complex quantity, H(f)=I(f)+iQ(f)+jU(f)+kV(f), and its Quaternion Fourier Transform; and consider its application in the polarimetric study of pulsar emission.
Edwards Russell
We describe progress in simulating the formation of the pulsar magnetosphere and its wind. Using relativistic particle-in-cell simulations, we show that for space-charge limited emission of charges from the surface of the neutron star the magnetosphere is not filled with plasma, but forms a nonneutral dome-torus "electrosphere". This configuration persists even for oblique rotators. We show that the electrosphere is unstable to diocotron instability and present simulations of nonlinear development of the instability for arbitrary magnetic inclination angles. Diocotron instability is found to efficiently transport charge in the closed zone of the magnetosphere, filling it to Goldreich-Julian density. We also present results of time-dependendent modeling of magnetosphere formation using a new relativistic force-free MHD code for aligned split-monopole and dipole magnetic geometries.
Arons Jonathan
The Crab pulsar is one of the youngest pulsars known. It can be observed through a very wide frequency range, from low frequency radio all the way up to gamma-rays. Recently, Moffett and Hankins (1999) reported on high radio frequency observations in full polarization, which demonstrated the presence of additional to the main pulse components with high levels of linear polarization. They argue that the profile morphology and polarization properties indicate emission originating both near the star's surface and in the outer magnetosphere. We have conducted high quality polarimetric observations with the Effelsberg radio-telescope of the Crab pulsar at 8.35 GHz using a new, sensitive receiver with a very large bandwidth. We present our observations and discuss them in the context of the conclusions reached by the aforementioned authors.
Jessner Axel , Kundt Wolfgang
Pulsars are the objects in the universe with the strongest polarized emission, obviously due to their ultrastrong magnetic fields with which the emission is generated. Other classes of radio objects have in general much weaker polarization. The NRAO VLA Sky Survey have catalogued 2 million radio sources with linear polarization measurements. We have selected more than 300 radio sources, with a polarization percentage greater than 25%, as possible targets for pulsar searches. We believe that such a sample is not biased by the selection effect against the ultra-short spin periods or orbit periods. Using the Parkes 64m telescope and Jodrell Bank 76m telescope, we conducted searches with sampling interval 0.08ms and so we were sensitive to submillisecond pulsars. Unfortunately we did not find any new pulsars. This implies that either radio pulsars do not have pulse periods of less than 1ms, or submillisecond pulsars are not highly polarized radio sources.
Manchester Richard N, Lyne Andrew G, Qiao Guojun
A new model for polarization of pulsar radio emission is discussed. In this model, the radio emission is assumed to be produced in either two orthogonal modes or their superposition, propagating through pulsar magnetospheric plasmas. The plasmas are assumed to be relativistic and asymmetric with nonzero imbalance between electron and positron number densities so that all relevant wave modes are elliptically polarized. The Stokes parameters are evaluated in terms of the polarization ellipticities. The observed mode switch can be due to either presence of the two modes or a 90 degree rotation of an ellipse through propagation. In the former case, orthogonal mode jump is predicted to relate to a sign flip in circular polarization (CP). In the latter case, a mode change should correspond to a maximum in CP. These predicted features are tested against the observations. Since the polarization ellipses depend on the pair mulitplicity (number of pairs produced per primary particle), which is determined explicitly by the pulsar parameters, the observed polarization features should generally vary with the pulsar period and magnetic field.
Melrose D.B.
Both polar gap and outer gap may exist in young pulsars, producing observable electromagnetic radiation. In this talk, I will discuss the constraint on the formation of a polar gap by acceleration in the outer gap. Particle acceleration and subsequent electron-positron cascade in the outer gap (located near the null surface) generate a return flux of electrons (or positrons) to the polar gap, reducing pair production in the inner magnetosphere. It is suggested that in young pulsars, strong acceleration leads to an inefficient pair production near the polar cap. I will discuss particularly the possibility that acceleration in the polar gap is quenched due to the return flux and that the observed radio from young pulsars originates from the outer magnetospheric regions where efficient pair cascades can occur.
Nasu is a 1000 years historical place 160km north of Tokyo. In Nasu Pulsar Observatory of Waseda University, eight spherical dishes of 20m in diameters were built in Feb 2003, and a 30m spherical dish is constructing as a first dish of an another eight element array. HEMT receivers are used at 1.4 GHz in normal temperature and the receiver noise temperatures are less than 40K. Band width is 20MHz and base band I/Q outputs are used as analytic signals for spatial-temporal complex Fourier transform in eight beam observation.
A present eight element interferometer is a survey facility searching pulsars and transient radio sources using the spatial-temporal FFT processor. Observed declinations are limited between +32 deg to + 42 deg because asymmetrical Gregorian sub reflectors are used and they rotate only around Az axis. In 30m spherical dish, 2D tracking sub reflector(observed declinations are from +55 deg to +19 deg) is designed for pulsar timing observations as well as a base band recording disk array. As a phase 1 observation we are searching transient radio sources and pulsars associated with EGRET Gamma-ray objects.
Asuma Kuniyuki , Takeuchi Hiroshi , Kuniyoshi Masaya , Matsumura Nobuo , Ichikawa Hajime , Okubo Riki , Sawano Sawano , Takefuji Kazuhiro , Yoshimura Naoya
Comparing the XMM-Newton Galactic Centre Survey with corresponding Chandra observations taken several months later, we have found evidence for a new population of transient X-ray sources which have peak X-ray luminosities of only Lx~10^34 erg/s. Their X-ray spectra are interesting - in one such source, XMM 174544.4-291259, we find a strong helium-like iron line with an equivalent width of ~2 keV. This source population may contribute significantly to the hard, apparently diffuse, emission seen in the Galactic Centre Region which has previously been interpreted in terms of a wide spread distribution of very hot thermal plasma. Here we summarise our results relating to these transient sources and consider the possible nature of the population.
Warwick Robert S, Decourchelle Anne , Wang Q. D
Pulse-shape changes have been observed in Vela in the radio regime and have been shown to correlate with flux (Krishnamohan \& Downs 1983). We aimed to look for similar correlations in the x-ray regime. However, unlike the radio time series, the list of x-ray photon arrival times affords us no ability to compare a single x-ray pulse shape with its corresponding flux. Instead, we use simultaneously acquired radio data from the Mount Pleasant Radio Observatory in Tasmania to sort the x-ray photons into groups according to the flux of the corresponding radio pulse. In this way we construct several different integrated x-ray profiles corresponding to different radio-pulse strengths. We present the results of the comparison.
Lommen Andrea , Harding Alice , Strickman Mark , Gwinn Carl , Dodson Richard, Moffet David , McCulloch Peter
Turbulence, or turbulent-like structures, in the interstellar medium when combined with motions of the medium and the pulsar-earth line of sight lead to observable changes in pulse arrival time via dispersion measure changes and multipath propagation or pulse broadening. Multi-frequency precision timing of the millisecond pulsar B1937+21 allow us to detect many of these observables in one object. We discuss an archive analysis project to assemble a multi-decade record of the dispersion, scattering, and refractive scintillation record of B1937+21 at frequencies between 327 MHz and 2400 GHz using the 85ft and 140ft telescopes in Green Bank, Arecibo, and Nancay. One particular feature of this record is the demonstration that "the" dispersion measure is not unique, but rather is frequency dependent owing to scattering: the low frequency dispersion is averaged over a larger volume of the intervening plasma than at high frequencies. This effect can be scaled to other pulsars and other frequencies to assess its affect on "precision pulsar clock" experiments. A further goal for this report is to assemble what is known about dispersion measure temporal variations in all carefully studied pulsars, and to explore how the variations scale with dispersion measure.
Ramachandran R.
A long transient outburst of the Be/X-ray binary KS 1947+30 took place between 2000 November and 2001 June. Frequent observations with the Rossi X-ray Timing Explorer satellite revealed significant orbital modulation of the 18.7 s pulsation as well as spin-up due to accretion torques. Pulse timing studies also provide evidence for an extremely rapid increase in the pulse frequency occurring on 2001 February 16.5, around 5 days after the peak of the outburst. At this time the spin-up torque was close to the maximum reached during the outburst, at approximately 2e-11 Hz/s. Over a time interval of at most a few hours the pulse frequency increased by 1.8e-6 Hz, corresponding to a fractional change delta nu/nu of approximately 3.5e-5. The frequency increase was not accompanied by an unusual rise in the X-ray flux, as might be expected for an episodic accretion event. One possible explanation for the increase is a stepwise change in frequency, analogous to the ``glitches'' typically observed in young radio pulsars and anomalous X-ray pulsars. If this interpretation is correct, then an entirely new sample of pulsars may be available for studies of glitches as probes of neutron star structure.
Morgan Edward H, Levine Alan M, Chakrabarty Deepto
The Parkes multibeam survey and its discovery of over 600 pulsars, has opened up new avenues for probing the Galaxy's electron content and magnetic field. We present results from recent Arecibo observations of a large sample of high-DM pulsars (of which 41 are from the multibeam survey) at multiple frequency bands from 0.4 to 2.4 GHz. The data are used for multiple science goals. We employ a CLEAN-based deconvolution method that enables measurement of the pulse-broadening time and determination of the pulse-broadening function (PBF), as well as reconstruction of the intrinsic pulse shape. The new measurements are compared with predictions from the Galactic electron density model. The data show evidence for excess scattering toward many lines of sight, which we interpret in terms of "clumps" of enhanced scattering. Further, we examine the scaling of pulse-broadening time with frequency, and discuss the implications for wave-number spectrum of density irregularities. While departures from the traditional $\sim \lambda ^{4.4}$ behavior is seen in several cases, our analysis also suggests that the inferred scaling index depends on the type of the PBF adopted. We also present new measurements of rotation measures, and discuss the implications for the magnetic field structure of the Galaxy.
Cordes Jim , Camilo Fernando , Nice David , Lorimer Dunc , Chatterjee Shami
The challenge in searching for non-radio-pulsing isolated neutron stars (INSs) is in excluding association with objects in the very large error boxes (~13", 1 sigma radius) typical of sources from the largest X-ray all-sky survey, the ROSAT All-Sky-Survey/ Bright Source Catalog (RASS/BSC). We search for candidate INSs using statistical analysis of optical (USNO-A2), infrared (IRAS), and radio (NVSS) sources near the ROSAT X-ray localization, and show that this selection would find 20% of the INSs in the RASS/BSC. This selection finds 32 candidates at dec.>-39 deg, among which are two previously known INSs, seventeen sources which we show are not INSs, and thirteen the classification of which are as yet undetermined. These results require a limit of <67 INSs (90% confidence, full sky, assuming isotropy) in the RASS/BSC. This limit modestly constrains a naive and optimistic model for cooling NSs in the galaxy.
Fox Derek W, Bogosavljevic Milan , Mahabal Ashish
We present characteristics of pulsar high-energy radiation as predicted by the recently proposed caustic model (Dyks and Rudak 2003). Variations of polarization degree and position angle as a function of rotation phase are confronted with the optical data on the Crab pulsar and compared to predictions of polar cap and outer gap model. We find prominent differences between the polarization properties predicted by the models. We show that relative positions of features observed in gamma-ray and radio lightcurves find a natural interpretation within the caustic model.
Harding Alice K, Rudak Bronislaw
LS I +61 303 is a remarkable X-ray and gamma-ray emitting Be + neutron star binary, with periodic (26.5day) radio outbursts. A recent Bayesian analysis demonstrates that the orbital phase and peak flux density of the outbursts exhibit a 4.6 year periodic modulation. We present a model that accounts for the radio properties in terms of variable accretion by the neutron star in an eccentric orbit, embedded within the dense equatorial wind of the rapidly rotating Be star. The neutron star thus acts as a probe of the wind speed and density. The analysis indicates that the 4.6 year periodic modulation in radio properties results from an outward moving density enhancement or shell in the Be star equatorial disk. We propose that each new Be star wind enhancement cycle may be triggered by the interaction of a short lived relativistic wind (ejector phase) from the neutron star, with the Be star. Our best estimate of the mass accretion rate of the neutron star is in the range 0.001 to 0.01 of the Eddington accretion limit. This translates to an expected luminosity range of 10^35 to 10^36 ergs/s, which is comparable to the total X-ray and gamma-ray luminosity.
Neish Catherine D
In a binary stellar system, characterized by violent phases, a few combination of recoil velocities and masses can leave two neutron stars, of compatible mass, bound in an eccentric orbit, as found amongst high mass binary pulsers (HMBPs). An important problem in quantum and classical stasistics is the parametrization of the ground state. In this context the variational principle is adopted from the semi-classical approach, to formulate a criterion which tends towards energy minimization and enables gravity softening, to study the orbital trends in binary neutron stars on the basis of statistical mechanics. results indicate that high eccentricities are favored initially; but the orbit circularizes in a large timescale. This indicates a scenario in which, after the initial violent phase leading to their formation and after attaining a quiescent phase, HMBPs are expected to aquire high eccentricities and circularize their orbits slowly. Notice that the HMBP 2303+46 has highly eccentric orbit with e = 0.7, while the relatively older one 1534+12 has a less eccentric orbit with e = 0.3. I would like to thank all those with whom I had helpful discussions (espacially Prof. V.B. Magalinsky).
We present preliminary results of 2D relativistic magnetohydrodynamical simulations of pulsar wind nebulae.
A growing number of plerions is found to show in the X-rays spatial features such as rings and jets. The latter are especially intriguing and their interpretation poses some theoretical difficulties. These jets, in fact, seem to originate from the very close vicinities of the central neutron star, at a much shorter distance than that at which the shock in the equatorial part of the flow is observed to be. Due to the theoretical difficulties at explaining self-collimation of a highly relativistic flow, it has been recently suggested that collimation is actually taking place behind the pulsar wind termination shock, where the flow is only mildly or non-relativistic. We investigate, within the framework of relativistic MHD, the possibility that some latitude dependence of the wind energy causes the termination shock to be much closer to the pulsar along the rotation axis than in the equatorial plane. We study the geometry of the shock and the spatial structure of the downstream flow as a function of the latitude dependence of the wind at injection.
Del Zanna Luca , Bucciantini Niccolo'
In this paper we report on calculations of the pulsar birthrate based on the results of the Parkes multibeam survey. Based on the observed sample of more than 800 pulsars, we compute the `pulsar current', accounting as accurately as possible for all known selection effects. The main goal of this paper is to understand the differences between birthrates of pulsars in different ranges of surface dipole magnetic field. We show that pulsars with magnetic fields greater than 10 to 12.5 G account for about half of the total birthrate.
Manchester Richard N, Hobbs George B, Lyne Andrew G, Kramer Michael , Camilo Fernando , Stairs Ingrid H, Kaspi Victoria M, D'Amico Nicolo , Possenti Andrea
The Vela pulsar should be everyones favourite object. It is the brightest pulsar in Radio, it was the object that told us (via its glitching) that pulsars were solid rotating bodies not oscillating ones. It provides a major basis for estimates of pulsar interiors, distances, luminosities, and SNR characteristics. Therefore it is of vital importance we know where it is going, what is happening around it and what is happening within it.
By coincidence we have recently produced results in all of these areas for this key pulsar.
Legge David , Reynolds John , McConnell David , Lewis Dion , Deshpande Avinash A
Using Gaussian fit separation of the average profile (GFSAP) method, we re-examined the average profiles of ten pulsars at several frequencies, ranging from 408MHz to 1642MHz. This method allows us to study the pulsar emitting geometry carefully. The fitting results reconstruct the original profile very well within the statistical limitation of the errors in the observation. The 11 pulsars are the PSRs B0402+61, B0450-18, B0740-28, B1039-19, B1237+25, B1737+13, B1804-08, B1831-04, B1857-26, B2111+46 and B2310+42.
From the fitting procedure, we can get the component-number for each pulsar, and the parameters for every component. Among them there are four pulsars with classifications different with Rankin?s of 1993. The PSRs B0740-28 and B2111+46 are the five components rather than triple, PSR B1039-19 and B2310+42 are the four components.
The energy of each component for the 11 pulsars were calculated. The spectral difference between core and conal components is very apparent. The spectra indices of the core component are lager than the conal ones for every pulsar. And the inner cone indices also seem to be larger than those of the outer cone.
keywords Pulsar, average profiles, fitting, spectrum
Wu Xinji
The individual pulses and integrated profile of PSR 0826-34 have been seriously studied using Parkes observation data at 1.4GHz. The investigation revealed some unseen integrated profile and subpulse drifting behaviors of PSR 0826-34. A brand new view should be taken to this Pulsar.
Kramer Micheal , Lyne Andrew G, Manchester R N, Wu Xinji
The individual pulses and integrated profile of PSR 0826-34 have been seriously studied using Parkes observation data at 1.4GHz. The investigation revealed some unseen integrated profile and subpulse drifting behaviors of PSR 0826-34. A brand new view should be taken to this Pulsar.
Kramer Micheal , Lyne Andrew G, Manchester R N, Wu Xinji
We present a relativistic model of pulsar radio emission by plasma accelerated along the rotating magnetic field lines projected on to a 2D plane perpendicular to the rotation axis. We have derived the expression for the trajectory of a particle, and estimated the spectrum of radio emission by the plasma bunches. We used the parameters given in the paper by Peyman and Gangadhara (2002). Further the analytical expressions for the Stokes parameters are obtained, and compared their values with the observed profiles. The one sense of circular polarization, observed in many pulsars, can be explained in the light of our model.
In this paper we present results on the ongoing development program of High Energy Replicated Optics (HERO) and fine pixel Cadmium Zinc Telluride (CZT) detectors to match the spatial resolution of HERO (15 arc-sec in the energy range 1-70 keV). Initially the payload is planned to be flown on a ballon borne platform with an expected sensitivity of few milli-Crabs in a 3 hour observation and down to 100s of micro-Crabs on ultra long duration flights.
Ramsey Brian D, Speegle Chet , Engelhaupt Darell , Apple Jeff , Gaskin Jessica A, Finger Mark H
Analysis and modeling of the unusual system LSI+61 303 is presented. The multi-wavelength spectrum of LSI+61 303 is summarized and described in terms of a physical emission model. The system is modeled as a pulsar wind nebula expanding inside the environment provided by the Be companion's stellar wind and photon flux. A set of equations describing the system is developed and solved numerically for representative sets of parameters. X-rays through gamma-rays are due to inverse Compton emission from relativistic electrons around the pulsar. The radio emission is due to synchrotron emission of varying optical depth, which yields a varying spectral index. The peak of x-ray emission is near periastron and the peak of the radio emission is near apastron, due to reduced confining pressure on the relativistic electron cloud and its subsequent rapid expansion.
This work supported by the Natural Sciences and Engineering Research Council of Canada.
The featureless spectra of isolated "neutron stars" may indicate that they are actually bare strange stars, but a definitive conclusion on the nature of the compact objects cannot be reached until accurate and theoretically calculated spectra of the bare quark surface are known. However, due to the complex nonlinearity of quantum chromodynamics, it is almost impossible to present a definitive and accurate calculation of the density-dominated quark-gluon plasma from the first principles. Nevertheless, it was suggested that cold quark matter with extremely high baryon density could be in a solid state. Within the realms of this possibility, we have fitted the 500ks Chandra LETG/HRC data for the brightest isolated neutron star RX J1856.5-3754 with a phenomenological spectral model, and found that electric conductivity of quark matter on the stellar surface is about $1.5\times 10^{16}$ s$^{-1}$.
Zhang Xiaoling , Zhang Shuangnan
A model is developed here to reproduce the pulse shape of Her X-1. The 35-day cycle of pulse shape changes during the 35-day Her X-1 cycle "High -- Low -- Short High -- Low" is caused by varying obscuration of the emission region by the accretion disk (Scott, Leahy, Wilson 2000,ApJ, 539, 392). The observed sequence of pulse shape changes imply a pencil beam from the near pole and a fan beam from the far pole. Using a newly developed code for modeling accretion column emission, including accurate treatment of gravitational light- bending effects, the observed pulse shape of Her X-1 is modeled here. The resulting constraints on the size and shape of the accretion column and on the radius of the neutron star are given.
This work supported by the Natural Sciences and Engineering Research Council of Canada.
We highlight the timing and emission properties of pulsars recently discovered in Arecibo drift-scan searches. Among these pulsars are two millisecond pulsars, J1453+09 and J1944+09, and the 56-ms pulsar J0610+21. We discuss the unique pulse profile morphology and drifting subpulse behavior exhibited by the 645-ms pulsar J0815+09 and present polarization measurements.
Lorimer Duncan R, Arzoumanian Zaven , Backer Donald C, Cordes James M, Fruchter Andy S, Lommen Andrea N, Xilouris Kiriaki
The Tycho SNR, as one of the few historical SNRs, has been widely studied in various wavebands. There are obseravtional evidences suggesting that the Tycho SNR is expanding in a medium with density gradient and possibly interacting with dense ambient medium toward the northeast direction. From the FCRAO 12CO survey of the outer Galaxy, we have identified a patch of molecular clouds which could be associated with the Tycho SNR and have conducted a follow-up observation with Nobeyama 45m telescope.
We present the Nobeyama 12CO data which has higher spatial and specral resolution. The mophology of the molecular cloud suggests that the dense medium interacting with the SNR is possibly the molecular cloud. Distance estimate to the SNR and molecular cloud indicates that they are at the same distance. We also discuss a possible connection between molecular cloud and optical knots observed.
Koo Bon-Chul , Tatematsu Ken'ichi
Structure of cold and hot dense matter at subnuclear densities is investigated by quantum molecular dynamics (QMD) simulations. We succeeded in showing that the phases with slab-like and rod-like nuclei etc. can be formed dynamically from hot uniform nuclear matter without any ssumptions on nuclear shape. We also observe intermediate phases, which has complicated nuclear shapes.Geometrical structures of matter are analyzed with Minkowski functionals, and it is found out that intermediate phases can be characterized as ones with negative Euler characteristic. Our result suggests the existence of these kinds of phases in addition to the simple ``pasta'' phases in neutron star crusts.
Watanabe Gentaro , Yasuoka Kenji , Ebisuzaki Toshikazu
PSRs J1718-37184 and J1847-0130 are radio pulsars with 3.4 and 6.7 second spin periods discovered in the Parkes multibeam survey of the Galactic plane. The slowdown rates for these pulsars are high and imply surface dipole magnetic field strengths of nearly 10^14 G. These inferred dipolar magnetic field strengths are the highest by far among all known radio pulsars and over twice the ``quantum critical field'' above which some models predict radio emission should not occur. The inferred dipolar magnetic field strength and period of these pulsars are in the same range as those of the anomalous X-ray pulsars, which have been identified as being ``magnetars" whose luminous X-ray emission is powered by their large magnetic fields. The properties of these pulsars prove that inferred dipolar magnetic field strength and period cannot alone be responsible for the apparent radio silence and unusual high-energy properties of the magnetars and creates new challenges for understanding the possible relationship between these two manifestations of apparently young neutron stars.
Stairs Ingrid H, Kaspi Victoria M, Lorimer Duncan R, Lyne Andrew G, Kramer Michael , Manchester Richard N, Camilo Fernando , Hobbs George , Possenti Andrea
During a project initiated in 1991, the expansion of the historical remnant of SN 1006 was determined at radio wavelengths through a direct comparison of images made of the remnant in 1984 and 1991 using the Very Large Array. The success of this project spurred the expansion study of another historical remnant: Tycho's supernova of 1572. The bright Tycho SNR revealed amazing results, showing non-uniform expansion along its eastern rim, which was later found to correspond with expansion into a region of high density HI-emitting gas. Both remnants were found to be in a pre-Sedov phase of SNR evolution.
Now, nearly twenty years after the first-epoch observations were made of each remnant, a set of third-epoch VLA observations have been completed to measure the radio expansion of both remnants with higher precision. In addition, we have improved the signal-to-noise of our latest SN 1006 image through use of the Australia Telescope Compact Array, thus improving our expansion measurement.
We present results showing the dynamics of the two historical remnants over the past 20 years, and compare our work with recent studies at optical and X-ray wavelengths.
Reynoso Estela , Hughes John
We present an updated phase-coherent timing solution for the young, energetic pulsar PSR B1509-58 for twenty years of data. We have measured a stable braking index of n=2.841+/-0.001, in agreement with the value reported in 1994 by Kaspi et al. There is clear evidence for "red" timing noise in the residuals of the pulsar in addition to a sizable third derivative. A partially phase-coherent timing study was done in order to minimize contamination from timing noise; we report a measured value for the third frequency derivative of (8.5+/-0.5)E-32 s^(-4), in agreement with the previous value reported by Kaspi et al. This value implies a second braking index of 12.1+/-0.2, less than the predicted value of 13.3. Under the assumption that the measurement is not contaminated by timing noise, this result suggests that the magnetic field of the pulsar experienced growth in the past, as shown by Blandford (1994).
Livingstone Margaret A, Manchester Richard N
We searched HI 21 cm line emission from shocked atomic gas associated with southern supernova remnants (SNRs) using the Southern Galactic Plane Survey. Among 97 sources, we detected 10 SNRs that have associated high-velocity HI gas, most of which are quite possibly the gas accelerated by the SN blast wave. We also detected 5 SNRs that possibly have associated HI shells. These 5 sources show an excess HI emission significantly brighter than the surrounding region over a wide (>10 km/s) velocity interval. We present the results on these 15 SNRs. For G347.3-0.5 (RX J1713.7-3946), we also present high-resolution (~2 arcmin) HI images and compare them with the X-ray morphology of the SNR.
Kang Ji-hyun , McClure-Griffiths Naomi