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20th of August 2020
Radio pulsations from the gamma-ray millisecond pulsar PSR J2039-5617
by Corongiu et al.
About two thirds of known milli-second pulsars (MSPs) are in binary systems, usually with white dwarf companions and with orbital periods of up to hundreds of days. Some binary MSPs, however, have non-degenerate low-mass companions and very short orbital periods, of less than a day. These are known as "Redbacks", and have companions with masses of 0.1 ~ 0.4 solar masses which are partially ablated by irradiation from the pulsar wind. (Redbacks are related to the "Black Widow" binary systems which have lighter companions, with masses less than 0.05 solar masses, that are almost fully ablated.) The Fermi gamma-ray source 4FGL J2039.5−5617 showed properties consistent with it being a redback pulsar, and this was recently confirmed by the discovery of gamma-ray millisecond pulsations with a period of 2.6 milliseconds. Corongiu et al. observed 4FGL J2039.5−5617 with the Parkes radio telescope in 2016 and 2019, and have recently confirmed the 2.6 ms period in the radio data. The 1.4 GHz data shows clear evidence of eclipses of the radio signal for about half of the orbit, a characteristic phenomenon in redback systems, which is associated with the presence of intra-binary gas. The image above shows a colour map of the radio pulse amplitude as a function of spin and orbital phase (vertial and horizontal axis, respectively). The occurrence of a signal eclipse over the orbital phase range 0.1 to 0.5 is apparent. The paper has been submitted to Monthly Notices of the Royal Astronomical Society.

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