Science from the ATCA

Below are some of the highlights of the science done with the Australia
Telescope Compact Array. The years given are those in which the observations
were published.


The ATCA is used to make the first image of a forming
radio supernova remnant (SNR 1987A).

Supernova 1987A was a star that exploded in a small neighbouring galaxy,
the Large Magellanic Cloud, which can be seen only from the Southern Hemisphere.
Light from the explosion reached us in 1987. SN1987A was the brightest
and closest supernova since the invention of the telescope four centuries
ago, and gave astronomers the best chance they’d ever had to gather
data on such explosions. The supernova put out an initial burst of radio
emission, then fell radio-quiet – until July 1991, when the University
of Sydney’s MOST telescope became the first radio telescope to spot
the re-emerging radio supernova remnant. The ATCA, working at higher frequencies,
detected this phoenix from the ashes about a month later, and was able
to make the first ever picture of such an emerging remnant.

An artist's impression of GRO J1655-40. The system
is believed to be a subgiant star orbiting a black hole 6-7 times the
mass of the Sun.
Credit: NASA

Astronomers using
the ATCA observe the longest radio jets ever found in a radio galaxy (galaxy

3D reconstruction of Jupiter's magnetic field from
20 cm ATCA data.
Image: G.Dulk, Y.Leblanc and R.Sault

The ATCA is used to make the first 3D images of
Jupiter’s radiation belts. These observations indicate the properties
of the magnetic field closer to the planet than spacecraft have been able
to measure.

Jupiter is a strong natural source of radio waves. Much of this radio
emission comes from its 'radiation belts' – regions of strong magnetic
field that ring the planet. The radio waves come from high-energy electrons
trapped in the belts. Because Jupiter rotates once every 10 hours, it’s
possible to see the planet from all sides. The 3D images are tomographic
reconstructions, built up from views taken at different angles as the
planet turns.

Image of the Large Magellanic Cloud made from combined
Parkes and ATCA data. Observers: S. Kim et al.

The ATCA is used
to make images of two neighbouring galaxies, the Large and Small Magellanic
Clouds, which are twenty times more detailed than any previous radio observations.

The Clouds are quite extended objects on the sky – to the eye the
Large Magellanic Cloud, for instance, covers about the same area as the
Moon. Over several years the telescope has literally pieced together the
most detailed pictures ever made of the neutral (atomic) hydrogen gas
in the galaxy – the ‘skeleton’ that underlies its visible
stars. The picture of the LMC was ‘mosaiced’ together from
1344 separate observations of the ATCA, and shows the galaxy to be shot
through with giant holes – ‘superbubbles’ – carved
out by exploding stars and stellar winds. It is the most detailed such
radio picture ever made of another galaxy.

Supernova 1998bw in the spiral galaxy ESO184-G82.
Credit: European Southern Observatory

observations are some of the first evidence that the explosions called
gamma-ray bursts are linked to exploding stars – supernovae.

The ATCA observed the region of the gamma-ray burst GRB 980425, detecting
a supernova, SN1998bw, in the galaxy ESO184-G82. The best evidence that
the two events were linked came from the estimate of the expansion speed
of the radio photosphere.

An optical image of 47 Tucanae (in blue) overlaid
with the point radio sources detected (in green).
Observers: D.McConnell,
R..Deacon, J.Ables

ATCA imaging of
the globular cluster 47 Tucanae–a ball of stars on the outskirts
of our Galaxy–reveals 11 point radio sources, 10 of which could
be identified as pulsars. The imaging technique provides a new way to
detect pulsars that is not subject to the selection effects of the most
common method of searching for pulsars: looking for periodic radio signals.


ATCA observations
of the giant radio galaxy B0114-476 suggest that the beams from its central
engine may have turned off, then restarted, after an initial phase of inactivity.
This may explain why giant radio galaxies become so large, with radio emission
more than 100 times the length of the optically detectable galaxy.


ATCA helps to provide candidate fields for the Hubble Deep Field South

– an apparently blank piece of sky for the Hubble Space Telescope
to observe. Like the previously observed Hubble Deep Field North, this
field proved to be rich in ancient galaxies.

observations with the ATCA detect an unusual object 5-11 billion light-years
distant, optically faint but radio-bright, which could be a new kind of

Supernova remnant SNR1987A, imaged by the ATCA at
18.5 GHz (12 mm wavelength) in August 2003.
Observers: R. Manchester et

ATCA makes the first image at short (12-millimetre) radio wavelengths
of the supernova remnant 1987A.

The cluster Abell 3667. The coloured image shows the
hot gas that lies in space between the galaxies. Yellow contour line show
the regions of radio emission, produced by shock waves in the gas as two
clusters collided. Radio data: 20 cm ATCA observations; X-ray data: ROSAT
(PSPC). Composite image by Melanie Johnston-Hollitt, University of Adelaide and ATNF, using the Synage++ Software of Matteo Murgia, Istituto di Radioastronomia, Bologna, Italy.

observations of Abell 3667, a cluster of about 500 galaxies, suggest that
it was produced by two smaller clusters merging.
This is the first
observational evidence for this process.


Data from the ATCA
and Parkes telescope are combined make the first measurement of the three-dimensional
structure of a face-on galaxy (the Large Magellanic Cloud).


ATCA and NASA’s Chandra X-ray space telescope capture the entire life-cycle
of jets from a microquasar
, XTE J1550-564, seeing for the first time
jets erupt at relativistic speeds, slow down and fade away.


ATCA helps show the association between the gamma-ray burster GRB 011121
and a supernova
, further clinching the connection between the two phenomena


ATCA observations of gamma-ray
burster GRB 030329 contribute to measuring the energy involved in the explosion.
The total energy release is similar to that of other gamma-ray bursters.
The observers conclude that gamma-ray bursters have a common origin–something
that was previously in doubt.


The ATCA detects an annual
cycle in the scintillating quasar PKS 1257-326. Astronomers
use this to develop a technique for high resolution imaging.
quasar, PKS 1257-326, is one of the three most rapidly varying known,
with its flux density showing changes of up to 40% in 45 minutes. How
fast and how strongly the flux varies depends on the size and shape of
the radio source, the size and structure of the gas clouds causing the
scintillation, the Earth's speed and direction as it travels around the
Sun, and the speed and direction in which the gas clouds are travelling.
The researchers have shown that by observing the variability of the radio
signal changes over the course of a year, one can create a very high-resolution,
two-dimensional picture of the radio-emitting regions of a quasar.

ATCA observations of scintillating quasars started in 1996, and were important
in overturning the belief that intra-day variability in quasars is intrinsic.


ATCA observes a neutron star with a jet travelling at relativistic speed
(a significant fraction of the speed of light) – the first time this
has been seen.
This observation challenges the idea that only black
holes can create the conditions needed to accelerate jets to such extreme