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Astronomers using ASKAP from CSIRO and MeerKAT radio telescopes from the South African Radio Astronomical Observatory have discovered and characterized ASKAP J173608.2-321635, a highly polarized, highly variable, steep spectrum radio source located just 4 degrees from the center of the Milky Way. They have largely ruled out most of the possible origins of this source, including stars, normal neutron stars, and x-ray binaries. According to the team, ASKAP J173608.2-321635 may belong to a new class of sources at steep spectrum.
Artist’s impression of the ASKAP J173608.2-321635 source. Image credit: Sebastian Zentilomo.
Many types of stars emit variable light across the electromagnetic spectrum.
With the enormous advances in radio astronomy, the study of variable or transient objects in radio waves is a vast field of study helping us to reveal the secrets of the Universe.
Pulsars, supernovae, flaming stars, and rapid radio bursts are all types of astronomical objects that vary in brightness.
“The strangest property of the ASKAP J173608.2-321635 signal is that it has very high polarization,” said Ziteng Wang, a doctoral student. studying at the Sydney Institute for Astronomy at the University of Sydney, CSIRO and the ARC Center of Excellence for the Discovery of Gravitational Waves (OzGrav).
“This means that its light oscillates in only one direction, but that direction rotates with time.”
“The brightness of the object also varies considerably, by a factor of 100, and the signal turns on and off seemingly randomly. We have never seen anything like it.
“At first we thought it could be a pulsar or some type of star that emits huge solar flares,” he added.
“But the signals from this new source don’t match what we expect from these types of celestial objects.”
ASKAP Gemini image J173608.2-321635. Yellow outlines show ASKAP detection, while cyan outlines show MeerKAT detection. The best suited positions of ASKAP and MeerKAT are indicated by yellow + and cyan x respectively. The inverted Y’s show the sources from the VVV catalog. The small pink outline is MeerKAT’s best astrometry constraint. Image credit: Wang et al., arXiv: 2109.00652.
ASKAP J173608.2-321635 was detected six times between January and September 2020 as part of the Australian Square Kilometer Array Pathfinder Variables and Slow Transients (ASKAP VAST) survey.
Astronomers then monitored the source with the MeerKAT telescope from November 2020 to February 2021 at a rate of 2 to 4 weeks.
“We surveyed the skies with ASKAP to find new unusual objects with a project known as Slow Variables and Transients (VAST), throughout 2020 and 2021,” said Professor Tara Murphy, astronomer at the Sydney Astronomical Institute at the University of Sydney and OzGrav.
“Looking towards the center of the Galaxy, we found ASKAP J173608.2-321635, named after its coordinates.”
“This object was unique in that it was initially invisible, became shiny, faded and then reappeared. This behavior was extraordinary.
After detecting six radio signals from the source over nine months in 2020, astronomers attempted to find the object in visual light. They found nothing.
They then turned to Parkes’ radio telescope and again failed to detect the source.
“The information we have has parallels with another emerging class of mysterious objects known as Galactic Center Radio Transients (GCRTs), including one dubbed the ‘cosmic burper’,” said astronomer Professor David Kaplan. at the University of Wisconsin-Milwaukee. .
“Although our new object, ASKAP J173608.2-321635, shares some properties with GCRTs, there are also differences. And we don’t really understand those sources, anyway, so that adds to the mystery. “
The team’s article will be published in the Astrophysics Journal.
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Ziteng Wang et al. 2021. Discovery of ASKAP J173608.2-321635 as a highly polarized transient point source with the Australian SKA Pathfinder. ApJ, in the press; arXiv: 2109.00652
