![]() Ziteng Wang – PhD researcher, University of Sydney.It is just the first of many unusual transient sources that we expect to find with the powerful ASKAP array, and it gives a hint of the future of radio astronomy. We will keep observing this source in new ways. And even the known GCRTs exhibit diversity, and may not share a common origin. We don’t know what they are, but they are imaginatively called Galactic Center Radio Transients (GCRTs).Īre they related to ASKAP J173608.2-321635? There are some similarities, but there are also differences. Is the source’s proximity to the center of our galaxy a clue? Over the past 15 years, a number of intriguing radio sources have been discovered toward the Galactic center (including one dubbed the “cosmic burper”). But the characteristic of pulsars is rapid pulses between milliseconds to seconds long, and we did not detect these with Parkes or MeerKAT. What can we say about what it actually is?Ĭan it be a star? It seems unlikely because stars also emit much of their light in the optical and infrared (like the Sun), but we detect nothing at these wavelengths.Ĭan it be a pulsar? Like our signal, pulsars produce polarised radio waves and can vary dramatically in brightness. We have observed this strange object at multiple wavelengths using telescopes on three continents and in space. Telescopes working at other wavelengths can serve as another pair of eyes to help us find new clues.Īfter the MeerKAT detection, we searched for the source in X-rays (using the space-based Neil Gehrels Swift Observatory and Chandra X-ray Observatory) and infrared (using the Gemini telescope in Chile). It is always a good idea to investigate from multiple perspectives. Radio lightcurve showing how ASKAP J173608.2-321635 varies with time. The source disappeared in the course of a single day, even though it had lasted for weeks in our previous ASKAP observations. ![]() Luckily, the signal returned, but the behavior of the source was now dramatically different. Because the signal was intermittent, we observed it for 15 minutes every few weeks, hoping we would see it again. We then tried the more sensitive MeerKAT radio telescope in South Africa. However, these observations yielded nothing. ![]() We next observed the source with the Parkes radio telescope in New South Wales to decide whether it was a pulsar. We need evidence to determine what it is.īased on our ASKAP data, we thought the new object might be a pulsar or a flaring star: both types of object can be polarised, and change in brightness. Investigating a new astronomical object is a bit like a detective job. Almost all of them are sources we understand well, such as pulsars (the rapidly rotating, highly magnetized remnants of exploded stars) or highly magnetized red dwarf stars. Polarised radio sources are extremely rare: we might find fewer than ten circularly polarised sources out of thousands. Our eyes cannot distinguish between polarized and unpolarized light, but ASKAP has the equivalent of polaroid sunglasses for radio waves. This behavior was extraordinary.Īs well as changing over time, the signal was circularly polarised. ![]() This object was unique in that it started out invisible, became bright, faded away, and then reappeared. ![]() When we looked towards the center of our galaxy (the Milky Way), we found a source we called ASKAP J173608.2-321635 (this catchy name comes from its coordinates in the sky). The small insets show the source turning off and on in images from the MeerKAT telescope. ASKAP image of the Galactic Centre region. ![]()
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