The giant Metrewave Radio Telescope (GMRT) in Pune has facilitated the first detection of a bright transient celestial object, found moving at half the speed of light (3 multiplied by 10^8 metre per second).
This is only the first discovered Fast Blue Transient Object (FBOT) in the radio frequency wavelength, showing presence of hydrogen.
Transients are luminous celestial objects that usually brighten up and go dim in the sky within a short period of time. The lighting up is the ejection of emissions or energy from the source, either an event like the explosion of stars or mergers of neutron stars, among others.
There are only three known FBOTs to date. The object named CSS161010 involved in the present discovery happens to be the fastest moving by far to have been detected by scientists.
“There must be some powerful source emanating such vast amounts of energy, which is driving the explosion at such high speeds. This is an unusual stellar explosion and seems to be a completely new species of celestial objects of which we do not know much at this point in time,” said Deanne Coppejans, a post-doctoral fellow at Northwestern University, USA. She is a part of the discovery team along with researchers from TIFR-National Centre for Radio Astrophysics (NCRA) that operates the GMRT.
The transient object was first detected in 2016 in the optical wavelength, immediately followed up by observations in X-Ray and radio frequencies. This is where the GMRT came into picture.
Using the GMRT observation prior to the telescope’s recent upgrade, NCRA researchers Poonam Chandra and A J Nayana observed CSS161010 thrice in radio frequency.
“The GMRT took up observations between day 343 and 350 after it was first detected. Even after one year into its journey, the transient maintained 40 per cent speed that of light,” Nayana said.
Though data from Karl G Jansky Very Large Telescope (VLA) and Chandra X-Ray Telescope were involved in this study, it is the low frequency range offered by the GMRT that gave researches an edge in making this discovery.
The time taken by this transient to flare up in the sky, when observed in the optical wavelength, was about four days. Later, within a few days, it burnt out completely, giving a tiny window to scientists for carrying out observations.
Prof Chandra said, “Generally, as time passes, the explosion goes low on energy and becomes even more difficult to detect. Had it not been for the low frequency range offered by the GMRT, calculating its varying speed would not have been possible.”
The transient belongs to a tiny galaxy with mass lesser than that of the Milky Way, making it extremely rare, Coppejans said.
“The observations prove the most luminous FBOTs have a ‘central engine’ – a source like a neutron star or black hole that powers the transient. It could be from a class of transients rich in hydrogen,” said co-researcher R Margutti, also from Northwestern.
Despite being surrounded by a dense environment, the transient object, located 500 million light years away, managed to remain at a very high speed.
“The ejecta waded through thick environment of matter and showed traces of hydrogen. It indicates that the source could be a massive star that has substantial amount of hydrogen still intact inside, all of which was getting exploded,” Chandra added.
The research team is, however, yet to calculate the amount of hydrogen.
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