In a first, uGMRT reveals patchy environment of a rare cosmic explosion

Published on May 02, 2021 09:45 PM IST

The scientists from the National Centre for Radio Astrophysics (NCRA) of the Tata Institute of Fundamental Research (NCRA-TIFR) Pune used the upgraded Giant Metrewave Radio Telescope (uGMRT) to determine that AT 2018 cow, the first of a newly discovered class of cosmic explosions has an extremely patchy environment

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The scientists from the National Centre for Radio Astrophysics (NCRA) of the Tata Institute of Fundamental Research (NCRA-TIFR) Pune used the upgraded Giant Metrewave Radio Telescope (uGMRT) to determine that AT 2018 cow, the first of a newly discovered class of cosmic explosions has an extremely patchy environment.

This is the first observational evidence of inhomogeneous emission from an FBOT. The origins of FBOTs are still under debate, but proposed models include explosion of a massive star, collision of an accreting neutron star and a star, merger of two white dwarfs.

The FBOT AT2018cow was discovered on June 16, 2018. At a distance of about 215 million lightyears, the ‘cow’ showed luminosities much greater than that of normal supernovae. Prof Poonam Chandra from NCRA-TIFR and Dr AJ Nayana, a former Ph.D. student of Prof Chandra both carried out radio observations of AT 2018cow with the uGMRT to determine the properties of its extended environment and emission region.

“Our study has tremendously benefited by the unique low-frequency capabilities of the uGMRT. The uGMRT observations of the ‘cow’ played a unique role in finding the non-uniform density around this explosion. Our work provides the first observational evidence of inhomogeneous emission from an FBOT. The density of the material around this explosion falls drastically around 0.1 light-year from the transient. This indicates that the progenitor star of AT2018cow was shedding mass much faster towards its end of life.” said Nayana.

AT 2018cow is also unusual in that it has been observable in the radio for a very long time. The longer one can observe the post explosion emission, the more distance the material that was ejected during the explosion has travelled. This allows one to study the large-scale environment of the source.

Both Dr Nayana and Prof Chandra have been observing the ‘cow’ for two years with the uGMRT to understand its properties.

“This is the first FBOT seen for this long at low radio frequencies and the uGMRT data gave crucial information about the environment of this transient. This is the beauty of low-frequency radio observations. One gets to trace the footprints of the progenitor system much before it exploded. It is interesting that the material from the explosion is moving with speed greater than 20 per cent speed of light even after ∼ 257 days post-explosion, without any deceleration.” said Prof Chandra.

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