Using the Giant Metrewave Radio Telescope (uGmrt), in India, two scientists discovered that At 2018 – also known as “the cow” – presents an extremely inhomogeneous environment. This is the first observational evidence of inhomogeneous emission from an Fbot. All the details on ApJ Letters
Two astronomers from the National Center for radio Astrophysics at the Tata Institute of Fundamental Research (Ncra-Tifr) in Pune, using the Giant Metrewave Radio Telescope (uGmrt), found that At 2018 – for friends, the cow – presents an extremely inhomogeneous environment. . This object is the first of a class of recently discovered cosmic explosions known as Fast Blue Optical Transient (Fbot). They are sources that release an enormous amount of energy but which vanish very quickly. This, together with their extremely blue color, led to them being called Fbots. The discovery, published in The Astrophysical Journal Letters, represents the first observational evidence of inhomogeneous emission of an Fbot . The origins of Fbots are still under discussion, but proposed models include the explosion of a massive star, the collision of an accreting neutron star with another star, or the merger of two white dwarfs .
Precisely because they appear and disappear very quickly, Fbots are difficult to find. Many of them have been discovered in recent years thanks to the advent of surveys that scan the sky almost daily. Fbots that also emit in radio are even rarer, but they are particularly interesting because radio observations help determine the properties of the environments of these explosions and their ancestors.
At 2018cow was discovered on June 16, 2018. At a distance of about 215 million light years, “the cow” showed much greater brightness than normal supernovae . The two authors of the study, Poonam Chandra and AJ Nayana , carried out radio observations of At 2018cow with the uGmrt to determine the properties of its extended environment and region of emission. “Our studio benefited enormously from the uGmrt’s unique low frequency capabilities. The cow’s uGmrt observationsthey played a unique role in highlighting the non-uniform density around this explosion, ”explains Nayana, adding:“ Our work provides the first observational evidence of inhomogeneous emission from an Fbot. The density of the material around this explosion drops dramatically to around 0.1 light-years from the transient. This indicates that the progenitor star of At 2018cow, towards the end of its life cycle, was losing mass much faster ».
At 2018cow is also unusual because it has been on the radio for a long time. The longer the post-explosion emission can be observed, the greater the distance traveled by the ejected material during the explosion. This allows studying the source environment on a large scale. The authors observed the cowfor about 2 years with the uGmrt, to understand its properties. “This is the first Fbot seen for so long at low radio frequencies and the uGmrt data has provided crucial information about the environment of this transient,” continues Nayana. “That’s the beauty of low-frequency radio observations: you get to trace the footprints of the parent system long before it explodes. It is interesting that the material of the explosion moves with a speed greater than 20 percent of the speed of light even after about 257 days after the explosion, without any deceleration, ”adds Poonam Chandra.
While the origin of Fbots is still under debate, detailed radio observations can provide some insight into various physical parameters of these events, such as the speed of the material that escaped from this explosion, the strength of the magnetic field, and the rate at which the parent system loses. mass before the explosion. UGmrt observations from At 2018cow suggest that the progenitor ejected its material about 100 times faster during the years near the end of its life than it did about 23 years before the explosion. Furthermore, At 2018cow showed inhomogeneity in the radio emission region while the other two radio Fbots did not show these properties, making the cowunique in its group. “The observations of multiple Fbots with the uGmrt will provide information on their environments and ancestors, to develop a complete picture of the properties of these intriguing transients,” concludes Nayana.
Featured image: Artist’s impression of a fast and blue optical transient. Credits: Bill Saxton, Nrao / Aui / Nsf
To know more:
- Read on The Astrophysical Journal Letters the article ” uGMRT Observations of a Fast and Blue Optical Transient — AT 2018cow ” by Nayana AJ and Poonam Chandra
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