Astronomers were able to find two relatives of a space “cow” — an unusually powerful transient AT2018cow in the constellation Hercules. The transients that have received designation ZTF18abvkwla (or “Koala”) and CSS161010 found in dwarf galaxies, and astronomers connect them with the formation or activity of black holes. Articles (1, 2) published in the journal The Astrophysical Journal.
Now the list of known FBOT with two new transients. The properties of the first, the designation ZTF18abvkwla (or “Koala”) and discovered in September 2018 as part of the review ZTF 1DC, researched by a team of astronomers, led by Anna Ho (Anna Ho) from the California Institute of technology. The results of the analysis of observations in x-ray and radio wavelengths of the second transient CSS161010 open in October 2016 in the framework of the related SRTS and ASAS-SN, has published another group of researchers headed by Dean Coppejans (Deanne Coppejans) from northwestern University.
Monitoring CSS161010 pointed to the intense flow of x-ray and radio emission, while the radio flux peaked approximately one hundred days into the outbreak, and then quickly began to subside. This is due to the collision of relativistic (0,55 speed of light) the outflow of the substance with a dense environment. Such outflow, in turn, is the result of an aspherical explosion is rich in hydrogen massive star followed by the formation of either a neutron star or a black hole. It is not excluded, however, the version tidal destruction of a star by a black hole of intermediate mass.
The behavior of the transient ZTF18abvkwla was similar with both AT2018cow and CSS161010. The observation data indicate rapidly rising and falling (for two to three days) intensive flux of visible radiation, and intensive flux of radiation that reaches a peak of 80 days after the start of the outbreak. Similar properties of transient is also considered to be the result of collisions of relativistic (0,38 speed of light) emission, possibly generated by a black hole, with a dense environment.
Another feature that combines two new transient, was that they were found in distant dwarf galaxies with a small level of metallicness. Further search for such transients, and their detailed study in various wavelength ranges should allow to understand physics of the processes leading to such events.