Oganesyan G., Karpov S., Beskin G., Ivanov E., Perkov A., Lyapsina N. (SAO RAS) in cooperation with O. Salafia (INAF-OAB), M. Jelínek (ASU CAS), S. Ronchini (GSSI), B. Banerjee (GSSI), M. Branchesi (GSSI), J. Štrobl (ASU CAS), K. Polášek (ASU CAS), R. Hudec (ASU CAS), E. Katkova (RPC ``PSI``, JSC), A. Biryukov (SAI MSU), V. Sasyuk (KFU), M. Mašek (CEICO), P. Janeček (CEICO), J. Ebr (CEICO), J. Jurišek (CEICO), R. Cunniffe (CEICO), M. Prouza (CEICO)

    In the night of June 19-20, 2021, the 9-channel Mini-MegaTORTORA (MMT-9) system detected a bright (~10 magnitude) optical flare that accompanied one of the most powerful and distant (at a distance of 10 billion light years) gamma-ray bursts GRB 210619B. Its emission was observed simultaneously by four MMT-9 lenses with the 1, 5, 10, and 30 seconds temporal resolution in white and green (V band) light. Somewhat earlier, this event was detected by the telescopes: D50 of the Czech Academy of Sciences (Ondřejov) and FRAM-ORM (La Palma) with a temporal resolution of 10 and 20 seconds, respectively. The high temporal resolution in the MMT-9 observations made it possible to compare the fine temporal structure of the gamma-ray burst GRB 210619B itself with its behavior in the optical range. And if the hard radiation was a set of bursts of the second duration, then such details were reliably absent in the synchronous optical light curve, which for the first time became direct evidence of the implementation of the “reverse shock” model in the burst. This conclusion was supported by the peculiarities of the optical spectrum evolution of GRB 210619B discovered during the simultaneous detection of its radiation by the MMT-9, D50, and FRAM-ORM detectors in various intervals of the optical range. The unique data obtained in this study, combined with the results of observations of the Swift and Fermi gamma-ray telescopes, and based on the theoretical analysis carried out jointly with a group of Italian astrophysicists (GSSI, INFN, INAF, and UNIMIB) have allowed us to establish that out of 900 gamma-ray bursts with optical companions of GRB 210619B is clearly associated with a narrow ejection of matter during the collapse of a massive star propagating in a very rarefied interstellar medium at almost the speed of light, and its optical emission is due to the shock wave generated, when this ejection collides with the interstellar gas and moving in the opposite direction to the source of gamma-burst.

Fig. 1. Results of observations of GRB 210619B in the optical and gamma ranges. Top panel shows the light curves. The bottom panel shows the evolution of the spectrum in the initial stage of generation of the object's radiation.

The work was carried out within the framework of the grant from the Ministry of Science and Higher Education of the Russian Federation № 075-15-2022-262 (13.MNPMU.21.0003)

Published:
Oganesyan G., Karpov S., Salafia O.S., Jelínek M., Beskin G., Ronchini S., Banerjee B., Branchesi M., Štrobl J., Polášek C., Hudec R., Ivanov E., Katkova E., Perkov A., Biryukov A., Lyapsina N., Sasyuk V., Mašek M., Janeček P., Ebr J., Exceptionally bright optical emission from a rare and distant gamma-ray burst, 2023, Nature Astronomy, Volume 7, p. 843-855
DOI: 10.1038/s41550-023-01972-4