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Detection of color variability of the optical polarization of the blazar BL Lac
Considering the first results of X-ray polarimetry of blazars and extensive discussion on physical processes in relativistic jets of active nuclei, interest in multi-wavelength polarimetry of objects like BL Lac has now increased. This paper presents the results of multi-band optical observations of the well-known blazar BL Lac (z = 0.069) in polarized light obtained with the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 2020-2022. It is shown that the emission of the object, regardless of the phase of its activity, is characterized by intraday variability of brightness and polarization with changes occurring on a time-scale of up to 1.5 hours without any designated period. It is important that the polarization color shows variability on an hour scale. The observation results confirm that the object BL Laceratae exhibits the anti-correlation between brightness and degree of polarization that is qualitatively described by the shock-wave model in a turbulent jet plasma. For the first time, the dependence of the polarization color on the phase of the object activity was discovered, which indicates the dominance of different physical processes in the plasma and, together with the rapid variability of the polarization color, challenges modern numerical calculations.
Authors:
Shablovinskaya E.S., Malygin E.A., Oparin D.V. (SAO RAS)
Published:
Shablovinskaya E., Malygin E., Oparin D.; Chromatic optical polarization of BL Lac: while faint and bright, MNRAS, 519, 3, 3798-3810, 10.1093/mnras/stac3775 (2023)
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Detection and study of the optical flare that accompanied GRB 210619B, and the object model
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.
Authors:
Oganesyan G., Karpov S., Beskin G., Ivanov E., Perkov A., Lyapsina N. 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)
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
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