Radio emission of the cosmic gamma-ray burst GRB 080319B: Observations of the afterglow using telescopes of the Institute of Applied Astronomy of the Russian Academy of Sciences

Results of radio observations of the cosmic gamma-ray burst GRB 080319B at 8.45 GHz during the afterglow are reported. The observations were carried out on telescopes of the Zelenchukskaya and Svetloe Observatories of the Institute of Applied Astronomy, Russian Academy of Sciences. Two outbursts in the radio brightness were detected in the afterglow of GRB 080319B. A total of 148 radio observations were performed at 3.5, 6.2, and 13 cm. The observations were conducted in a mode with smooth scanning in elevation, which was also used to update the flux densities of the primary reference sources. The first powerful radio outburst was recorded on March 28, 2008, 6.86d after the gamma-ray burst, when the maximum flux density was F 8.45 GHz = 44 ± 12 mJy. Almost two months later, a second increase in the radio brightness was observed. The flux density monotonically increased from 19 mJy (59.55d) to 34mJy (59.79d) over 6.5 h; 1.17 d later, the flux density fell to 12mJy.At this last epoch, the radio flux demonstrated variability within 3σ on timescales of 9d−10d. The detected radio brightness increases are interpreted in terms of MHD interactions of a fast plasma outflow with a cloud of inhomogeneous surrounding medium. This interaction is accompanied by restructuring of the relativistic plasma outflow; the analysis of this process has been carried out.