Prompt, early and afterglow optical observations of five γ-ray bursts: GRB 100901A, GRB 100902A, GRB 100905A, GRB 100906A and GRB 101020A

Abstract

We present the results of the prompt, early and afterglow optical observations of five γ‐ray bursts (GRBs): GRB 100901A, GRB 100902A, GRB 100905A, GRB 100906A and GRB 101020A. These observations were made with the Mobile Astronomical System of TElescope‐Robots in Russia (MASTER‐II Net), the 1.5‐m telescope of the Sierra Nevada Observatory and the 2.56‐m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before the cessation of γ‐ray emission, at 113 and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted in two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. A more detailed analysis of GRB 100901A and GRB 100906A, supplemented by Swift data, provides the following results and indicates different origins for the prompt optical radiation in the two bursts. The light‐curve patterns and spectral distributions suggest that there is a common production site for the prompt optical and high‐energy emission in GRB 100901A. The results of the spectral fits for GRB 100901A in the range from optical to X‐ray favour power‐law energy distributions and a consistent value of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve, suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. We obtain an upper limit on the value of the optical extinction on the host of GRB 100906A.

The MASTER-II network of robotic optical telescopes. First results

“…The fundamental difference in the observed light curves and spectra for GRB 100901A and GRB 100906A [141] suggests that these two objects have a different physical nature. In the case of GRB 100901A, synchronous variations in all three bands (optical, X-ray, and gammaray) were observed (i.e., during the prompt emission); one example is the synchronous flare observed near 400 s. In contrast, the optical emission of GRB 100906A does not show any correlation with its harder emission.…”

“…Synchronous observations in the three ranges enable a good spectral analysis of the prompt emission, and the long series of observations revealed periodicity in the light curve. These results and the detailed photometry and spectral analysis of this GRB are published in [141].…”

“…This difference is supported by the spectral data. Allowing for the uncertainty in the optical absorption in the host galaxy, the spectrum of GRB 100901A can be described using a single power law from the optical to the gamma-ray, while, in the case of GRB 100906A, only the soft X-ray component may tentatively be correlated with the optical emission during the interval of prompt emission [141].…”

“…of GRB 100906A does not display any peculiarities in the first hours, and essentially corresponds to the light curve of an ideal GRB ( tailed information about the photometry and spectral information for GRB 100906A, and also a comparison with GRB 100901A, were published in [141].…”

“Lomonosov” Satellite—Space Observatory to Study Extreme Phenomena in Space

“…In this way, we plan to use successive experience of ground-based systems of wide field cameras and robotic telescopes of MASTER Global Robotic Net Kornilov et al 2012), which had detected the prompt emission of several GRBs (Gorbovskoy et al 2011(Gorbovskoy et al , 2016.…”