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Excited Si^+ and Fe^+ species are routinely observed in the host environment of gamma-ray burst (GRB) afterglows, but are not commonly seen in other extragalactic locations. Their presence signals unusual properties in the gaseous environment of these GRB hosts that arise either as a result of the intense ionizing radiation of the afterglow or through collision excitation in a dense cloud. In particular, the photon pumping scenario has explicit expectations for temporal variation in the strength of the excited lines, owing to the decline in the ionizing flux of the GRB afterglow. We analyze afterglow spectra of GRB 020813 obtained in two epochs of ~16 hours apart, and examine transitions from the first excited state of Fe^+ at J=7/2 in these two sets of data. We report a significant decline by at least a factor of five in the equivalent width of the FeII 2396 transition, the strongest from the J=7/2 state. We perform a Monte-Carlo analysis and determine that this temporal variation is present at more than 3sigma level of significance. This observation represents the first detection in the temporal variation of the excited Fe+ states in the GRB host ISM, a direct influence of the burst itself on its environment. We further estimate that the Fe^+ gas resides in 50-100 pc from the afterglow, based on the afterglow lightcurve and the presence and absence of the excited FeII 2396 in the two-epoch observations.
We report on the highly extinguished afterglow of GRB 070306 and the properties of the host galaxy. An optical afterglow was not detected at the location of the burst, but in near-infrared a doubling in brightness during the first night and later pow
We present a comprehensive temporal and spectral analysis of the long Swift GRB 120327A afterglow data to investigate the possible causes of the observed early time colour variations. We collected data from various instruments/telescopes in different
The afterglow of GRB 170817A has been detected for more than three years, but the origin of the multi-band afterglow light curves remains under debate. A classical top-hat jet model is faced with difficulties in producing a shallow rise of the afterg
We present the observations of the afterglow of gamma-ray burst GRB 090102. Optical data taken by the TAROT, REM, GROND, together with publicly available data from Palomar, IAC and NOT telescopes, and X-ray data taken by the XRT instrument on board t
In this work we present spectra of all $gamma$-ray burst (GRB) afterglows that have been promptly observed with the X-shooter spectrograph until 31-03-2017. In total, we obtained spectroscopic observations of 103 individual GRBs observed within 48 ho