X-ray variability of the afterglow from GRB970828 Original Research Article

A gamma-ray burst of 28 August 1997 (GRB970828) was localized by the All-Sky Monitor on the Rossi XTE satellite soon after the GRB. ASCA made a quick followup observation receiving the burst alert from RXTE, and detected a fading X-ray afterglow in its error ☐. Because of its quickness the afterglow was still rather bright (∼ 5 × 10−13 ergs cm−2s−1 : 2−10 keV), and ASCA obtained the data of good quality. Its light curve displays significant variation while the entire data appears to be consistent with a simple decay represented by t−1.4 considering together the flux given by the PCA/RXTE scan at an earlier period. We found the spectral features of the absorption due to the matter presumably near the GRB, which implies an uncorrected column depth of 4.1 × 1021 cm−2.