Early-Time Optical Spectral Shape Measurements of GRB 200925B

Z. Abdullayev, Toktarkhan Komesh, B. Grossan, Ernazar B. Abdikamalov, Zhanat Maksut, M. Krugov, Shynaray Myrzakul, D. Tuiakbayeva, A. Kostangeldinova

2025

Full text Open access: Gold Metadata (CSL-JSON)

DOI 10.22201/ia.14052059p.2025.59.20

Data confidence 70 medium

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Abstract

Optical broad-band spectral shape measurements of gamma-ray bursts (GRBs) are typically made starting an hour or more after the trigger event. With our automated, rapid-response system, the Burst Simultaneous Threechannel Imager (BSTI) on the Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO), we began measurements of GRB 200925B 129 s after the Swift BAT trigger. The temporal decay log slopes in the g', r', and i' bands in the time interval 129 s to 1029 s are -0.43 0.31, -0.43 0.15, and -0.72 0.14, respectively. During the decay phase, a shift in color from red to blue, a change in log slope of β from -2.73 to -1.52 was measured. The evolution in the optical spectral slope is consistent with a decrease in extinction caused by dust destruction.