A Large Catalogue of Multi-wavelength GRB Afterglows I: Color Evolution And Its Physical Implication

摘要: The spectrum of gamma-ray burst (GRB) afterglows can be studied with color indices. Here we present a large comprehensive catalogue 70 GRBs multi-wavelength optical transient data on which perform systematic study to find the temporal evolution We categorize them into two samples based how well indices are evaluated. Golden sample includes 25 bursts mostly observed by GROND, and Silver 45 other telescopes. For sample, that 95\% do not vary over time. However, during short periods in most bursts. variations consistent effects (i) cooling frequency crossing energy bands wind medium (43\%) constant density (30\%), (ii) early dust extinction (12\%), (iii) transition from reverse shock forward emission (5\%), or (iv) an emergent supernova (10\%). also evolutionary properties mean for different episodes. 86\% show constancy between consecutive ones. index occur mainly late GRB-SN bump, flare reversed-shock components. further statistical analysis various observational model parameters (spectral $\beta_{o}^{\rm CI}$, electron spectral $p^{\rm etc.) using Overall, conclude $\sim$ 90\% colors time accounted simplest external model, while varying call more detailed modeling.