Testing for synchrotron self-absorption in GRB 970111

Abstract

The time-resolved spectra of several gamma-ray bursts have shown that near the beginning of the burst, some absorption mechanism makes the spectra inconsistent with the simple optically-thin synchrotron shock model. We fit GRB 970111, which shows strong evidence for such absorption, with a synchrotron shock spectra suffering self-absorption. The synchrotron self-absorption shape does fit the BATSE time-evolving spectra, although it may be inconsistent with BeppoSAX WFC data. If the turnover just below the spectral break is due to synchrotron self-absorption, a magnetic field strength of 4 107 G is required.