Compton Cooling in the Afterglows of Gamma‐Ray Bursts: Application to GRB 980923 and GRB 971214

The role of Compton cooling in the standard model for the afterglows ofgamma-ray bursts is considered. When electrons cool by scattering off their ownsynchrotron photons, three cooling regimes are identified in which the observedsynchrotron radiation exhibits qualitatively different characteristics.Depending on the values of the source parameters, an afterglow may evolvethrough one, two or all three of these regimes. Since synchrotron radiation canbe regarded as Compton scattering of the virtual photons due to the magneticfield, in one of these regimes the instantaneous synchrotron spectrum hasproperties identical to those when Compton cooling is negligible. During thisphase in the evolution, the synchrotron radiation falls mainly in the nearinfrared/optical/UV spectral range. It is argued that the observed afterglowsof GRB 980923 and GRB 971214 are outside this degenerate phase. The derivedvalues of the source parameters show Compton cooling to have been important inboth of these afterglows.Comment: 23 pages, 4 figures, ApJ in pres