Broadband observations of the afterglow of GRB 000926: Observing the effect of inverse Compton scattering

GRB 000926 has one of the best-studied afterglows to date, with multiple X- ray observations, as well as extensive multifrequency optical and radio cov erage. Broadband afterglow observations, spanning from X-ray to radio frequ encies, provide a probe of the density structure of the circumburst medium, as well as of the ejecta energetics, geometry, and physical parameters of the relativistic blast wave resulting from the explosion. We present an ana lysis of Chandra X-Ray Observatory observations of this event, along with H ubble Space Telescope and radio monitoring data. We combine these data with groundbased optical and IR observations and fit the synthesized afterglow light curve using models where collimated ejecta expand into a surrounding medium. We find that we can explain the broadband light curve with reasonab le physical parameters if the cooling is dominated by inverse Compton scatt ering. For this model, an excess due to inverse Compton scattering appears above the best-fit synchrotron spectrum in the X-ray band. No previous burs ts have exhibited this component, and its observation would imply that the GRB exploded in a moderately dense (n similar to 30 cm(-3)) medium, consist ent with a diffuse interstellar cloud environment.