Delayed Afterglow Onset Interpreted as Baryon-Poor Viewing Angle

Abstract

We have suggested previously that baryons in GRB fireballs infiltrate from the surrounding walls that collimate the fireball. The efficiency $\epsilon_b$ for generating blast energy can then be angle dependent. Delayed onset of afterglow can be interpreted as being due to a baryon-poor viewing angle.Comment: Submitted to ApJ Letters February 24, 200