Swift Identification of Dark Gamma-Ray Bursts

Abstract

We present an optical flux vs. X-ray flux diagram for all known gamma-ray bursts (GRBs) for which an X-ray afterglow has been detected. We propose an operational definition of dark bursts as those bursts that are optically subluminous with respect to the fireball model, i.e., which have an optical-to-X-ray spectral index beta_OX < 0.5. Out of a sample of 52 GRBs we identify 5 dark bursts. The definition and diagram serve as a simple and quick diagnostic tool for identifying dark GRBs based on limited information, particularly useful for early and objective identification of dark GRBs observed with the Swift satellite.

4 pages, 1 figure. ApJ Letters, in press

References in corpus (2)

• Optical Photometry of GRB 021004: The First Month
• The afterglow and complex environment of the optically dim burst GRB 980613

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