Prompt Optical Detection of GRB 050401 with ROTSE-IIIa

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Published 2005 September 19 © 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation E. S. Rykoff et al 2005 ApJ 631 L121 DOI 10.1086/497370

1538-4357/631/2/L121

Abstract

The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected prompt optical emission from Swift GRB 050401. We present observations of the early optical afterglow, first detected by the ROTSE-IIIa telescope 33 s after the start of γ-ray emission, contemporaneous with the brightest peak of this emission. This GRB was neither exceptionally long nor bright. This is the first prompt optical detection of a GRB of typical duration and luminosity. We find that the early afterglow decay does not deviate significantly from the power-law decay observable at later times and is uncorrelated with the prompt γ-ray emission. We compare this detection with the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All three bursts exhibit quite different behavior at early times.

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10.1086/497370