Prompt optical observations of GRB 050319 with the swift UVOT

Abstract

The UVOT telescope on the Swift observatory has detected optical afterglow emission from GRB 050319. The flux declined with a power-law slope of α = -0.57 between the start of observations some 230 s after the burst onset (90 s after the burst trigger) until it faded below the sensitivity threshold of the instrument after ∼5 × 10⁴ s. There is no evidence for the rapidly declining component in the early light curve that is seen at the same time in the X-ray band. The afterglow is not detected in UVOT shortward of the B band, suggesting a redshift of about 3.5. The optical V-band emission lies on the extension of the X-ray spectrum, with an optical-to-X-ray slope of β= -0.8. The relatively flat decay rate of the burst suggests that the central engine continues to inject energy into the fireball for as long as a few × 10⁴ s after the burst. © 2006. The American Astronomical Society. All rights reserved.