Prompt optical observations of GRB050319 with the Swift UVOT

TL;DR

This paper reports optical observations of GRB 050319 using Swift UVOT, revealing a steady decay of the afterglow without early rapid decline, and suggests ongoing energy injection from the central engine.

Contribution

First optical afterglow detection of GRB 050319 with detailed light curve analysis, indicating prolonged energy injection and a redshift around 3.5.

Findings

Optical afterglow decays with a power law slope of -0.57.

No early rapid decline component in optical, unlike in X-ray.

Optical to X-ray spectral slope of -0.8.

Abstract

The UVOT telescope on the Swift observatory has detected optical afterglow emission from GRB 050319. The flux declines with a power law slope of alpha = -0.57 between the start of observations some 230 seconds after the burst onset (90s after the burst trigger) until it faded below the sensitivity threshold of the instrument after ~5 x 10^4s. 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 beta = -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 x 10^4s after the burst.