Swift XRT and VLT Observations of the Afterglow of GRB 041223

Abstract

The Swift Gamma-Ray Burst Explorer, launched on 2004 November 20, is a multiwavelength, autonomous, rapid-slewing observatory for gamma-ray burst (GRB) astronomy. On 2004 December 23, during the activation phase of the mission, the Swift X-Ray Telescope (XRT) was pointed at a burst discovered earlier that day by the Swift Burst Alert Telescope. A fading, uncataloged X-ray source was discovered by the XRT and was observed over a period of about 3 hours, beginning 4.6 hours after the burst. The X-ray detection triggered a VLT observation of the optical/NIR counterpart, located about 1.1 arcseconds from the XRT position. The X-ray counterpart faded rapidly, with a power law index of -1.72 +/- 0.20. The average unabsorbed X-ray flux 4.6-7.9 hours after the burst was 6.5 x 10^{-12} erg cm^{-2} s^{-1} in the 0.5-10 keV band, for a power-law spectrum of photon index 2.02 +/- 0.13 with Galactic absorption. The NIR counterpart was observed at three epochs between 16 and 87 hours after the burst, and faded with a power-law index of -1.14 +/- 0.08 with a reddening-corrected SED power-law slope of -0.40 +/- 0.03. We find that the X-ray and NIR data are consistent with a two-component jet in a wind medium, with an early jet break in the narrow component and an underlying electron index of 1.8-2.0.

arXiv comment16 pages, including 4 figures. Accepted by Astrophysical Journal (Letters) on 15 February 2005

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Cited by in corpus (9)

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• Swift observations of GRB050128: the early X-ray afterglow
• The Discovery of the Optical and Near-IR Afterglows of the First Swift Gamma-Ray Bursts
• Swift XRT Observations of the Breaking X-ray Afterglow of GRB 050318
• The multiwavelength afterglow of GRB 050721: a puzzling rebrightening seen in the optical but not in the X-ray
• United classification of cosmic gamma-ray bursts and their counterparts