Refined Astrometry and Positions for 179 Swift X-Ray Afterglows
Abstract
We present a refined catalog for the positions of 179 gamma-ray burst (GRB) X-ray afterglows observed by the X-Ray Telescope (XRT) on Swift prior to 2006 November 1. The positions are determined by detecting X-ray field sources in the deep X-ray images and comparing the centroids to those of optical sources in the Digitized Sky Survey red2 catalog or the Sloan Digital Sky Survey Data Release 5 catalog. Half of the 90% confidence error region radii are <2.2". The error regions areas are typically ~4 times smaller than the best XRT team error regions, although the positions require deep X-ray integration (>20 ks) and cannot be generated nearly as rapidly after the GRB. The positions derived for >90% of 77 bursts with optical afterglows are consistent with the optical transient positions, without the need for systematic error. About 20% of the afterglow positions require a sizable shift in the Swift satellite aspect. We discuss the optical/X-ray properties of the field sources and discuss the implications of the frame offsets for studies of optically dark GRBs.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 2007
- DOI:
- 10.1086/510836
- arXiv:
- arXiv:astro-ph/0611031
- Bibcode:
- 2007AJ....133.1027B
- Keywords:
-
- gamma rays: bursts;
- supernovae: general;
- telescopes;
- X-rays: general;
- Astrophysics
- E-Print:
- 8 pages, 5 figures, 3 tables, Accepted to AJ