A&A 448, L9-L12 (2006)
DOI: 10.1051/0004-6361:200600007

Letter

A refined position catalogue of the Swift XRT afterglows

A. Moretti¹, M. Perri², M. Capalbi², L. Angelini^{3, 4}, J. E. Hill^{4, 5}, S. Campana¹, D. N. Burrows⁶, J. P. Osborne⁷, G. Tagliaferri¹, G. Cusumano⁸, P. Giommi², P. Romano¹, T. Mineo⁸, J. Kennea⁶, D. Morris⁶, J. Nousek⁶, C. Pagani^{1, 6}, J. Racusin⁶, A. F. Abbey⁷, A. P. Beardmore⁷, O. Godet⁷, M. R. Goad⁷, K. L. Page⁷, A. A. Wells⁷ and G. Chincarini<sup>1, 9

1</sup>  INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
    e-mail: moretti@merate.mi.astro.it
²  ASI Science Data Center, via G. Galilei, 00044 Frascati, Italy
³  NASA/Goddard Space Flight Center, Greenbelt Road, Greenbelt, MD 20771, USA
⁴  Department of Physics and Astronomy, Johns Hopkins University, 3400 Charles Street, Baltimore, MD 21218, USA
⁵  Universities Space Research Association, 10211 Wincopin Circle, Suite 500, Columbia, MD 21044-3432, USA
⁶  Department of Astronomy & Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
⁷  X-Ray Observational Astronomy Group, Department of Physics & Astronomy, University of Leicester, LE1 7RH, UK
⁸  INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica Sezione di Palermo, via U. La Malfa 153, 90146 Palermo, Italy
⁹  Università degli Studi di Milano-Bicocca, Dipartimento di Fisica, Piazza delle Scienze 3, 20126 Milano, Italy

(Received 18 November 2005 / Accepted 19 January 2006 )

Abstract
We present a catalogue of refined positions of 68 gamma ray burst (GRB) afterglows observed by the Swift X-ray Telescope (XRT) from the launch up to 2005 Oct. 16. This is a result of the refinement of the XRT boresight calibration. We tested this correction by means of a systematic study of a large sample of X-ray sources observed by XRT with well established optical counterparts. We found that we can reduce the systematic error radius of the measurements by a factor of two, from 6.5´´ to 3.2´´ (90% of confidence). We corrected all the positions of the afterglows observed by XRT in the first 11 months of the Swift mission. This is particularly important for the 37 X-ray afterglows without optical counterpart. Optical follow-up of dark GRBs, in fact, will be more efficient with the use of the more accurate XRT positions.

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© ESO 2006

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