GCN Circular 2901
Subject
GRB041223: Swift XRT Detection of X-ray Afterglow Emission
Date
2004-12-24T05:41:36Z (19 years ago)
From
David Burrows at PSU/Swift <burrows@astro.psu.edu>
D. N. Burrows, J. E. Hill, J. Racusin, J. Kennea, D. Morris, J. A. Nousek
(PSU), G. Chincarini, G. Tagliaferri, A. Moretti, P. Romano, S. Campana, D.
Malesani, C. Pagani (OAB), A. Wells, J. Osborne, A. Beardmore, K. Page (U.
Leicester), P. Giommi (ASI), M. Chester (PSU), S. Barthelmy, N. Gehrels, N.
White (GSFC), K. Mason (MSSL), on behalf of the Swift XRT team.
The Swift X-Ray Telescope (XRT) was pointed at GRB041223 (GCN 2898, Tueller
et al.) on 2004/12/23 at 18:43:59 UT for 1490 s, at 20:16:24.4s for 1600 s,
and at 21:50:40 for 430 s. The spacecraft did not autonomously slew to the
burst since automated slewing is not yet enabled and the XRT is in the
midst of engineering measurements. The observation was performed as a
Target of Opportunity beginning about 4.5 hours after the burst.
We detect a fading X-ray source about 3.5 arcminutes from the BAT
position. The ground-calculated positions were checked through two
independent data processing and analysis techniques, which yielded
consistent sky positions within 22 arcseconds. Our best estimate of the
X-ray afterglow position is 06:40:49.2, -37:04:21.5 (J2000) for the first
observation. The position determined independently for the second
observation was within 4 arcseconds of these coordinates. The XRT
alignment is not yet fully calibrated, and we estimate a systematic
uncertainty of about 15 arcseconds in this position. Checks against
SIMBAD, DSS and X-ray catalogs from ROSAT, ASCA, XMM, and Chandra yielded
no known source at this position on the sky.
We have a total of about 580 counts from this object in the first two
observations. A simple power-law fit to the spectrum gives a photon index
of 1.43 +/- 0.09 and model fluxes of 1.7E-12 ( 0.5-2 keV) and 4.7E-12 (2-10
keV) ergs/cm**2/s. We caution that the instrument is not yet fully
calibrated and that these fluxes may have systematic uncertainties of
15%. The light curve based on all three observations is well fit with a
power-law index of 2.2 +/- 0.3.