GCN Circular 3087
Subject
Swift-BAT trigger 107873: No Swift XRT counterpart
Date
2005-03-11T18:34:58Z (21 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
D. Malesani, A. Moretti, P. Romano, G. Tagliaferri, S. Campana, G.
Chincarini (INAF-OAB), V. La Parola, T. Mineo (INAF-IASF/Palermo), A. P.
Beardmore, O. Godet (U. Leicester), M. Capalbi, M. Perri (ASDC), J. A.
Kennea, D. Grupe, D. N. Burrows (PSU), S. Barthelmy, L. Barbier, N. Gehrels
(GSFC), J. Cummings (GSFC/NRC) report on behalf of the Swift XRT and BAT teams:
The Swift X-ray Telescope (XRT) re-observed the field of BAT trigger 107873
(also referred to as GRB050309; Barthelmy et al., GCN 3082), starting on
2005 Mar 9 at 19:46:51 UT. Observations ended on 2005 Mar 10 at 9:10:40 UT,
with a net exposure time of 15.7 ks distributed over 9 orbits. (The first
observation, reported in GCN 3082, was for 4ks). We report here the
analysis of the second epoch data for the two possible X-ray sources
discussed in GCN 3082 (Barthelmy et al.).
Source #1 is confirmed to be a real object, and its flux increased since
our previous observation by a factor of ~2. Its refined coordinates are:
RA(J2000) = 12:10:31.1, Dec(J2000) = +77:37:04.4. This object coincides to
within 1.4 arcsec with a USNO star with R~13.5, B~15.4. Its X-ray spectrum
is very soft, well described by a power law with photon index Gamma = 3.2
+- 0.3. The properties of this object are consistent with those of a
Galactic coronal source.
With the additional data, it is now apparent that source #2 is an
instrumental artifact.
Therefore, given the absence of any X-ray counterpart, and the low
significance of the BAT detection, we conclude that this BAT trigger is
unlikely to be a real GRB event.