GCN Circular 2991

L. A. Antonelli (INAF-OAR), S. Campana, G. Tagliaferri, C. Pagani, A. 
Moretti, P. Romano, G. Chincarini (OAB), G. Cusumano, V. Mangano (ISAF/Palermo),
P. Giommi (ASI), D. N. Burrows, J. E. Hill, J. A. Kennea, J. Racusin,
J. A. Nousek (PSU), J. Osborne, K. Page, M. Goad, A. Beardmore,
A. Wells (U. Leicester), K. Mason (MSSL), N. White, N. Gehrels (NASA/GSFC),
report on behalf of the Swift XRT team:

The Swift BAT instrument detected an apparent burst at 04:20:04 UT on 2005 
January 28.  The spacecraft initiated a prompt automated slew and 
observation sequence.  The XRT began taking data on the burst at 2005-01-28 
04:23:51 and continued until 2005-01-28 05:55:27.  The XRT was in Photon 
Counting mode performing calibration observations of PG1311+129 when the 
burst occurred, and continued to collect data in Photon Counting mode 
during the slew and after settling onto the BAT field.  As a result, no 
prompt XRT position was reported to the ground.  However, analysis of the 
XRT data shows a bright, rapidly fading point source at:

RA(J2000): 14 38 17.87
DEC(J2000): -34 45 56.6

These positions were processed through the ground pipeline and have an 
estimated uncertainty of 8 arcseconds, dominated by systematic 
uncertainties in the XRT boresight, which is not yet fully calibrated.  We 
note, however, that our final position for GRB050126 was 30 arcseconds from 
the optical candidate (GCN 2985
Not found
 
 
) in spite of our estimated uncertainty of 8 
arcseconds.

The XRT count rate is 1.29+/-0.28 c/s (0.5-10 keV) in a 1745 s exposure, 
which corresponds roughly to a 1 mCrab source.

The XRT is continuing to observe this burst when it is visible to the Swift 
observatory.

[GCN OPS NOTE (28jan05):  Per D.Burrows request, the authors G. Cusumano, V. Mangano
were added to the list.]