GCN Circular 3043

D. N. Burrows, J. E. Hill, J. A. Kennea, J. L. Racusin (PSU), C. 
Pagani,  A. Moretti (INAF-OAB), O. Godet, A. F. Abbey (U. Leicester), V. La 
Parola (INAF-IASF/Palermo), F. Tamburelli (ASDC), K. Hurley (UC-Berkeley), 
B. Zhang (U. Nevada), D. Hinshaw, L. Angelini, N. White, N. Gehrels (GSFC), 
report on behalf of the Swift XRT team:

CORRECTION: shortly after submitting this information to the GCN, we 
discovered an error in the XRT position.  The original rectangular error 
box based on WT mode data was correct, but the error circle based on image 
mode data was incorrect.  That position is corrected below.

The Swift BAT instrument detected GRB 050219b at 21:05:51 UT on 19 February 
2005.  The burst was too close to the Earth limb to allow immediate 
observation by the XRT and UVOT.  The observatory executed an automated 
slew to the BAT position at 21:56:25 UT and the XRT began taking data at 
about 21:58 UT.  The XRT was in Auto state and attempted to obtain a GRB 
position, but the source was too faint to obtain a reliable on-board 
centroid.  The ground-processed centroid of this image gives an approximate 
source position of:

CORRECTION:

RA(J2000) = 05:25:15.2
Dec(J2000) = -57:45:25.2

We estimate an uncertainty of 15 arcseconds in this position.

XRT then began observations in Windowed Timing mode, which provides 1-D 
position information.  There appears to be a fairly bright X-ray source at 
a position bounded by the following error box:

RA, Dec (J2000):
Corner #1: 05:25:44.9, -57:55:55.3
Corner #2: 05:25:44.2, -57:55:57.4
Corner #3: 05:24:41.7, -57:33:54.5
Corner #4: 05:24:41.0, -57:33:56.6

Photon-counting mode frames taken in the following orbit are expected to 
produce a more accurate position, and will be reported when they become 
available on the ground.