TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3842
SUBJECT: GRB 050820B: Swift XRT position
DATE:    05/08/21 03:26:35 GMT
FROM:    David Burrows at PSU/Swift  <dxb15@psu.edu>

D. N. Burrows (PSU) reports on behalf of the Swift XRT team:

The Swift BAT instrument triggered on GRB 050820B at 23:50:27.19 UT (GCN 
3839, Page et al.).  At that time, the source was within the Earth limb 
constraint and the S/C was not able to slew immediately.  Swift executed a 
delayed slew at 0:17:37, while the observatory was in the South Atlantic 
Anomaly.  The XRT attempted to locate a bright source in its field of view, 
but was not able to do so due to the delayed slew and to the presence of 
many charged particle events in the image.  XRT Photon-Counting mode 
observations began at 00:28:3.6 (2256 s after the burst trigger), following 
exit from the South Atlantic Anomaly and completion of pre-programmed XRT 
engineering data collection.   In analysis of engineering format (PASS1) 
ground-processed data at the MOC, we find a faint, fading, uncataloged 
X-ray source located at:

RA(J2000) = 09h 02m 24.6s
Dec(J2000) = -72d 38' 43"

with an estimated uncertainty of 8 arcseconds (90% containment 
radius).  This position is 25 arcseconds from the refined BAT position 
reported in GCN 3840 (Fenimore et al.).

Further observations are in progress.  Refined analysis will become 
available following processing of the data through the Swift Data Center's 
pipeline.