[vsnet-grb-info 16231] Trigger 633105 is likely not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17512
SUBJECT: Trigger 633105 is likely not a GRB
DATE:    15/03/01 07:00:38 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien at nasa.gov>

A. Y. Lien (GSFC/UMBC), A. Maselli (INAF-IASFPA) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 06:20:54 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a source close to M31 (NGC224) (trigger=633105).  Swift slewed 
immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 11.332, +41.857 which is 
   RA(J2000) = 00h 45m 20s
   Dec(J2000) = +41d 51' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 06:22:32.4 UT, 98.3 seconds after
the BAT trigger. No source was detected in 604 s of promptly downlinked
data, which covered 91% of the BAT error circle. We are waiting for the
full dataset to detect and localise the XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 102 seconds after the BAT trigger. No new source has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the BAT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the expected extinction corresponding
to E(B-V) of 0.06. 

Given the lack of a bright XRT source and the proximity of the BAT
trigger to M31, it is possible that this is a noise event and not an
astrophysical source.  However, we note that the BAT image
significance is 8.75. The full ground-linked data set will be
necessary to verify. 

Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)