Skip to main content
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 14699

Subject
Swift Trigger 556533 is probably not an astrophysical event
Date
2013-05-24T04:23:05Z (11 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
A. P. Beardmore (U Leicester), H. A. Krimm (CRESST/GSFC/USRA),
C. J. Mountford (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 04:03:55 UT, the Swift Burst Alert Telescope (BAT) triggered and
located trigger 556533.  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 118.580, -28.134 which is 
   RA(J2000) = 07h 54m 19s
   Dec(J2000) = -28d 08' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed no significant 
structure.  The peak count rate was ~1400 counts/sec (15-350 keV), 
at ~4 sec after the trigger. 

The XRT began observing the field at 04:05:29.5 UT, 94.7 seconds after
the BAT trigger. No source was detected in 574 s of promptly downlinked
data, which covered 92% 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 nominal 250.000 seconds with the
U filter  starting 154 seconds after the BAT trigger.  No credible
afterglow candidate has  been found in the initial data products. The
2.7'x2.7' sub-image covers 25% of  the BAT error circle. The typical
3-sigma upper limit has been about 19.6 mag.   The 8'x8' region for
the list of sources generated on-board covers 100% of the  BAT error
circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction 
expected. 

This was a marginal detection (5.85 sigma) in an image
at a location which was almost 12 arcminutes from
the known source A0753-2802.  Under these circumstances,
Swift attempts to verify or refute the reality of the
possible event using the narrow field instruments.  In
this case, we believe that this was due to a statistical
fluctuation and not an astrophysical event.
Looking for U.S. government information and services? Visit USA.gov