[vsnet-grb-info 22814] Swift Trigger 912102: possible GRB 190630B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24913
SUBJECT: Swift Trigger 912102:  possible GRB 190630B
DATE:    19/06/30 06:24:47 GMT
FROM:    Hans Krimm at NSF/NASA-GSFC  <hkrimm at nsf.gov>

H. A. Krimm (NSF), N. J. Klingler (PSU), K. L. Page (U Leicester) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 06:02:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 190630B (trigger=912102).  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 223.669, +41.521 which is 
   RA(J2000) = 14h 54m 41s
   Dec(J2000) = +41d 31' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 5 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger. 
This increase in flux occurred during a rise in background due to
entry to the SAA, so it is not immediately clear from the BAT data 
alone that this is indeed a burst rather than a noise event. 

The XRT began observing the field at 06:03:10.7 UT, 62.1 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of  66 seconds with the White filter
starting 65 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 expected extinction corresponding to E(B-V) of
0.01. 

Due to the high background in the BAT and the lack of immediate
counterpart detection in the XRT, the Swift team will not be able to
confirm or deny whether this event is a GRB without further data. 

Burst Advocate for this burst is H. A. Krimm (hkrimm AT nsf.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/)