[vsnet-grb-info 16669] Swift Trigger 645340: a possible GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17950
SUBJECT: Swift Trigger 645340: a possible GRB
DATE:    15/06/21 12:01:59 GMT
FROM:    Frank Marshall at GSFC  <marshall at milkyway.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC), A. Y. Lien (GSFC/UMBC),
D. Malesani (DARK/NBI) and K. L. Page (U Leicester) report on behalf
of the Swift Team:

At 11:28:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located either Sco X-1 or a source near Sco X-1. Swift slewed 
immediately to the source. The BAT on-board calculated location is 
RA, Dec 245.071, -15.691 which is 
   RA(J2000) = 16h 20m 17s
   Dec(J2000) = -15d 41' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). The BAT position is 6.1 arcmin from 
Sco X-1. This was a 64 s image trigger with significance of 
17.7 sigma. As is usual with an image trigger, the available BAT 
light curve shows no significant structure. 

The source centroided on by the XRT is Sco X-1. This is, however, 363 arcsec 
from the BAT position, and thus outside the BAT error circle. We cannot 
determine at this time whether there is a new X-ray source within the BAT 
error circle. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 185 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 none of
the BAT error circle. The 8'x8' region for the list of sources
generated on-board covers 100% of the BAT error circle. No correction has
been made for the expected extinction corresponding to E(B-V) of 0.38. 

We await the full downlinked dataset to make a more definitive 
statement on the nature of this trigger. 

Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.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.)