GCN Circular 34110

CRESSTII), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:

At 22:26:10 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 230628E (trigger=1177054).  Swift slewed immediately to the burst.  The BAT on-board calculated location is 
RA, Dec 171.841, -11.447 which is 
   RA(J2000) = 11h 27m 22s
   Dec(J2000) = -11d 26' 47"
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 ~600 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 22:29:48.3 UT, 217.7 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 171.8499, -11.4641 which is equivalent to:
   RA(J2000)  = +11h 27m 23.77s 
   Dec(J2000) = -11d 27' 50.2”
with an uncertainty of 1.9 arcseconds (radius, 90% containment).  This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper.  No spectrum from the
promptly downlinked event data is yet available to determine the column density.

UVOT took a finding chart exposure of 150 seconds with the White filter starting 221 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 XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT 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 0.040.

Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu). 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/)