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GCN Circular 34981

GRB 231111A: Swift detection of a burst with an optical counterpart
2023-11-11T14:33:33Z (6 months ago)
Jamie Kennea at Penn State <>

A. Melandri (INAF-OAR), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), S. Dichiara (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU) and D. M. Palmer (LANL) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 14:17:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 231111A (trigger=1195887).  Swift slewed immediately to
the event. The BAT on-board calculated location is 
RA, Dec 290.234, +52.447 which is 
  RA(J2000) = 19h 20m 56s
  Dec(J2000) = +52d 26' 49"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a telemetry outage, there is no
immediately available BAT lightcurve information.  However the
trigger information indicates an initial count rate of
3100 counts/s (25-100 keV) on a 1 second timescale. 

The XRT began observing the field at 14:18:59.3 UT, 99.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 290.1915, 52.4383 which is equivalent to:
   RA(J2000)  = 19h 20m 45.96s
   Dec(J2000) = +52d 26' 17.9"
with an uncertainty of 5.5 arcseconds (radius, 90% containment). This
location is 98 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 238 seconds with the U filter starting
164 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	19:20:45.24 = 290.18848
  DEC(J2000) = +52:26:10.5  =  52.43626
with a 90%-confidence error radius of about 0.62 arc sec. This position is 9.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.51 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.117. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT 
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:

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