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GCN Circular 34894

GRB 231028A: Swift detection of a burst
2023-10-28T04:28:17Z (7 months ago)
David Palmer at LANL <>

M. A. Williams (PSU), S. Dichiara (PSU), D. M. Palmer (LANL),
T. Sakamoto (AGU) and B. Sbarufatti (INAF-OAB) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 04:09:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 231028A (trigger=1193078).  Swift did not slew to the 
GRB location due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 214.029, +20.895 which is 
   RA(J2000) = 14h 16m 07s
   Dec(J2000) = +20d 53' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex peak
structure with a duration of at least 18 sec, although the immediately
available data is truncated at T+8s due to packet loss. The peak count
rate was ~8500 counts/sec (15-350 keV), at ~1 sec after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 15:45 UT on 2023 November 22. There will thus be no XRT
or UVOT data for this trigger before this time. 

Swift Triggers have recently been re-enabled while we are dealing
with attitude problems that can lead to star tracker Loss-of-Lock (LoL). 
We are confident that this GRB was not caused by an LoL event because:
1) The Swift_BAT_Position notice did not indicate a LoL. 
  (See the comments section.)
2) This burst location was not near to a known bright source. 
3) There was a simultaneous trigger by Fermi-GBM. 
4) This is a rate-triggered burst on a 1.024 s timescale, while most LoL
false triggers have been 'Image Triggers' with duration 64 s and longer. 

Observers should continue to be cautious (especially checking the
comments for LoL) in future GCN notices going forward. 

Burst Advocate for this burst is M. A. Williams (mjw6837 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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