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GCN Circular 30501

Subject
GRB 210725A: Swift detection of a burst
Date
2021-07-25T04:07:21Z (3 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),
N. J. Klingler (GSFC/UMBC/CRESSTII), A. Y. Lien (GSFC/UMBC),
A. Melandri (INAF-OAB), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 03:47:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210725A (trigger=1061511).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 215.363, -1.177 which is 
   RA(J2000) = 14h 21m 27s
   Dec(J2000) = -01d 10' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 10 sec.  The peak count rate
was ~1800 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 03:48:53.6 UT, 110.7 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 215.3742,
-1.1934 which is equivalent to:
   RA(J2000)  = 14h 21m 29.81s
   Dec(J2000) = -01d 11' 36.2"
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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.09 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9
(+2.81/-2.40) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 114 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 0.046. 

Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.inaf.it). 
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/)
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