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GCN Circular 27638

Subject
GRB 200425A: Swift detection of a burst
Date
2020-04-25T00:40:11Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), M. J. Moss (GWU), D. M. Palmer (LANL),
T. Sbarrato (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 00:16:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200425A (trigger=967774).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 85.241, -13.459 which is 
   RA(J2000) = 05h 40m 58s
   Dec(J2000) = -13d 27' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The immediately-available BAT light curve
data only extends to T+8s, at which time the GRB was still active
with a multi-peaked structure.  The peak count rate up to that time
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 00:17:52.2 UT, 90.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 85.2198, -13.4352 which
is equivalent to:
   RA(J2000)  = 05h 40m 52.76s
   Dec(J2000) = -13d 26' 06.8"
with an uncertainty of 2.9 arcseconds (radius, 90% containment). This
location is 113 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
https://www.swift.ac.uk/sper.  We cannot determine whether the source
is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.59
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 93 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 0.16. 

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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