[vsnet-grb-info 27341] GRB 210210A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29444
SUBJECT: GRB 210210A: Swift detection of a burst with an optical counterpart
DATE:    21/02/10 02:27:51 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

S. Laha (GSFC/UMBC/CRESST), J.D. Gropp (PSU), H. A. Krimm (NSF),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), B. Sbarufatti (PSU) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 02:00:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210210A (trigger=1031728).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 262.811, +14.648 which is 
   RA(J2000) = 17h 31m 15s
   Dec(J2000) = +14d 38' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a telemetry gap, only the first 
8 seconds of the BAT light curve after the trigger are available,
showing that the emission has at least two peaks and continues 
beyond that time.  The peak count rate
was ~6000 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 02:01:50.0 UT, 82.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 262.77059, 14.66385 which is equivalent
to:
   RA(J2000)  = 17h 31m 04.94s
   Dec(J2000) = +14d 39' 49.9"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 151 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (8.82 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.2
(+1.27/-1.18) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 85 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	17:31:05.00 = 262.77085
  DEC(J2000) = +14:39:45.8  =  14.66272
with a 90%-confidence error radius of about 1.10 arc sec. This position is 4.6
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.06. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.097. 

Burst Advocate for this burst is S. Laha (sib.laha AT gmail.com). 
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/)