[vsnet-grb-info 24796] GRB 200127A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26895
SUBJECT: GRB 200127A: Swift detection of a burst
DATE:    20/01/27 15:04:17 GMT
FROM:    Caryl Gronwall at PSU/Swift-UVOT  <caryl at swift.psu.edu>

M. J. Moss (GWU), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), C. Gronwall (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 14:44:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200127A (trigger=952791).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 295.204, +44.910 which is 
   RA(J2000) = 19h 40m 49s
   Dec(J2000) = +44d 54' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the available
BAT light curve shows no significant structure. 

The XRT began observing the field at 14:46:52.1 UT, 140.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 295.19447,
44.90030 which is equivalent to:
   RA(J2000)  = 19h 40m 46.67s
   Dec(J2000) = +44d 54' 01.1"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 42 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 consistent with the Galactic value of 2.17
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 9.40e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
309 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 100% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. 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 18.0 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. J. Moss (mikejmoss3 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/)