TITLE:   GCN CIRCULAR
NUMBER:  26661
SUBJECT: GRB 200107B: Swift detection of a burst
DATE:    20/01/07 20:32:11 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@swift.psu.edu>

M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),
J. A. Kennea (PSU), N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),
S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), M. J. Moss (GWU),
K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU),
M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 19:26:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200107B (trigger=948219).  Swift did not slew immediately 
due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 107.066, -83.716 which is 
   RA(J2000) = 07h 08m 16s
   Dec(J2000) = -83d 42' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 80 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~35 sec after the trigger. 

The XRT began observing the field at 19:41:27.6 UT, 899.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 106.92567, -83.7189 which is
equivalent to:
   RA(J2000)  = 07h 07m 42.16s
   Dec(J2000) = -83d 43' 08.0"
with an uncertainty of 21.3 arcseconds (radius, 90% containment). This
location is 56 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 1.49
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 902 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image processing
FAILED because of no aspect solution. Results from the list of sources
generated on-board are not available at this time. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.19. 

The "B" burst name is based on the Fermi/GBM detection 
circular of this burst (GCN Circ. 26659). 

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/)