TITLE:   GCN CIRCULAR
NUMBER:  27536
SUBJECT: GRB 200411A: Swift detection of a short burst
DATE:    20/04/11 04:43:03 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

A. Tohuvavohu (U Toronto), S. D. Barthelmy (GSFC), J. A. Kennea (PSU),
N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and
T. N. Ukwatta (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 04:29:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200411A (trigger=965784).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 47.659, -52.314, which is 
   RA(J2000)  =  03h 10m 38s
   Dec(J2000) = -52d 18' 51"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 0.5 sec.  The peak count rate
was ~6000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:29:53.0 UT, 50.7 seconds after
the BAT trigger. The position determined from promptly downlinked data
differs significantly from the on-board position, suggesting that the
XRT may have centroided on a cosmic ray; the initial XRT position
notice should be treated with caution. Using promptly downlinked data
we find a fading, uncatalogued X-ray source located at RA, Dec
47.66239, -52.31805 which is equivalent to:
   RA(J2000)  = 03h 10m 38.97s
   Dec(J2000) = -52d 19' 05.0"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 16 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 (1.55 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.4
(+5.14/-3.83) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 58 seconds after the BAT trigger. Further analysis is
required before any results can be obtained. 

Burst Advocate for this burst is A. Tohuvavohu (tohuvavohu AT astro.utoronto.ca). 
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/)