TITLE:   GCN CIRCULAR
NUMBER:  28263
SUBJECT: GRB 200819A: Swift detection of a burst
DATE:    20/08/19 16:04:22 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

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

At 15:43:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200819A (trigger=992099).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 21.428, +63.048 which is 
   RA(J2000) = 01h 25m 43s
   Dec(J2000) = +63d 02' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 10 sec.  The peak count rate
was ~1600 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 15:45:17.4 UT, 84.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 21.4240, 63.0614 which
is equivalent to:
   RA(J2000)  = 01h 25m 41.76s
   Dec(J2000) = +63d 03' 40.9"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 48 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 9.84
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 88 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 19.6 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 mag. No
correction has been made for the large, but uncertain, extinction expected. 

We note that this source is near the Galactic plane (lat=0.45, lon=126.8 
degrees) which raises the possibility that this is a new Galactic transient. 
The source is somewhat soft (visible above 50 keV but not above 100 keV). 
The lightcurve is consistent with either a GRB or a Galactic transient. 
The complete dataset from this event and further observations of
the source will determine the nature of this source. 
If it is a Galactic transient we would name it Swift J0125.7+6303 . 

Burst Advocate for this burst is S. Dichiara (dichiara AT umd.edu). 
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/)