TITLE:   GCN CIRCULAR
NUMBER:  36938
SUBJECT: GRB 240727A: Swift detection of a burst
DATE:    24/07/27 04:06:04 GMT
FROM:    David Palmer at LANL <palmer@lanl.gov>


T. M. Parsotan (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL)
and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels
Swift Observatory Team:

Prior to 03:48 UTC, BAT triggered and located GRB 240727A
(Trigger 1245074) and slewed to the GRB location. 
Due to a telemetry gap, no further BAT information
will be available until the next data downlink to the ground. 

The XRT began observing the field at 03:48:12 UT. Using promptly downlinked data 
we find a bright, uncatalogued X-ray source located at RA, Dec 236.43742, 8.62001 
which is equivalent to:
   RA(J2000)  = 15h 45m 44.98s
   Dec(J2000) = +08d 37' 12.0"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). 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 (3.64 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.7
(+3.19/-2.66) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 2.08e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting at 03:48:20. Automatic processing FAILED due to its reliance
on BAT data for initial parameters. 

Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov). 
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/)