GCN Circular 20538

C. B. Markwardt (NASA/GSFC), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), A. Cholden-Brown (PSU), A. D'Ai (INAF-IASFPA),
V. D'Elia (ASDC), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 14:21:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170127A (trigger=735326).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 174.336, -45.852, which is 
   RA(J2000)  =  11h 37m 21s
   Dec(J2000) = -45d 51' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a couple weak peaks
with a duration of about 35 sec.  The peak count rate
was ~900 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 14:22:51.5 UT, 95.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 174.35974, -45.83603 which
is equivalent to:
   RA(J2000)  = 11h 37m 26.34s
   Dec(J2000) = -45d 50' 09.7"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 82 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 http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 7.10e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
101 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
0.07. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt 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/too.html.)