GCN Circular 17592

M. H. Siegel (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
A. Y. Lien (GSFC/UMBC), D. Malesani (DARK/NBI),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf
of the Swift Team:

At 04:22:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150317A (trigger=635148).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 138.935, +55.452, which is 
   RA(J2000)  =  09h 15m 45s
   Dec(J2000) = +55d 27' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows three spikes 
spaced about 10 seconds apart, with a total duration of about 35 sec. 
The peak count rate was ~1700 counts/sec (15-350 keV), at ~0 sec 
after the trigger. 

The XRT began observing the field at 04:23:46.5 UT, 64.6 seconds after
the BAT trigger. 
In a 25 s SPER image XRT detects 10 photons at 
RA, DEC 138.9832, 55.4681 which is    
   RA(J2000)  =  09h 15m 55.98s
   Dec(J2000) = +55:28:05.23
with an uncertainty of 8.6 arcsec (radius, 90% containment). This position is 1.9 
arcmin away from the BAT onboard position, within the BAT error circle. 

We notice the presence of a bright star (R~11) at 11 arcseconds from the XRT 
position. At this time we cannot exclude that emission from the star 
may be affecting the XRT data. 

UVOT took a finding chart exposure of 250 seconds with the U filter
starting 126 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 none 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 expected extinction corresponding to E(B-V) of
0.03. 

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.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/too.html.)