TITLE:   GCN CIRCULAR
NUMBER:  17621
SUBJECT: GRB 150323C: Swift detection of a burst
DATE:    15/03/23 17:15:23 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

A. Amaral-Rogers (U Leicester), W. H. Baumgartner (GSFC/UMBC),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 17:05:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150323C (trigger=636005).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 192.613, +50.198 which is 
   RA(J2000) = 12h 50m 27s
   Dec(J2000) = +50d 11' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of at least 40 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 17:08:11.3 UT, 169.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 192.6177, 50.1910 which is equivalent to:
   RA(J2000)  = +12h 50m 28.25s
   Dec(J2000) = +50d 11' 27.6"
with an uncertainty of 5.2 arcseconds (radius, 90% containment). This
location is 27 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 178 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 expected extinction corresponding to E(B-V) of
0.01. 

Burst Advocate for this burst is A. Amaral-Rogers (aar14 AT le.ac.uk). 
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.)