[vsnet-grb-info 17781] GRB 160325A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19222
SUBJECT: GRB 160325A: Swift detection of a burst
DATE:    16/03/25 07:31:21 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

E. Sonbas (Adiyaman Univ.), A. Y. Lien (GSFC/UMBC) and
K. L. Page (U Leicester) report on behalf of the Swift Team:

At 07:00:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160325A (trigger=680436).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 15.597, -72.706 which is 
   RA(J2000) = 01h 02m 23s
   Dec(J2000) = -72d 42' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 80 sec. One of the major pulses occurred 
at ~ -40 s before BAT trigger during spacecraft slews. The peak count rate
was ~9000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 07:01:10.0 UT, 66.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 15.65210,
-72.69671 which is equivalent to:
   RA(J2000)  = 01h 02m 36.50s
   Dec(J2000) = -72d 41' 48.2"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 67 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (5.91 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.3
(+2.60/-2.22) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.15e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 74 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. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
0.00% of the XRT error circle. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com). 
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.)