[vsnet-grb-info 17918] GRB 160501A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19365
SUBJECT: GRB 160501A: Swift detection of a burst
DATE:    16/05/01 00:58:55 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

J. R. Cummings (NASA/UMBC), A. P. Beardmore (U Leicester),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. H. Siegel (PSU) and T. N. Ukwatta (LANL) report on behalf of the
Swift Team:

At 00:40:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160501A (trigger=684679).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 286.377, -17.240 which is 
   RA(J2000) = 19h 05m 30s
   Dec(J2000) = -17d 14' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, there
is no clear variation visible in the immediately-available lightcurve
data. 

The XRT began observing the field at 00:42:39.8 UT, 128.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 286.38344,
-17.24088 which is equivalent to:
   RA(J2000)  = 19h 05m 32.03s
   Dec(J2000) = -17d 14' 27.2"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 22 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 (1.62 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.7
(+3.06/-2.65) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.08e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 136 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 upper limit is 19.6 magnitude. 
The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. The typical upper limit is 18.0. 
No correction has been made for the expected extinction corresponding
to E(B-V) of 0.18. 

Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.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.)