GCN Circular 22930
Subject
GRB 180709A: Swift detection of a burst
Date
2018-07-09T11:11:25Z (6 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), P. A. Evans (U Leicester),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC)
and K. L. Page (U Leicester) report on behalf of the Neil Gehrels
Swift Observatory Team:
At 10:52:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180709A (trigger=846868). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 38.119, +60.372 which is
RA(J2000) = 02h 32m 29s
Dec(J2000) = +60d 22' 18"
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 30 sec. The peak count rate
was ~800 counts/sec (15-350 keV), at ~6 sec after the trigger.
The XRT began observing the field at 10:53:45.0 UT, 104.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
38.1178, 60.3490 which is equivalent to:
RA(J2000) = 02h 32m 28.27s
Dec(J2000) = +60d 20' 56.5"
with an uncertainty of 2.1 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. 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 6.60e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 114 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 large, but uncertain, extinction expected.
Burst Advocate for this burst is F. E. Marshall (marshall 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.)