GCN Circular 13243
Subject
GRB 120422A: Swift detection of a burst
Date
2012-04-22T07:22:49Z (12 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
E. Troja (NASA/GSFC/ORAU), V. D'Elia (ASDC), C. Guidorzi (U Ferrara),
E. A. Hoversten (PSU), H. A. Krimm (CRESST/GSFC/USRA),
A. Y. Lien (NASA/GSFC/ORAU), O. M. Littlejohns (U Leicester),
A. Melandri (INAF-OAB), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Swift Team:
At 07:12:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120422A (trigger=520658). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 136.929, +14.006 which is
RA(J2000) = 09h 07m 43s
Dec(J2000) = +14d 00' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single complex peak
structure with a duration of about 10 sec. The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 07:13:38.7 UT, 95.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 136.91183, 14.01873 which
is equivalent to:
RA(J2000) = 09h 07m 38.84s
Dec(J2000) = +14d 01' 07.4"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 75 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. We
cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 3.71
x 10^20 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 3.12e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 104 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
0.03.
Burst Advocate for this burst is E. Troja (eleonora.troja AT 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.)