A. Tohuvavohu (PSU), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. D'Avanzo (INAF-OAB), A. Deich (PSU),
S. W. K Emery (UCL-MSSL), P. A. Evans (U Leicester), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:
At 11:57:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171212A (trigger=796778). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 293.900, +20.568 which is
RA(J2000) = 19h 35m 36s
Dec(J2000) = +20d 34' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a complex
structure with a duration of about 120 sec. The peak count rate
was ~800 counts/sec (15-350 keV), at ~90 sec after the trigger.
The XRT began observing the field at 11:58:52.7 UT, 91.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 293.91826,
20.59159 which is equivalent to:
RA(J2000) = 19h 35m 40.38s
Dec(J2000) = +20d 35' 29.7"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 104 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
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.23
x 10^22 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 1.28e-08 erg cm^-2 s^-1 (0.2-10
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 99 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.
Because this event is very close to the Galactic plane (lat=0.03 degrees)
it is possibly a Galactic transient, in which case it takes the
name 'Swift J1935.7+2036'.
Burst Advocate for this burst is A. Tohuvavohu (aaronb AT swift.psu.edu).
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.)