[vsnet-grb-info 20169] GRB 171222A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22265
SUBJECT: GRB 171222A: Swift detection of a burst
DATE:    17/12/22 16:42:04 GMT
FROM:    Judith Racusin at GSFC  <judith.racusin at nasa.gov>

J. L. Racusin (NASA/GSFC), A. Deich (PSU), S. W. K Emery (UCL-MSSL),
J.D. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (NSF/USRA),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
B. Sbarufatti (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Swift Team:

At 16:24:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171222A (trigger=799669).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 148.293, +35.622 which is 
   RA(J2000) = 09h 53m 10s
   Dec(J2000) = +35d 37' 18"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the BAT light 
curve does not show any significant features. 

The XRT began observing the field at 16:27:49.5 UT, 169.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 148.27784, 35.62759 which
is equivalent to:
   RA(J2000)  = 09h 53m 06.68s
   Dec(J2000) = +35d 37' 39.3"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 48 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. 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 6.69e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
175 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 19.2 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 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.01. 

Burst Advocate for this burst is J. L. Racusin (judith.racusin 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.)