TITLE: GCN CIRCULAR NUMBER: 43089 SUBJECT: GRB 251214B: Swift detection of a burst with an optical counterpart DATE: 25/12/14 09:28:08 GMT FROM: K.L. Page at U Leicester klp5@leicester.ac.uk

R. A. J. Eyles-Ferris (U Leicester), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. M. Parsotan (GSFC) report on behalf of the Neil Gehrels Swift Observatory Team:

At 09:02:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251214B (trigger=1423875). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 330.217, -9.167 which is RA(J2000) = 22h 00m 52s Dec(J2000) = -09d 10' 00" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 10 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 09:03:18.2 UT, 60.7 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 330.21095, -9.16335 which is equivalent to: RA(J2000) = 22h 00m 50.63s Dec(J2000) = -09d 09' 48.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 25 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 https://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 (4.01 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.2 (+2.80/-2.44) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter starting 63 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 22:00:50.52 = 330.21052 DEC(J2000) = -09:09:46.7 = -9.16296 with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.47. No correction has been made for the expected extinction corresponding to E(B-V) of 0.039.

Burst Advocate for this burst is R. A. J. Eyles-Ferris (raje1 AT leicester.ac.uk). 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/)

View this GCN Circular online at https://gcn.nasa.gov/circulars/43089. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...