TITLE: GCN CIRCULAR NUMBER: 16214 SUBJECT: GRB 140506A: Swift detection of a burst with an optical counterpart DATE: 14/05/06 21:28:16 GMT FROM: David Burrows at PSU/Swift B.P. Gompertz (U Leicester), D. N. Burrows (PSU), S. B. Cenko (GSFC), S. T. Holland (Eureka), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (NASA/GSFC/ORAU), V. Mangano (PSU), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 21:07:36 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140506A (trigger=598284). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 276.790, -55.562 which is RA(J2000) = 18h 27m 10s Dec(J2000) = -55d 33' 43" 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 ~6500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 21:09:14.7 UT, 97.9 seconds after the BAT trigger. XRT found a bright, fading, uncatalogued X-ray source located at RA, Dec 276.7752, -55.6353 which is equivalent to: RA(J2000) = +18h 27m 6.05s Dec(J2000) = -55d 38' 07.1" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 265 arcseconds from the BAT onboard position. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.01e-08 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 320 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 18:27:06.03 = 276.77513 DEC(J2000) = -55:38:08.8 = -55.63577 with a 90%-confidence error radius of about 0.63 arc sec. This position is 1.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.46 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.09. Burst Advocate for this burst is B.P. Gompertz (bpg6 AT le.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/too.html.)