TITLE: GCN CIRCULAR NUMBER: 16249 SUBJECT: GRB 140512A: Swift detection of a burst with an optical counterpart DATE: 14/05/12 19:56:20 GMT FROM: Scott Barthelmy at NASA/GSFC C. Pagani (U Leicester), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), V. Mangano (PSU), C. J. Mountford (U Leicester), K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), C. A. Swenson (PSU) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 19:31:49 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140512A (trigger=598819). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 289.371, -15.100 which is RA(J2000) = 19h 17m 29s Dec(J2000) = -15d 05' 59" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a multi-peak event with a total duration of about 170 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~122 sec after the trigger. The XRT began observing the field at 19:33:27.5 UT, 98.4 seconds after the BAT trigger. The position determined from promptly downlinked data differs significantly from the on-board position, suggesting that the XRT may have centroided on a cosmic ray; the initial XRT position notice should be treated with caution. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 289.36925, -15.09492 which is equivalent to: RA(J2000) = 19h 17m 28.62s Dec(J2000) = -15d 05' 41.7" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 19 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. No spectrum from the promptly downlinked event data is yet available to determine the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 106 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 19:17:28.78 = 289.36991 DEC(J2000) = -15:05:39.2 = -15.09423 with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.01 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.16. Burst Advocate for this burst is C. Pagani (cp232 AT star.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.)