TITLE: GCN CIRCULAR NUMBER: 17874 SUBJECT: GRB 150527A: Swift detection of a burst DATE: 15/05/27 07:03:59 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U Leicester), S. D. Barthelmy (GSFC), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and T. N. Ukwatta (LANL) report on behalf of the Swift Team: At 06:48:55 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150527A (trigger=641698). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 288.958, +4.194 which is RA(J2000) = 19h 15m 50s Dec(J2000) = +04d 11' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 40 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 06:49:57.6 UT, 61.8 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 288.9599, 4.2013 which is equivalent to: RA(J2000) = 19h 15m 50.39s Dec(J2000) = +04d 12' 04.7" with an uncertainty of 2.3 arcseconds (radius, 90% containment). This location is 27 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.67 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 67 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain extinction expected. Burst Advocate for this burst is P. A. Evans (pae9 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.)