TITLE: GCN CIRCULAR NUMBER: 17376 SUBJECT: GRB 150202A: Swift detection of a burst DATE: 15/02/02 23:36:34 GMT FROM: Scott Barthelmy at NASA/GSFC H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), M. M. Chester (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and T. N. Ukwatta (LANL) report on behalf of the Swift Team: At 23:10:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150202A (trigger=629547). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 39.236, -33.150, which is RA(J2000) = 02h 36m 57s Dec(J2000) = -33d 08' 59" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve show several peaks swith a total duration of about 30 sec. The peak count rate was ~1600 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 23:11:30.3 UT, 88.0 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 39.2275, -33.1485 which is equivalent to: RA(J2000) = 02h 36m 54.61s Dec(J2000) = -33d 08' 54.5" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 26 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (2.54 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.3 (+1.96/-1.74) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 304 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. Data from the list of sources generated on-board are not available at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. Burst Advocate for this burst is H. A. Krimm (hans.krimm 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.)