TITLE: GCN CIRCULAR NUMBER: 17413 SUBJECT: GRB 150206A: Swift detection of a burst with an optical afterglow DATE: 15/02/06 15:05:06 GMT FROM: Scott Barthelmy at NASA/GSFC L. M. Z. Hagen (PSU), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), M.E. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 14:30:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150206A (trigger=630019). Swift did not immediately slew due to observing constraint. The BAT on-board calculated location is RA, Dec 10.088, -63.182, which is RA(J2000) = 00h 40m 21s Dec(J2000) = -63d 10' 53" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a weak beginning with a strong increase starting at ~T+70 sec. The duration is about 150 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~97 sec after the trigger. The XRT began observing the field at 14:37:57.3 UT, 474.5 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 10.0774, -63.1852 which is equivalent to: RA(J2000) = +00h 40m 18.58s Dec(J2000) = -63d 11' 06.7" with an uncertainty of 5.1 arcseconds (radius, 90% containment). This location is 20 arcseconds from the BAT onboard position, within the BAT error circle. 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 2.35e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 94 seconds with the White filter starting 483 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:40:17.66 = 10.07358 DEC(J2000) = -63:10:55.6 = -63.18211 with a 90%-confidence error radius of about 0.78 arc sec. This position is 12.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.62 with a 1-sigma error of about 0.16. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. Burst Advocate for this burst is L. M. Z. Hagen (lea.zernow.hagen AT gmail.com). 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.)