TITLE: GCN CIRCULAR NUMBER: 21995 SUBJECT: GRB 171010B: Swift detection of a burst DATE: 17/10/11 19:18:11 GMT FROM: Amy Lien at GSFC D. M. Palmer (LANL) and A. Y. Lien (GSFC/UMBC), report on behalf of the Swift team: At 20:59:24.168 UT on 2017-10-10, the Swift Burst Alert Telescope (BAT) triggered on GRB 171010B (trigger=778019). However, on-board analysis was truncated by a pre-planned slew to a scheduled target. Subsequent ground analysis using data from T+1 to T+11 s finds the source at a location of RA, Dec = 34.123, -54.410 deg which is RA(J2000) = 02h 16m 29.6s Dec(J2000) = -54d -24' -36.7" with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 71%. The BAT light curve shows a single-peaked structure that starts and peaks at ~T0, and ends at ~ T+30 s. Because the burst was not identified on board, the event data available (~T+1 to ~T+11) do not cover the entire burst duration. T90 estimated from the BAT raw light curve (15-350 keV) is about 30.4 s. The time-averaged spectrum from T+1.0 to T+11.1 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.41 +- 0.18. The fluence in the 15-150 keV band is 3.9 +- 0.5 x 10^-7 erg/cm2. All the quoted errors are at the 90% confidence level. This event was also detected by Fermi/GBM (trigger 529361971). A Swift Target of Opportunity observation has been requested. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/778019/BA/