TITLE: GCN CIRCULAR NUMBER: 19681 SUBJECT: GRB 160709A, Swift-BAT detection and localization DATE: 16/07/11 23:01:33 GMT FROM: Amy Lien at GSFC T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), J. P. Norris (BSU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): At 19:49:03.464 UT on 2016-07-09, BAT detected a count rate increase and a sub-threshold signal in the image. Due to the sub-threshold nature, this event did not trigger a normal burst event-by-event response. Using the data set from T-2 to T+8 sec from the recent telemetry downlink, the ground analysis found an 8.8 sigma detection in a 10-s image in 15-350 keV. As discussed below, this is likely the same burst, GRB160709A, that was detected by Fermi/GBM (Jenke et al. GCN Circ. 19676), Fermi/LAT (Guiriec et al. GCN Circ. 19675), and Konus-Wind (Frederiks et al. GCN Circ. 19677). The BAT ground-calculated position is RA, Dec = 235.996, -28.188 deg which is RA(J2000) = 15h 43m 59.1s Dec(J2000) = -28d 11' 18.2" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 19%. The mask-weighted light curve shows a multi-peaked structure that starts at ~T0 and peaks at ~T+0.8 s. The main pulses end at ~T+1 s, but there are some weak emissions that continue beyond the event data range. T90 (15-350 keV) estimated from the raw light curve is 4.8 +- 1.6 sec (estimated error including systematics). The time-averaged spectrum from T+0.0 to T+4.8 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.11 +- 0.28. The fluence in the 15-150 keV band is 4.5 +- 0.7 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.30 sec in the 15-150 keV band is 2.7 +- 0.4 ph/cm2/sec. All the quoted errors are at the 90% confidence level. Using a 16-ms binned light curve, the lag of the initial pulse (~T0 to ~T+1 s) for the 100-350 keV to 25-50 keV bands is 3 (+/-5) ms (with 1-sigma error). Using a 4-ms binned light curve, the lag of the initial pulse for the same energy bands is 6 (+/-5) ms. These values are consistent with those from a short GRB. The detection time of this burst is only ~0.04 s from the Fermi/GBM trigger time of GRB160709A (Jenke et al., GCN Circ. 19676). Also, the burst structure is very similar to the one seen in the GBM. We thus believe the BAT detection is highly likely to be GRB160709A. However, we note that the BAT location is ~0.33 degrees from the LAT location and outside of the reported LAT error circle of 0.18 deg (statistical error only; Guiriec et al. GCN Circ. 19675). The large dispersion in the position measurements may be explained by the unknown systematic uncertainty in the LAT position. Nonetheless, we cannot rule out the possibility that these are independent events. The BAT location for this burst is covered by the XRT tiling search. No XRT or UVOT afterglows are found within the BAT error circle. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/703769/BA/