TITLE: GCN CIRCULAR NUMBER: 11842 SUBJECT: GRB 110328A / Swift J164449.3+573451: BAT refined analysis DATE: 11/03/30 17:06:00 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), A. Melandri (INAF-OAB), D. M. Palmer (LANL), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) The source originally identified as GRB 110328A (Cummings et al. GCN Circ. #11823 and Barthelmy et al. GCN Circ. #11824) has triggered BAT several times. It is a highly unusual object. It is coincident with an optical source at redshift z = 0.35 (Levan et al., GCN Circ #11833), as well as a radio source (Zauderer et al., GCN Circ #11836). The source continues to be detectable and variable in BAT more than 40 hours after the initial trigger, with peak brightness on the order of 200 mCrab. The source is at high galactic latitude, 39.4 degrees. The summary of BAT triggers so far is: TrigNum Date Time TrigDur Intensity UT [sec] [c/sec] 450158 28 Mar 12:57:45 1208 6.1 450161 28 Mar 13:40:41 64 19.4 450257 29 Mar 18:26:25 320 15.6 450258 29 Mar 19:57:45 64 38.2 This table does not represent all the possible triggers, because the on- board triggering algorithm requires the intensity of the any following event to be slightly more than twice the previous intensity. Also note that the on-board threshold was commanded to zero between the 2nd and 3rd triggers in order to enhance future triggers, and that it was later commanded to be 4 times the 4th trigger's intensity after the 4th trigger to suppress further triggers. The observation of the source including the discovery image was T-4 sec to T+1211 sec. A fit to a power law spectrum from BAT survey data on this interval has a photon index of 1.72 ± 0.18. The fluence from 15 to 150 keV using this model was (3.0 ± 0.3) x 10^-6 ergs/cm^2. The first followup observation, during which the second trigger occurred, was T+1465 sec to T+2348 sec. The photon index from that observation was 1.37 ± 0.11. The fluence was (2.7 ± 0.2) x 10^-6 ergs/cm^2. The light curve from the BAT transient monitor (15-50 keV): http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/SwiftJ164449.3p573451/ shows variability, but that the source was first detectable on 25-March-2011 and has, on average, continued to brighten since the trigger. Please see also Kennea et al., ATel#3242 for more information: http://www.astronomerstelegram.org/?read=3242