//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3961 SUBJECT: GRB050911: Swift-BAT detection of a long burst DATE: 05/09/11 16:30:59 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift K. Page (U. Leicester), M. Chester (PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), J. Kennea (PSU), C. Markwardt (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC), on behalf of the Swift team: At 15:59:34 UT, Swift-BAT triggered and located GRB050911 (trigger=154630). The BAT on-board calculated location is RA,Dec 13.692, -38.861 {00h 54m 46s, -38d 51' 37"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows multi- peaks with short peaks (< 500 msec) at T-1 sec and T+0 sec, and a broader peak between T+10 to T+20 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at the time of the trigger. Due to the Earth limb observing constraint, the spacecraft could not slew immediately. The burst will become visible to the Narrow Field Instruments at 16.52 UT (approximately 51 minutes after the trigger), at which point XRT data will be obtained. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3962 SUBJECT: GRB 050911: z~0.16 cluster in the field DATE: 05/09/11 16:50:31 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Carnegie Observatories) reports: "The position of GRB 050911 is located about 3.5 arcmin from the center of a galaxy cluster (EDCC 493; diameter ~ 20 arcmin). Several galaxies in this field have a redshift of about 0.165, measured in the Las Campanas Redshift Survey (LCRS). If GRB 050911 is a short burst (as may be indicated by the initial short duration pulses; GCN 3961), then it is possible that it is associated with EDCC 493, and is therefore located at z~0.16. We note that the prompt emission exhibits a second peak at t+10 to t+20 sec (GCN 3961), but this may be a softer component as observed in GRBs 050709 and 050724." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3964 SUBJECT: GRB 050911: Swift-BAT refined analysis DATE: 05/09/11 19:24:11 GMT FROM: Takanori Sakamoto at NASA/GSFC J. Tueller (GSFC), L. Barbier (GSFC), S. Barthelmy (GSFC), M. Chester (PSU), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. Marshall (GSFC), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), on behalf of the Swift-BAT team: Using the data set from T-60 to T+120 sec from the recent telemetry downlink, we report further analysis of Swift-BAT GRB 050911 (trigger #154630) (Page, et al., GCN 3961). The refined BAT ground position is (RA,Dec) = 13.718, -38.862 { 0h 54m 52.4s, -38d 51' 42.8"} [deg; J2000] +-2.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 43 %. The mask-weighted BAT light curves show at least three peaks. The first two peaks are at T-1 and T+0 sec, each with a duration of 0.5 sec. The third peak is a slow rise and decay from T+10 to T+20 sec. The third peak is not appreciably softer than the first two, as suggested by Berger (GCN Circ 3962). Thus the burst is very likely in the long GRB category. T90 (15-350 keV) is (16 +- 2) sec. (estimated error including systematics). The power law index of the time-averaged spectrum is 1.87 +- 0.03. The fluence in the 15-150 keV band is (3.0 +- 0.6) x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T0-0.1 sec in the 15-150 keV band is (1.3 +- 0.2) ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3965 SUBJECT: GRB 050911, optical observations DATE: 05/09/11 23:31:57 GMT FROM: Alberto Castro-Tirado at LAEFF-INTA P. Tristram (Univ. of Canterbury, New Zealand), A. J. Castro-Tirado, S. Guziy, A. de Ugarte Postigo, M. Jelinek, J. Gorosabel (IAA-CSIC, Granada, Spain), and Ph. Yock (Univ. of Auckland, New Zealand) report: "We have imaged the GRB 050911 error box provided by Swift/BAT (Page et al. GCN 3961) with the 0.6m telescope (+MOA camera) at Mt. John Observatory. 5 x 300s second integrations in the wide R-band filter were taken starting at 16:35:16 UT (i.e. 36 min after burst). Within the refined Swift/BAT error box (Tueller et al. GCN 3964), the coadded image does not reveal any variable object down to R~21 when comparing to the DSS-2." This message can be quoted. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3966 SUBJECT: GRB 050911: LCO observations DATE: 05/09/12 04:02:04 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Carnegie Observatories) and A. Boss (Carnegie DTM) report: "We observed the BAT error circle of GRB 050911 (GCN #3961) with the du Pont 100-inch telescope at Las Campanas Observatory on 2005, Sep. 12.125 UT (13 hours after the burst). A total of 16 minutes were obtained in I-band with a seeing of about 0.9". A comparison to DSS reveals no new objects to the limit of the survey." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3967 SUBJECT: GRB050911: Swift-XRT position DATE: 05/09/12 07:17:54 GMT FROM: Kim Page at U.of Leicester K. Page (U. Leicester), J. Kennea (PSU) and D. Burrows (PSU) report on behalf of the Swift XRT team: We have analysed the first 3 orbits of ground data from GRB050911 (BAT Trigger 154630). There is a previously uncatalogued X-ray source within the BAT error circle at a position of RA(J2000): 00:54:37.7 Dec(J2000): -38:50:57.7 with an uncertainty of 7.5 arcsec radius (90% containment). This is 107 arcsec from the BAT position reported in GCN 3961 (Page et al.) Because of the limited amount of data, starting only 4.6 hours after the trigger, it is not yet possible to confirm that this source is definitely fading. However, it is the best candidate for the XRT afterglow. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3968 SUBJECT: GRB 050911, optical content of Swift/XRT error box DATE: 05/09/12 08:55:58 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. J. Castro-Tirado, A. de Ugarte Postigo, S. Guziy, M. Jelinek, J. Gorosabel (IAA-CSIC, Granada, Spain), P. Tristram (Univ. of Canterbury, New Zealand) and Ph. Yock (Univ. of Auckland, New Zealand) report: "We have examined the position of the Swift/XRT candidate afterglow for GRB 050911 (Page et al. GCNC 3967) in our 0.6m telescope (+MOA camera) images (Tristram et al. GCNC 3965). In the 7.5" radius X-ray error box, we find three optical sources, which seem to be detected as well in the corresponding DSS-2 red-band plates. Coordinates (J2000) yield: #1 00:54:37.87 -38:51:03.6 #2 00:54:38.10 -38:50:59.7 #3 00:54:38.14 -38:50:56.0 Error= ± 0.5" An ID-chart is posted at: http://www.iaa.es/~deugarte/GRBs/050911/GRB050911.gif Further observations are in progress." This message can be quoted." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3969 SUBJECT: GRB050911: Swift UVOT followup observations DATE: 05/09/12 15:20:35 GMT FROM: Alexander Blustin at MSSL-UCL A. A. Breeveld (UCL-MSSL), K. Page (U. Leicester), T. S. Poole (UCL-MSSL), F. Marshall (GSFC), M. Chester, P. Meszaros, J. Nousek (PSU) on behalf of the Swift/UVOT team: UVOT started observing GRB050911 16408 s (4.56 hours) after the burst (Page et al. GCN 3961). The delay was caused by firstly an earth limb constraint and then Swift spacecraft loss of lock on the star tracker. No new source was found within the XRT error circle (Page et al. GCN 3967) to the following upper limits. Filter T_range (s) Exp (s) 3sig UL V 21591-22041 900 20.2 B 16408-17291 883 21.0 B 28287-28870 583 20.8 U 27380-28280 900 20.9 UVW1 26473-27373 900 21.2 UVM2 22498-23081 583 20.9 UVW2 32261-32961 700 21.4 Where T_range is the time range post-trigger over which the summed images were accumulated and Exp is the total exposure time of the summed image. The magnitude upper limits are not corrected for extinction. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3972 SUBJECT: GRB 050911: LCO limits on a variable source DATE: 05/09/13 02:52:04 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Carnegie Observatories), B. P. Schmidt (RSAA, ANU), A. M. Soderberg (Caltech), and A. Boss (Carnegie DTM) report: "We obtained second set of I-band observations of GRB 050911 with the du Pont telescope at LCO on 2005, Sep. 12.39 UT (18.5 hours after the burst). Digital subtraction of this observation from the one obtained 13 hours after the burst (GCN #3966) reveals no variable sources within the XRT error circle (GCN #3967) to a 3-sigma limit of I>21.9 mag in comparison to the UCAC2 star at RA=00:54:43.4587, DEC=-38:54:00.674." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3976 SUBJECT: GRB050911: Upper limit on X-ray afterglow DATE: 05/09/15 07:13:54 GMT FROM: Kim Page at U.of Leicester K. Page (U. Leicester), D. Burrows (PSU), N. Gehrels (GSFC), P. O'Brien (U. Leicester), F. Marshall (GSFC) and P. Boyd (GSFC-UMBC) report on behalf of the Swift-XRT team: Upon analysis of 29 ks of data, starting 4.6 hours after the BAT detected GRB050911 (trigger number 154630; GCN 3961), no fading X-ray source is found within the BAT refined error circle (GCN 3964; Tueller et al.) The source suggested in GCN 3967 (Page et al.) is found to constant over time, so is not believed to be the afterglow. We place a 3 sigma upper limit of 6.7e-4 count s^-1 on the count-rate, which corresponds to an unabsorbed flux of 2.8e-14 erg cm^-2 s^-1 (over 0.3-10 keV), assuming a Crab-like spectrum. Since this GRB looks like a real burst in the BAT data, we conclude that it must have had a rapidly-decaying X-ray afterglow to have faded below the XRT sensitivity in 4.6 hours.