//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12373 SUBJECT: GRB 110921A: Swift detection of a burst DATE: 11/09/21 14:01:54 GMT FROM: David Burrows at PSU/Swift W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), P. A. Evans (U Leicester), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), O. M. Littlejohns (U Leicester), V. Mangano (INAF-IASFPA), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), P. T. O'Brien (U Leicester), C. Pagani (U Leicester), K. L. Page (U Leicester), J. L. Racusin (NASA/GSFC), T. Sakamoto (NASA/UMBC), B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU), E. Sonbas (GSFC/USRA/Adiyaman Univ.), R. L. C. Starling (U Leicester) and B.-B. Zhang (PSU) report on behalf of the Swift Team: At 13:51:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110921A (trigger=503652). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 294.078, +36.377 which is RA(J2000) = 19h 36m 19s Dec(J2000) = +36d 22' 36" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a ragged, single-peaked structure with a duration of about 10 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 13:53:22.5 UT, 122.4 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 294.09838, 36.32882 which is equivalent to: RA(J2000) = 19h 36m 23.61s Dec(J2000) = +36d 19' 43.8" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 182 arcseconds from the BAT onboard position, outside the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.43 x 10^21 cm^-2, Kalberla et al. 2005), with an excess column of 3.1 (+2.28/-1.97) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 125 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.14. Burst Advocate for this burst is W. H. Baumgartner (wayne AT milkyway.gsfc.nasa.gov). 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.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12374 SUBJECT: GRB 110921A: MASTER-Net early limit DATE: 11/09/21 15:00:27 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.Yurkov, Yu.Sergienko, E.Sinyakov, D.Varda, I.Kudelina Blagoveschensk Educational State University, Blagoveschensk K.Ivanov, S.Yazev, N.M.Budnev, E.Konstantinov, V.Lenok, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, N.Tyurina, N.Shatskiy, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov, D.Zimnukhov, M. Kornilov, A.Sankovich Sternberg Astronomical Institute, Moscow State University A. Tlatov, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov Ural State University, Kourovka MASTER II robotic telescopes (MASTER-Net: http://observ.pereplet.ru) located in Amur and in Tunka (Siberia) was pointed to the GRB110921A 7 sec after notice time and 53 sec after GRB time at 2011-09-21 13:52:13.432 UT. On our first (10s exposure) set we haven`t found optical transient within SWIFT error-box (ra=19 36 19 dec=+36 22 48 r=0.050000). Observations were made in polarizing bands. The 5-sigma upper limit has been about 17.2 in Amur and 17.5 in Tunka. Observations and data reduction is continued. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12377 SUBJECT: GRB 110921A : TNT optical counterpart candidate DATE: 11/09/21 16:30:38 GMT FROM: L.P. Xin at NAOC L.P. Xin, J.Y. Wei, Y. L. Qiu, J. Wang, J.S. Deng, C. Wu, X. H. Han on behalf of EAFON report: We began to observe GRB 110921A (Baumgartner et al., GCN 12373) with Xinglong TNT telescope at 13:59:40 (UT), about 8 min after the burst. 25 White-band images and a series of R-band data were obtained. A new source was detected in the combined white band image within the errorbox of XRT position. The brightness of this new source is estimated to be about 20.2 mag derived from USNO B1.0 R2mag. We propose that this source is the candidate of optical counterpart of GRB 110921A. More deep observations are needed to confirm this. This message may be cited. For more information about Xinglong GRBs Follow-up observations, please visit the website: http://www.xinglong-naoc.org:8080/grb/index.html //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12378 SUBJECT: GRB 110921A: MITSuME Akeno Optical Observation DATE: 11/09/21 16:38:54 GMT FROM: Yoichi Yatsu at Tokyo Tech. K. Tokoyoda, M. Hayashi, Y. Yatsu, Y. Aoki, K. Kawakami, S. Song, R. Usui, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed GRB 110921A (W. H. Baumgartner et al, GCN12373) with the optical three color (g, Rc, and Ic) CCD camera attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The follow-up observation was started at 13:53:08, ~108 sec after the BAT trigger. We did not find optical counterpart in g'-band and R-band within the enhanced XRT error circle (W. H. Baumgartner et al, GCN12373). While, in I-band, we detected a very faint OT candidate in the error circle only in the earliest data-set (T0+108s ~ T0 + 348s). Further data analysis for the I-band data is now ongoing. Photometric results are listed below. We used GSC2.3 catalog for flux calibration. T0+[s] MID-UT T-EXP[sec] g' Rc Ic --------------------------------------------------------------------------------- +108 14:07:40 1530 >20.0 >19.5 --- --------------------------------------------------------------------------------- T0+ : Elapsed time after the burst [sec] T-EXP: Total Exposure time [sec] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12379 SUBJECT: GRB 110921A: Enhanced Swift-XRT position DATE: 11/09/21 20:01:29 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1830 s of XRT Photon Counting mode data and 3 UVOT images for GRB 110921A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 294.09821, +36.32864 which is equivalent to: RA (J2000): 19h 36m 23.57s Dec (J2000): +36d 19' 43.1" with an uncertainty of 1.9 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12380 SUBJECT: GRB 110921A: optical observations in Mt. Terskol and Maidanak observatories DATE: 11/09/21 20:40:56 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Pozanenko (IKI), M. Andreev, A. Sergeev (Terskol Branch of Institute of Astronomy), M. Ibrahimov (MAO) on behalf of larger GRB follow up collaboration report: We observed the field of the Swift GRB 110921A (Baumgartner et al., GCN 12373) with Zeiss-600 telescope of Mt. Terskol observatory and AZT-22 telescope of Maidanak observatory on Sep. 21. Several images were taken in both observatories in R filter. Within the enhanced XRT error box (Goad et al., GCN 12379) we do not detect the candidate of optical counterpart of GRB 110921A (Xin et al., GCN 12377). Preliminary photometry of a combined image (Zeiss-600) and a single image of AZT-22 is based on the nearby USNO B1.0 stars: UT Filter, Exposure, OT, Upper Limit (3 sigma) Telescope (mid) (s) Sep.21 16:50 R 1800 n/d 21.1 Zeiss-600 Sep.21 17:48 R 300 n/d 21.2 AZT-22 Since our photometry is somewhat deeper than photometry of the candidate (Xin et al., GCN 12377), we could suggest the candidate is a real afterglow of GRB 110921A. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12383 SUBJECT: GRB 110921A, Swift-BAT refined analysis DATE: 11/09/22 01:08:38 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 110921A (trigger #503652) (Baumgartner, et al., GCN Circ. 12373). The BAT ground-calculated position is RA, Dec = 294.094, 36.355 deg which is RA(J2000) = 19h 36m 22.6s Dec(J2000) = +36d 21' 19.8" with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 15%. The mask-weighted light curve shows multiple weak peaks. T90 (15-350 keV) was 48.00 +- 22.63 sec (estimated error including systematics). The time-averaged spectrum from T-31.55 to T+16.45 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.57 +- 0.17. The fluence in the 15-150 keV band is 2.4 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+7.95 sec in the 15-150 keV band is 0.2 +- 0.4 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/503652/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12384 SUBJECT: GRB 110921A: Swift-XRT refined Analysis DATE: 11/09/22 08:05:33 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) and W. H. Baumgartner (GSFC/UMBC) report on behalf of the Swift-XRT team: We have analysed 9.7 ks of XRT data for GRB 110921A (Baumgartner et al. GCN Circ. 12373), from 134 s to 40.9 ks after the BAT trigger. The data comprise 47 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN. Circ 12379). The light curve can be modelled with a power-law decay with a decay index of alpha=0.90 (+/-0.05). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.00 (+0.15, -0.14). The best-fitting absorption column is 2.0 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 1.4 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.0 (+0.5, -0.4) x 10^21 cm^-2 Galactic foreground: 1.4 x 10^21 cm^-2 Excess significance: 7.9 sigma Photon index: 2.00 (+0.15, -0.14) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00503652. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12385 SUBJECT: GRB 110921A: TNT astrometry DATE: 11/09/22 10:16:28 GMT FROM: Dong Xu at Weizmann Inst D. Xu (WIS), L.P. Xin, J.Y. Wei (NAOC) report on behalf of a larger collaboration: We performed astrometry to the TNT image (Xin et al., GCN 12377), calibrated with the SDSS field of GRB 110921A (Baumgartner et al., GCN 12373). The optical afterglow is localised at RA (J2000): 19h 36m 23.478s Dec (J2000): +36d 19' 43.38" with an uncertainty of 1.0 arcsec, in the northwestern part of the enhanced XRT error circle (Goad et al., GCN 12379). The SDSS field reveals a source at coordinates RA (J2000): 19h 36m 23.382s Dec (J2000): +36d 19' 42.03" with an uncertainty of 1.0 arcsec and at the southwestern edge of the XRT error circle, which is too faint to be present for the TNT image. NIR follow-up observation is encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12386 SUBJECT: GRB 110921A: Fermi GBM observation DATE: 11/09/22 15:47:15 GMT FROM: Gerard Fitzpatrick at UCD G. Fitzpatrick (UCD) reports on behalf of the Fermi GBM Team: "At 13:51:22.57 UT on 21 September 2011, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 110921A (trigger 338305884 / 110921577), which was detected by the Swift/BAT (Baumgartner et al. 2011, GCN 12373). The GBM on-ground location is consistent with the Swift position. The GBM light curve shows a single bright peak with a duration (T90) of ~37 s (50-300 keV). The time-averaged spectrum from T0-26 s to T0+9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.39 +/- 0.12 and the cutoff energy, parameterized as Epeak, is 139 +/- 32 keV. The event fluence (10-1000 keV) in this time interval is (4.2 +/- 0.4)E-06 erg/cm^2. The 1 s peak photon flux measured starting from T0+0.5 s in the 10-1000 keV band is 2.9 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12387 SUBJECT: GRB 110921A: NOT observations DATE: 11/09/22 16:11:30 GMT FROM: Paul Vreeswijk at U of Iceland Paul Vreeswijk (U. Iceland), Daniele Malesani, Antonio de Ugarte Postigo (DARK, NBI), Dong Xu (WIS), Páll Jakobsson, Steve Schulze (U. Iceland) and Nial Tanvir (U. Leicester) report on behalf of a larger collaboration: Using ALFOSC on the Nordic Optical Telescope (NOT) we have obtained Sloan r'- (3 x 600 s) and z'-band (6 x 300 s) imaging of the field of GRB 110921A (Baumgartner et al., GCN 12373, Barthelmy et al., GCN 12383), starting on 2011 September 21.925 UT (roughly 8.3 hr after the burst). The observations were performed through clouds, but under good seeing conditions (~0.8"). We do not detect the optical afterglow reported by Xin et al. (GCN 12377, see also Xu et al., GCN 12385), or any other object within the enhanced Swift-XRT error circle (Goad et al., GCN 12379), down to limiting magnitudes of about r'=23.3 and z'=21.0 (calibrated against the SDSS catalog). Just outside the enhanced XRT error circle, at R.A.(J2000) 19:36:23.38, decl.(J2000) 36:19:42.1 (with an uncertainty of 0.23"), we detect an r'=22.4+-0.2 source, also visible - albeit barely - in the combined z'-band imaging. This apparent point source is consistent, both in position and brightness, with the SDSS object noted by Xu et al. (GCN 12385). We are grateful for the NOT staff, particularly Fatemeh Sadat Kiaeerad and Marjaana Lindborg, for obtaining these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12389 SUBJECT: GRB 110921A: Swift/UVOT Observations DATE: 11/09/23 14:23:26 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (MSSL-UCL) and W. H. Baumgartner (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 110921A 126 s after the BAT trigger (Baumgartner et al., GCN Circ. 12373). A source consistent with the optical position (Xin et al., GCN Circ. 12377 and Xu et al., GCN Circ. 12385) is detected at 3.5 sigma in the summed white data, but is not seen in any of the other filters, nor in any of the white exposures individually. Preliminary magnitudes and 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 126 276 147 >21.3 u_FC 284 534 246 >20.6 white 126 1704 411 21.4 ± 0.3 v 614 5307 308 >20.3 b 540 1679 117 >20.7 u 284 1654 343 >20.9 w1 664 1629 117 >21.1 m2 639 1604 117 >19.7 w2 590 1725 132 >20.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.14 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12410 SUBJECT: GRB 110921A: MITSuME-Akeno Optical photometry DATE: 11/09/30 16:46:34 GMT FROM: Yoichi Yatsu at Tokyo Tech. K. Tokoyoda, M. Hayashi, Y. Yatsu, Y. Aoki, K. Kawakami, S. Song, R. Usui, and N. Kawai (Tokyo Tech)  report on behalf of the MITSuME collaboration: As reported in GCN12378 (Tokoyoda et al.), we detected a very faint object within the XRT error circle of GRB 110921A (W. H. Baumgartner et al, GCN12373) with the MITSuME-Akeno 50cm telescope. Here we report the results of aperture photometry. We started the follow-up observation at 13:53:08 (UT), ~108 sec after the BAT trigger(W. H. Baumgartner et al, GCN12373). The optical counterpart can be seen both in R and I band only in the earliest data-set from T0+108s to T0 + 348s. For zero-point calibration we used GSC2.3 catalog. The g' magnitudes of the reference stars were estimated based on Sesar et al. (2006). For I-band data we could not find any usable catalog data, therefore we performed a field photometry. The Photometric results are summarized below. Filter  T0+[s]  MID-UT  T-EXP[sec]   Mag  Mag_err   LimitMag ----------------------------------------------------------------------------------- g'        +108    13:55:31        240        ---      ---           >19.4 Rc      +108    13:55:31        240       18.8    0.2           --- Ic        +108    13:55:13        210       18.8    0.3           --- ----------------------------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12438 SUBJECT: GRB 110921A: optical observations DATE: 11/10/16 01:25:38 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (SAI MSU), A. Pozanenko (IKI), E. Klunko (ISTP), V. Rumyantsev (CrAO), N.Pit (CrAO) on behalf of larger GRB follow up collaboration report: We observed the field of the Swift GRB 110921A (Baumgartner et al., GCN 12373) with AZT-33IK telescope of Sayan observatory (Mondy) on Sep. 21 between (UT) 14:36:31 -- 16:05:00 and AZT-11 telescope of CrAO on Sep. 21 between (UT) 17:38:46 -- 19:00:15. In a combined image of a few first frames taken with AZT-33IK we detected a faint source which coincides with the optical counterpart of GRB 110921A (Xin et al., GCN 12377; Xu et al., GCN 12385). A photometry is based on the star USNO B1.0 1263-0338839 (19 36 21.52 +36 19 56.2) assuming R=16.13 T0+, Filter, Exposure, OT, UL(3 sigma), Telescope (mid, d) (s) 0.03934 R 850 22.08 +/- 0.18 22.3 AZT-33IK 0.07558 R 1920 n/d 22.5 AZT-33IK 0.18620 R 4860 n/d 21.3 AZT-11 In a combined image of a total exposure of 3030 s taken with AZT-33IK telescope we clearly detected the SDSS object noted by Xu et al. (GCN 12385) and Vreeswijk et al. (GCN 12387). The photometry of the SDSS object against the above calibration star is R=22.8 +/- 0.3. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12617 SUBJECT: GRB 110921A: optical observations in Maidanak observatory DATE: 11/12/04 20:50:27 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (SAI MSU), M. Ibrahimov (UBAI), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We update results of Maidanak observations preliminary reported in GCN 12380. We observed the field of the Swift GRB 110921A (Baumgartner et al., GCN 12373) with AZT-22 telescope of Maidanak observatory starting Sep. 21 (UT) 17:45:30. Several images in R-filter of 300 s exposure were taken under moderate seeing (FWHM ~ 1.7"). We detect a source in coordinates (J2000) 19 36 23.363 +36 19 43.02 with uncertainty of 0.2" and brightness of R = 22.0 +/- 0.15. This source is rather consistent both in position and brightness, with the SDSS object (Xu et al. GCN 12385; Vreeswijk et al. GCN 12387). So we do not detect afterglow reported by (Xu et al. GCN 12385; Breeveld et al. GCN 12389; Tokoyoda et al. GCN 12410; Volnova et al. GCN 12438). Tstart UT, T0+, Filter, Exposure, OT, Upper Limit (3 sigma) (mid, d) (s) 17:45:30 0.17895 R 8*300 n/d 22.5