This file contains both the GRB 070920 'A' and 'B' bursts. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6805 SUBJECT: GRB 070920: Swift detection of a burst DATE: 07/09/20 04:19:07 GMT FROM: David Palmer at LANL D. Grupe (PSU), N. Gehrels (NASA/GSFC), F. E. Marshall (NASA/GSFC), C. Pagani (PSU), D. M. Palmer (LANL), J. L. Racusin (PSU), G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU), M. C. Stroh (PSU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the Swift Team: At 04:00:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070920 (trigger=291614). The BAT on-board calculated location is RA, Dec 100.932, +72.227 which is RA(J2000) = 06h 43m 44s Dec(J2000) = +72d 13' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is often the case with 64-second image triggers, the BAT light curve shows no obvious variation in the count rate. Because Swift is in the process of returning to normal operations, automatic slewing to GRBs is currently disabled. Therefore, there are no prompt XRT or UVOT observations of this burst. Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.edu). 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: 6806 SUBJECT: GRB 070920: TAROT Calern observatory optical observations DATE: 07/09/20 05:04:31 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report: We imaged the field of GRB 070920 detected by SWIFT (trigger 291614) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France. The observations started 544.7s after the GRB trigger (6.8s after the notice). The elevation of the field increased from from 57 degrees above horizon and weather conditions were excellents. The date of trigger : t0 = 2007-09-20T04:00:14.112 The first image is 90.0s exposure in tracking mode: t0+544.7s to t0+634.7s : R > 18.2 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. N.B. Galactic coordinates are lon=142.6283 lat=+25.1560 and the galactic extinction in R band is 0.3 magnitudes estimated from D. Schlegel et al. 1998ApJ...500..525S. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6807 SUBJECT: GRB 070920, Swift-BAT refined analysis DATE: 07/09/20 15:29:46 GMT FROM: Scott Barthelmy at NASA/GSFC L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Grupe (PSU), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-119 to T+300 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070920 (trigger #291614) (Grupe, et al., GCN Circ. 6805). The BAT ground-calculated position is RA, Dec = 100.968, 72.250 deg which is RA(J2000) = 06h 43m 52.2s Dec(J2000) = 72d 14' 59" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted lightcurve shows a single peak (with structure) starting at ~T-15 sec, broadly peaking at ~T+25 sec, and ending at ~T+140 sec. T90 (15-350 keV) is 56 +- 1 sec (estimated error including systematics). The time-averaged spectrum from T+15.1 to T+75.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.69 +- 0.21. The fluence in the 15-150 keV band is 5.1 +- 0.7 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+30.45 sec in the 15-150 keV band is 0.3 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6808 SUBJECT: GRB 070920B: Swift detection of a burst DATE: 07/09/20 21:13:46 GMT FROM: Scott Barthelmy at NASA/GSFC J. L. Racusin (PSU), S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/GSFC/USRA), H. A. Krimm (GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), C. Pagani (PSU), D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the Swift Team: At 21:04:32 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070920B (trigger=291728). The BAT on-board calculated location is RA, Dec 0.144, -34.819 which is RA(J2000) = 00h 00m 35s Dec(J2000) = -34d 49' 06" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 35 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. Because Swift is in the process of returning to normal operations, automatic slewing to GRBs is currently disabled. Therefore, there are no prompt XRT or UVOT observations of this burst. Burst Advocate for this burst is J. L. Racusin (racusin AT astro.psu.edu). 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: 6809 SUBJECT: GRB 070920B: NOT optical observations DATE: 07/09/21 10:54:32 GMT FROM: Antonio Deugarte at IAA-CSIC A. de Ugarte Postigo, J. Gorosabel, M. Jelinek, A.J. Castro-Tirado (IAA-CSIC, Granada), D. Perez-Ramirez (U. Jaen), R. Corradi (ING, La Palma), T. Liimets (ING, La Palma and Tartuu Obs.) report: We have observed the field of GRB070920B (Racusin et al., GCNC 6808) using the 2.5m NOT telescope (+ALFOSC) at Roque de los Muchachos Observatory in V, R and I bands (180 s each) at high airmass. The mean time of the observations was 21.0486 Sep. 2007 (UT), ~4.1 hours after the burst. We do not detect any bright afterglow candidate within the Swift/BAT error box. However, we do see a red, stationary object (detected in R and I bands) slightly over the DSS2 limit that does not seem to have its correspondent in the DSS2 images. The coordinates of this object are (J2000 +/- 0.5"): R.A.: 00:00:34.56 Dec.: -34:49:08.4 Further observations are needed to confirm wether this could be the optical afterglow of GRB 070920B. A finding chart comparing with the DSS2 can be found at: www.iaa.es/~deugarte/GRBs/070920B/GRB070920B.jpg This message can be quoted. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6811 SUBJECT: GRB 070920B, Swift-BAT refined analysis DATE: 07/09/21 13:22:10 GMT FROM: Scott Barthelmy at NASA/GSFC S.D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), J.L. Racusin (PSU), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070920B (trigger #291728) (Racusin, et al., GCN Circ. 6808). The BAT ground-calculated position is RA, Dec = 0.127, -34.844 deg which is RA(J2000) = 00h 0m 30.5s Dec(J2000) = -34d 50' 39" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted lightcurve shows a symmetrical peak starting at ~T-20 sec, peaking at ~T+1 sec, and ending at ~T+17 sec. T90 (15-350 keV) is 20.2 +- 0.2 sec (estimated error including systematics). The time-averaged spectrum from T-11.2 to T+13.4 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.67 +- 0.58, and Epeak of 41.3 +- 4.5 keV (chi squared 45.21 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 6.6 +- 0.5 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T-0.49 sec in the 15-150 keV band is 0.8 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.00 +- 0.10 (chi squared 67.16 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. [GCN OPS NOTE(21sep07): Per author's request, the 'B' was added to the GRB name in the first sentence.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6812 SUBJECT: GRB 070920b: LCO optical observations DATE: 07/09/21 13:40:32 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Princeton,OCIW) and W. Krzeminski (LCO) report: "We observed the BAT error circle of GRB 070920b (GCN 6808) with the Swope 40-inch telescope at Las Campanas Observatory starting on 2007 Sep. 21.22 UT (8.2 hours after the burst). A total of 30 minutes were obtained in R-band in mediocre seeing conditions (~1.5"). A comparison to DSS reveals no new objects within the revised BAT error circle (GCN 6811)." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6814 SUBJECT: GRB 070920b, SMARTS optical observation DATE: 07/09/21 18:11:29 GMT FROM: Bethany Cobb at Yale U B. E. Cobb, part of the larger SMARTS consortium, reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical imaging of the error region of GRB 070920b (Racusin et al. GCN 6808) with a mid-exposure time of ~4.4 hours post-burst (2007-09-21 01:29 UT). The total summed exposure time amounted to 36 minutes in I, but images were taken under poor weather conditions. Comparison to the DSS reveals no new sources in the refined GRB error region (Barthelmy et al. GCN 6811). Our I-band limiting magnitude is I~20.8 (calibrated using several USNO-B1.0 stars). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6816 SUBJECT: GRB 070920B: TAROT La Silla observatory optical observations DATE: 07/09/22 06:09:32 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report: We imaged the field of GRB 070920B detected by SWIFT (trigger 291728) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 2.7h after the GRB trigger (beginning of the night). The elevation of the field increased from from 27 degrees above horizon and weather conditions were good but the moon (phase=0.58) was only at 68 degrees of the field, limiting the detectivity. We co-added a series of 8 x 180s unfiltered exposures. We do not detect any OT in the refined position provided by Barthelmy et al. (GCNC 6811) nor the source reported by de Ugarte Postigo et al. (GCNC 6809): t0+2.7h to t0+3.6h : R > 18.2 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction (which is very low along the line of sight). This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6820 SUBJECT: GRB 070920B: XRT observations DATE: 07/09/23 21:13:45 GMT FROM: Judith Racusin at PSU J. L. Racusin (PSU) reports on behalf of the Swift-XRT team: We have analysed 9.7 ks of Swift XRT data for GRB 070920B (Racusin et al., GCN 6808) beginning 64 ks after the BAT trigger. The data are entirely in Photon Counting mode, and reveal a faint uncatalogued X-ray source at RA, Dec= 0.13029, -34.85284 degrees, which is equivalent to: RA (J2000) = 00h 00m 31.27s Dec(J2000) = -34d 51' 10.2" with an estimated uncertainty of 8.0 arcsec (radius, 90% containment including boresight uncertainty). This is 33 arcsec from the refined BAT position (Barthelmy et al. GCN 6811). The source has a count rate of 2.1e-3 +/- 0.6e-3 counts s-1. At present we are unable to determine whether the source is fading, however observations are ongoing. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6824 SUBJECT: GRB 070920B: ROTSE-III Early Optical Limits DATE: 07/09/25 19:11:20 GMT FROM: Heather Swan at U.of Michigan/ROTSE H. Swan (U Mich), E.S. Rykoff (UCSB), F. Yuan (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 070920B (Swift trigger 291728; J. L. Racusin, GCN 6808), producing images beginning 8.5 s after the GCN notice time. An automated response took the first image at 21:05:16.5 UT, 44.1 s after the burst, under partly cloudy conditions. We took 10 5-sec, 10 20-sec and 386 60-sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). We lost internet contact with ROTSE-IIIc shortly after the GCN trigger, thus we were unable to retrieve the burst data until Sept. 25. Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle or the XRT error circle , (J. L. Racusin, GCN 6820) for both single images and coadding into sets of 10; the field is not crowded. Individual images have limiting magnitudes ranging from 12.8-17.8; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 21:05:16.5 21:05:21.5 5 15.7 44.1 N 21:05:16.5 21:06:34.5 78 16.7 44.1 Y 21:29:06.7 21:34:44.6 337 17.8 1474.3 Y //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6854 SUBJECT: GRB070920A: MAGIC telescope GeV observation DATE: 07/10/06 08:21:21 GMT FROM: Nicola Galante at MPI,Muenchen Galante N. (MPI/Muenchen), Garczarczyk M. (MPI/Muenchen), Gaug M. (IAC/Tenerife), Bastieri D. (U. Padova), Longo F. (INFN/Trieste) and Scapin V. (U. Udine), for the MAGIC Collaboration The MAGIC Imaging Atmospheric Cherenkov Telescope performed a follow-up observation of the SWIFT/BAT burst GRB070920A (GCN circular 6805, Grupe D., et al.). We received the GCN alert at T0+539s. The data taking by MAGIC started at T0+690s, 2.5 minutes after the alert income. We observed the sky positon for 36min spanning a zenith angle in the range 53-50 degrees. No evidence for VHE gamma-ray emission above the analysis threshold of about 250 GeV was found. A preliminary analysis, taking advantage for the first time of the fast 2GHz digitalization from the new data acquisition system, and for the hypothesis of steady emission and assumption of a differential photon spectral index of -2.5, yields the following 95% CL differential flux upper limits (inc. 30% systematic error on the efficiency): E(225-300 GeV) : 7.1 x 10^(-8) erg/cm^2 E(300-400 GeV) : 4.6 x 10^(-8) erg/cm^2 E(400-1000 GeV) : 2.2 x 10^(-8) erg/cm^2 E(1-10 TeV) : 0.53 x 10^(-8) erg/cm^2 The upper limits correspond to the time period between T0+690s and T0+2490s. We can also exclude emission of a constant flux during our observation in any 100s time bin higher than: E(225-300 GeV) : 1.9 x 10^(-7) erg/cm^2 E(300-400 GeV) : 1.0 x 10^(-7) erg/cm^2 E(400-1000 GeV) : 2.4 x 10^(-8) erg/cm^2 This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6921 SUBJECT: GRB 070920A: deep optical observations at the NOT DATE: 07/10/16 11:32:48 GMT FROM: Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center A.O. Jaunsen (Univ. Oslo), J. Gorosabel (IAA-CSIC), J.P.U. Fynbo, D. Malesani, J. Sollerman, Ch. Gall (DARK), T. Morel (Leuven), M.D. Stritzinger (DARK), A. Somero, J. Telting, C. Villforth (NOT), report on behalf of a larger collaboration: We observed the field of GRB 070920A (Grupe et al., GCN #6805) in the R band with the Nordic Optical Telescope on 2007 September 20.209-20.221 UT (1.0-1.3 hr after the GRB). Comparison images were taken on September 20.216 and again on October 15.135 UT with the same telescope, instrumentation and filter. Our images cover 96% of the revised BAT error circle(Barbier et al., GCN #6807), missing a small region at the northern boundary. At a mean time of 1.15 hr after the GRB, we do not detect any variable object brighter than R=24.3 (calibrated against USNO-B1.0, R1 magnitudes). There is no evidence for an associated SN on Oct. 15 down to the same limit.