Gamma-ray Burst 070911

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #6777
  H. A. Krimm (GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team:
  At 05:57:44 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070911 (trigger=290624). Swift automatic slews are currently disabled, as we are currently recovering from a safehold. The BAT on-board calculated location is RA, Dec 25.799, -33.473 which is

     RA(J2000) = 01h 43m 12s
     Dec(J2000) = -33d 28' 21"
  

  with an uncertainty of 4 arcmin (radius, 90% containment, including systematic uncertainty, however there is an uncalibrated boresight shift due to operations with a different set of gyros than we have used previously). The BAT light curve showed a complex multi-peaked structure with a duration of about 150 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~36 sec after the trigger.
  Because we are in the process of resuming normal operations, there is no automatic follow-up observation by the XRT and UVOT.
  Burst Advocate for this burst is H. A. Krimm (krimm 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.)
• GCN Circular #6778
  D. Palmer (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), A. Parsons (GSFC), 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-299 to T+303 sec from the recent telemetry downlink, we report further analysis of BAT GRB (trigger #290624) (Krimm, et al., GCN Circ. 6777). The BAT ground-calculated position is RA, Dec = 25.819, -33.484 deg which is

      RA(J2000) = 1h 43m 16.5s
      Dec(J2000) = -33d 29' 3"
  

  with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 88%.
  The mask tagged light curve starts to rise at around T-70 sec and continues above baseline until T+160 sec. The burst contains multiple strong peaks in a cluster from T-5 to T+55 sec, then a drop in flux and another cluster of peaks from T+85 to T+145 sec.The first cluster of peaks has a harder spectrum than the second. T90 (15-350 keV) is 162 +- 10 sec (estimated error including systematics).
  The time-averaged spectrum from -73.0 to +158.8 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.04. The fluence in the 15-150 keV band is 1.2 +- 0.02 x 10^-05 erg/cm2. The 1-sec peak photon flux measured from T+36.13 sec in the 15-150 keV band is 3.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
• GCN Circular #6779
  Giulia Stratta (ASDC), Matteo Perri (ASDC) and David Burrows (PSU) report, on behalf of the Swift XRT team:
  We have analyzed the first 9 orbits of Swift-XRT data on GRB 070911 (GCN 6777, Krimm et al.) for a total of 6.8 ks of exposure taken in Photon Counting mode starting 14.5 hours after the burst. This is the first BAT GRB after Swift safe-hold recovery. Swift-XRT detected an uncatalogued, fading source at the following coordinates RA,Dec 25.8094,-33.4842 which is

    RA(J2000)  = 01h 43m 14.26s
    Dec(J2000) = -33d 29' 03.1"
  

  with an estimated error radius of 6 arcseconds (90% confidence). This error radius has been increased to take into account the uncertainties in the pointing calibration during Swift's reactivation phase. This position is 0.5' from the BAT refined position (GCN 6778, Palmer et al.). We note however that XRT position uncertanties are currently being re-validated.
  The 0.3-10 keV X-ray light curve from T0+14.5 h to T0+27.3 h can be fit with a simple power law model. The best fit decay index is alpha=-1.5+/-0.2
  The 0.3-10.0 keV X-ray spectrum with 6.8 ks of integration time, is well fit by an absorbed power law with a photon index of 2.2 +/- 0.3 and a total column density of NH=(1.3+/-0.5)e21 cm**-2 (chi2/dof=0.8/6). The Galactic column density in the direction of the source is 2.4e20 cm**-2 (Dickey & Lockmann 1990). The 0.3-10 keV observed flux is 1.9e-12 erg cm**-2 s**-1 (unabsorbed: 2.8e-12 erg cm**-2 s**-1). We note that the XRT CCD is now operating with a raised substrate voltage, and thus has a different gain. The new gain is not yet well calibrated, and so our spectral results are only preliminary.
  Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV count rates of 0.02 cts/s 2 days after the burst trigger, that corresponds to a flux of 1.3e-12 erg cm**-2 s**-1.
  This is an official product of the Swift XRT team.
• GCN Circular #6780
  N. Butler, D. Starr, J. S. Bloom (UCB) report:
  In simultaneous J, H, and Ks band observations of the GRB 070911 field (Krimm et al.; GCN 6777) starting on September 11 08h53m33s UT, 2 hrs, 56 min after the burst, we find no new sources in the XRT error region (Stratta et al.; GCN 6779). We derive the following limiting magnitudes: J > 16.5 mag, H > 16 mag, and Ks > 16 mag.
  This message may be cited.
• GCN Report 82.1
  GCN_Report 82.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_82_1.pdf by H.A. Krimm at CRESST/USRA/GSFC titled: "Swift Observations of 070911"
• GCN Circular #6790
  Y. E. Nakagawa, K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. Terada, T. Tamagawa (RIKEN), M. Ohno, T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.), M. Tashiro, Y. Urata, A. Endo, K. Onda, M. Suzuki, N. Kodaka, K. Morigami (Saitama U.), T. Enoto, R. Miyawaki, K. Nakawaza, K. Makishima (Univ. of Tokyo), E. Sonoda, M.Yamauchi, S. Maeno, H. Tanaka, R. Hara (Univ. of Miyazaki), M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA), S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report:
  The long GRB 070911 (Swift/BAT trigger #290624 ; Krimm et al., GCN 6777; Palmer et al., GCN 6778) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 2007-09-11 05:58:20 UT (=T0).
  The observed light curve shows a multi-peaked structure lasting from T0-160s to T0+120s, with a duration (T90) of about 182 seconds. The fluence in 100 - 2000 keV was 1.4 (+0.3, -0.3) * 10^-5 erg/cm^2. The 1-s peak flux measured from T0+0s was 1.1 (+0.3, -0.2) photons/cm^2/s in the same energy range.
  Preliminary result shows that the time-averaged spectrum from T0-160s to T0+120s is well fitted by a single power-law with a photon index of 1.9 (+0.3, -0.4) (chi^2/d.o.f = 8.7/16).
  All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included.
  The light curves for this burst are available at:
  http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
• GCN Circular #6810
  L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) on behalf of the Swift-BAT team,
  M. Ohno, T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.), Y. E. Nakagawa, K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. Terada, T. Tamagawa (RIKEN), K. Morigami, N. Kodaka, K. Onda, M. Tashiro, M. Suzuki, Y. Urata, A. Endo (Saitama U.), T. Enoto, R. Miyawaki, K. Nakawaza, K. Makishima (Univ. of Tokyo), E. Sonoda, M. Yamauchi, S. Maeno, H. Tanaka, R. Hara (Univ. of Miyazaki), M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA), S. Hong (Nihon U.), on behalf of the Suzaku-WAM team,
  report:
  We performed the Swift/BAT, and Suzaku/WAM joint fit spectral analysis of GRB 070911 (Swift-BAT trigger #290624; Krimm, et al., GCN Circ. 6777). The time interval of the spectral data for each instrument is chosen from T0(WAM)-56 to T0(WAM)+149 sec where T0(WAM) is the trigger time of WAM at 05:58:20.069 UTC. The energy ranges which we used in the joint spectral analysis are 14-150 keV and 100-1000 keV for Swift/BAT and Suzaku/WAM respectively. The spectral data of two instruments are fit with the spectral model multiplied by the constant factor to take into account the systematic uncertainties in the response matrices of each instrument.
  The spectrum is well fit with a power-law with exponential cutoff model (dN/dE ~ E^{alpha} * exp(-(2+alpha)*E/Epeak)). The constant factors of each instrument agree within 10%. No systematic residual from the best fit model is seen in the spectral data of each instrument. The best fit spectral parameters are: alpha = -1.6 +- 0.1 and Epeak = 170 (-50/+280) keV (chi2/dof = 59/74). The energy fluence in the 15-1000 keV band calculated by a power-law with exponential cutoff model for this 205 sec interval is 2.1 (-0.2/+0.4) x 10^-5 erg/cm2 (assuming the constant factor of the BAT is fixed to 1).
  All the quoted errors are at the 90% confidence level.
• GCN Circular #6829
  B. E. Cobb, part of the larger SMARTS consortium, reports:
  Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 070911 (Krimm et al. GCN 6777) with the following mid-exposure times:

           2007-09-13 07:10:30 UT -  2.05 days post-burst
           2007-09-15 06:42:00 UT -  4.03 days post-burst
           2007-09-22 05:22:21 UT - 10.98 days post-burst
  

  For each observation, total summed exposure times amounted to 36 minutes in I and 30 minutes in J.
  A fading afterglow is detected in both I and J within the X-ray afterglow error region (Stratta et al. 6779). This afterglow has the following coordinates and magnitudes:
  RA/DEC: 01:43:14.4 -33:29:02.5

  days post
  burst           I-magnitude (or limit)  J-magnitude (or limit)
  ----------------------------------------------------------------
    2.05           20.9 +/- 0.1            19.8 +/- 0.2
    4.03           21.9 +/- 0.2           >19.5 +/- 0.1
   10.98          >22.3 +/- 0.1           >19.7 +/- 0.1
  

  The I-band photometry is calibrated to a number of secondary stars in the field of GRB 070911. The magnitude of these secondary stars was derived using Landolt standard star observations obtained during the first two epochs, which were photometric night at CTIO. The J-band images are calibrated based on several 2MASS stars in the field.
  The afterglow's behavior between the first two epochs is consistent with a decay rate of alpha = -1.4+/-0.3. Interestingly, no J-band afterglow was detected by Butler et al. (GCN 6780) to J > 16.5 only 3 hours after the burst. This indicates that a period of rebrightening might have occurred between 3 hours and 2 days post-burst, though steady decay is only ruled out at the ~1 sigma level.
• GCN Report 82.2
  GCN_Report 82.2 has been posted: http://gcn.gsfc.nasa.gov/reports/report_82_2.pdf by H.A. Krimm at CRESST/NASA/GSFC/USRA titled: "Final Swift Observations of GRB 070911"