Gamma-ray Burst 120916A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #13777
  G. Vianello (SLAC), M. Ohno (Hiroshima U.), and V. Connaughton (UAH) report on behalf of the Fermi-LAT team:
  On Sept. 16, 2012, Fermi LAT detected high energy emission from GRB 120916A, which was also detected by Fermi-GBM (trigger 120916173). Fermi GBM triggered at T0 = 04:08:40 UTC, although emission from the GRB is clearly seen starting at ~T0-60 s. GBM did not trigger on this earlier emission period owing to the triggering being disabled while Fermi was passing through a region of high geomagnetic latitude. The GRB was also detected by the IPN which provided us a preliminary position (private communication, circular to appear).
  The best LAT on-ground location is found to be RA, Dec 205.81, 36.66 (J2000) with an error radius of 0.3 deg (68% containment, statistical error only), this was 29 deg from the LAT boresight at the time of the trigger. This localization has been found using LAT SOURCE data class in a time interval of ~500 seconds around the GRB time.
  The LAT data show a significant increase in counts at energies >100 MeV, starting around T0, i.e., several seconds after the beginning of the low-energy emission. A standard likelihood analysis yields a photon index of -2.0 +/- 0.5 and a flux of (1.6 +/- 1.0) x 10^-9 erg/ cm^2/s (100 MeV - 10 GeV).
  We note that the transient is not significantly detected using LAT TRANSIENT class data, even though the LAT TRANSIENT data appear by eye to follow the lightcurve seen at lower energies in the GBM. This lack of a significant signal in the LAT TRANSIENT data is due to the low signal-to-noise ratio in that class resulting from the high non-photon background corresponding to the high geomagnetic latitude.
  The Fermi LAT point of contact for this burst is Masanori Ohno (ohno@hep01.hepl.hiroshima-u.ac.jp ).
  The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
• GCN Circular #13778
  K. Hurley, and J. Goldsten, on behalf of the MESSENGER GRNS GRB team,
  S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
  A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
  V. Connaughton, M. Briggs, and C. Meegan, on behalf of the Fermi GBM team,
  S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team, and
  K. Yamaoka, M. Ohno, Y. Hanabata, Y. Fukazawa, T. Takahashi, M. Tashiro, Y. Terada, T. Murakami, and K. Makishima on behalf of the Suzaku WAM team, report:
  The long-duration, moderately intense GRB 120916A (Fermi-LAT detection: Vianello, Ohno, and Connaughton, GCN 13777) has been observed by INTEGRAL (SPI-ACS), Konus-Wind, Fermi (GBM: trigger 369461323), MESSENGER (GRNS), Swift (BAT), and Suzaku (WAM), so far, at about 14866 s UT (04:07:46). The burst was outside the coded field of view of the BAT.
  We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:

     ---------------------------------------------
      RA(2000), deg                 Dec(2000), deg
     ---------------------------------------------
     Center:
      205.631 (13h 42m 31s) +36.700 (+36d 42' 00")
     Corners:
      207.209 (13h 48m 50s) +35.578 (+35d 34' 41")
      204.206 (13h 36m 49s) +37.722 (+37d 43' 20")
      203.936 (13h 35m 45s) +37.776 (+37d 46' 33")
      206.960 (13h 47m 50s) +35.646 (+35d 38' 44")
     ---------------------------------------------
  

  The error box area is 0.298 sq. deg, and its maximum dimension is 3.42 deg. This elongated box intersects the LAT error circle
  This box may be improved.
  A triangulation map showing the error box and the LAT error circle is posted at http://www.ioffe.ru/LEA/GRBs/GRB120916_T14864/IPN/
  The time history and spectrum will be given in forthcoming GCN Circulars.
• GCN Circular #13781
  S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report:
  The long-duration GRB 120916A (Fermi-LAT detection: Vianello et al., GCN 13777; IPN detection and localization: Hurley et al., GCN 13778) triggered Konus-Wind at T0=14864.136s UT (04:07:44.136)
  The light curve shows a multi-peaked structure with a total duration of ~30 s followed by a weaker and softer pulse at ~T0+50 s. The emission in the main bursting episode is seen up to 9 MeV.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB120916_T14864/
  As observed by Konus-Wind, the burst had a fluence of 1.7(-0.3,+0.3)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.864 s, of 4.5(-1.5,+1.5)x10-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The time-integrated spectrum (measured from T0 to T0+24.832 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.0 (-0.1, +0.2), the high energy photon index beta = -4.2 (-5.8, +1.6), the peak energy Ep = 335(-90, +65) keV, chi2 = 71.5/90 dof.
  The spectrum at the maximum count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.7 (-0.2, +0.2), the high energy photon index beta = -2.3 (-7.7, +0.2), the peak energy Ep = 320(-70, +120) keV, chi2 = 97.9/86 dof.
  All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.
• GCN Circular #13782
  G. Fitzpatrick (UCD) reports on behalf of the Fermi GBM Team:
  At 04:08:40.75 UT on 16 September 2012, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 120916A (trigger 369461323/120916173) which was also detected by Fermi LAT (G. Vianello et al. GCN 13777), Konus-Wind (S. Golenetskii et al. GCN 13781) and the IPN (K. Hurley et al. GCN 13778).
  The on-ground calculated location is consistent with the LAT location.
  The GBM light curve consists of 3 peaks with a duration (T90) of about 53 s (50-300 keV). The last peak is softer and corresponds to the trigger time, the earlier emission begins at ~T0-60 s. GBM did not trigger on this earlier emission period owing to the triggering being disabled while Fermi was passing through a region of high geomagnetic latitude.
  The time-averaged spectrum from T0-53 s to T0+0.2 s is best fit by a Band function with Epeak = 312.40 (+51.30/-47.20) keV, alpha = -0.99 (+0.06/-0.06), and beta = -1.90 (+0.09/-0.12).
  The event fluence (10-1000 keV) in this time interval is (1.95 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+-30.7205 s in the 10-1000 keV band is 9.72 +/- 0.28 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.
• GCN Circular #13816
  H. Ueno, M. Tashiro, Y. Terada, W. Iwakiri, T. Yasuda, M. Asahina, S. Kobayashi, A. Sakamoto, Y. Ishida, S. Sugimoto (Saitama U.), M. Akiyama, N. Ohmori, M. Yamauchi (Univ. of Miyazaki), K. Yamaoka, Y. E. Nakagawa (Waseda U.), Y. Hanabata, T. Kawano, K. Takaki, R. Nakamura, Y.Tanaka, M. Ohno, Y. Fukazawa (Hiroshima U.), S. Sugita (Nagoya U.), M. Kokubun, T. Takahashi (ISAS/JAXA), Y. Urata, P. Tsai (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo), on behalf of the Suzaku WAM team, report:
  The long GRB 120916A (Fermi-LAT detection: Vianello et al., GCN 13777; IPN detection and localization: Hurley et al., GCN 13778) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 04:07:46.689 UT (=T0).
  The observed light curve shows a multi-peaked main structure starting at T0-2 s, ending at T0+30 s with the total duration (T90) is about 26 seconds. A weaker and softer pulse followed the main component from T0+50 s to T0+60 s. The fluence of main pulse in 100 - 1000 keV was 1.11 (-0.09, +0.13) x 10^-5 erg/cm^2
  The 1-s peak flux measured at T0+23 s was 5.25 (-0.41, +0.46) photons/cm^2/s in the same energy range.
  Preliminary result shows that the time-averaged spectrum from T0-2 s to T0+28 s is well fitted by a power-law with exponential cutoff model:

  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
    alpha : 0.97(-1.01, +0.70)
    Epeak : 342 (-72, +106) keV (chi^2/d.o.f = 5.18/14).
  

  Due to the brightness of this burst, a 3% systematic error was added for low energy channels. All the quoted errors are at statistical 90% confidence level.
  The light curves for this burst will be available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html