Gamma-ray Burst 091120

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #10187
  David Gruber (MPE) reports on behalf of the Fermi GBM Team:
  "At 04:34:40.23 UT on 20 November 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 091120 (trigger 280384482 / 091120191).
  The on-ground calculated location, using the GBM trigger data, is RA = 224.8, DEC = -24.8 (J2000 degrees, equivalent to 14h 59m, -24d 48'), with an uncertainty of 1.32 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees).
  The angle from the Fermi LAT boresight is 45 degrees. Moreover, this burst was bright enough to result in a Fermi spacecraft repointing maneuver.
  The GBM light curve consists of several peaks with a duration (T90) of about 52 s (8-1000 keV). The time-averaged spectrum from T0-3 s to T0+56 s is adequately fit by a power law function with an exponential high energy cutoff. The power law index is -1.17 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 129 +/- 3 keV. (C-stat 691 for 362 d.o.f.).
  The event fluence (8-1000 keV) in this time interval is (3.02 +/- 0.04)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+26.6 s in the 8-1000 keV band is 21.3 +/- 0.4 ph/s/cm^2.
  A Band function fits the spectrum equally well (C-stat 687 for 361 d.o.f.) with Epeak= 124 +/- 4 keV, alpha = -1.15 +/- 0.02 and beta = -2.98 +/- 0.27.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #10188
  M.Nakajima (Nihon U.), S.Nakahira (AGU), M.Sugizaki, M.Kohama(RIKEN), M.Suzuki (ISAS/JAXA), A.Yoshida, K.Yamaoka (AGU), N.Kawai, M.Morii(Tokyo Tech), H.Negoro (Nihon U.), M.Matsuoka, H.Tomida, S.Ueno(ISAS/JAXA), Y.Ueda, S.Eguchi (Kyoto U.) and H.Tsunemi (Osaka Univ.) on behalf of the MAXI team report:
  The Gas Slit Camera (GSC) of MAXI detected a bright hard X-ray transient at 04:34:56 on 20 November 2009 (UT). This event should correspond to a GRB detected by Fermi-GBM, INTEGRAL SPI-ACS andKonus-Wind.
  The location of the source derived from the GSC data is (R.A.,Dec.)=(226.81 deg, -21.79 deg)=(15:07:14.40, -21:47:24.0)(J2000) with an uncertainty of about 0.5 degree. This is consistent with that reported by Gruber (GCNC10187) within an error.
  The GSC FOV scanned over the source from 04:34:56 (UT) (16 seconds after the GBM trigger) for about 40 seconds. The average X-ray flux over the observation is 4.9x10^-8 erg/cm2/s in 3-15 keV. Significant intensity variation was clearly seen in the light curve.
  MAXI is currently under the commissioning phase and the systematic uncertainty in localization will be significantly improved with the progress of the alignment calibration. This message may be citable.
• GCN Circular #10189
  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 GRB 091120 reported by Fermi GBM, (Gruber, GCN 10187) and localized by MAXI GSC (Nakajima et al., GCN 10188) triggered Konus-Wind at T0=16476.183 s UT (04:34:36.183).
  The burst light curve consists of several peaks with a total duration of ~55 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB091120_T16476/ Considerable hard to soft spectral evolution is noticed during the initial part of the burst.
  As observed by Konus-Wind the burst had a fluence of 2.6(+/-0.3)x10-5 erg/cm2, and a 256-ms peak flux measured from T0 + 25.344s of 2.4(+/-0.3)x10-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range).
  The time-integrated spectrum of the burst (from T0 to T0+57.600 s) is well fitted in the 20 keV - 2 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with alpha = -1.2(-0.25, +0.28), and Ep = 145(-18, +26) keV (chi2 = 67/61 dof).
  The spectrum of the most intense peak (measured from T0+24.832 to T0+33.024 s) is also well fitted in the 20 keV - 2 MeV range by a power law with exponential cutoff model, for which alpha = -1.0(-0.4, +0.45), and Ep = 101(-15, +16) keV (chi2 = 48/61 dof).
  All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.
• GCN Circular #10190
  K. Hurley and T. Cline, on behalf of the Mars Odyssey and Konus GRB teams,
  I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,
  W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team,
  S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, and D. Frederiks, on behalf of the Konus-Wind team,
  V. Connaughton, M. Briggs, and C. Meegan, on behalf of the Fermi-GBM team,
  A. von Kienlin, G. Lichti, and A. Rau, on behalf of the INTEGRAL SPI-ACS GRB team,
  D. M. Smith, R. P. Lin, J. McTiernan, R. Schwartz, C. Wigger, and W. Hajdas, on behalf of the RHESSI GRB team, and
  G. Di Cocco, F. Fuschino, M. Galli, C. Labanti, and M. Marisaldi, on behalf of the AGILE MCAL team, report:
  AGILE (MiniCalorimeter), INTEGRAL (SPI-ACS), Konus-Wind, and Mars Odyssey (HEND) observed GRB091120 (Gruber et al. GCN 10187; Nakajima et al. GCN 10188; Golenetskii et al. GCN 10189). We have triangulated this burst to an error ellipse which may be approximated by the following preliminary, 3 sigma error box:

  -----------------------------------------------
      RA(2000), deg              Dec(2000), deg
  -----------------------------------------------
  Center:
    227.393 (15h 09m 34s)   -19.849 (-19d 50' 56")
  Corners:
    226.629 (15h 06m 31s)   -22.609 (-22d 36' 33")
    226.458 (15h 05m 50s)   -22.135 (-22d 08' 05")
    228.539 (15h 14m 09s)   -15.899 (-15d 53' 57")
    228.535 (15h 14m 08s)   -16.885 (-16d 53' 08")
  -----------------------------------------------
  

  The IPN-only error box area is approximately 6600 square arcminutes, and is consistent with the MAXI error circle; the IPN/MAXI error box area is approximately 1000 square arcminutes. This triangulation can be improved.
  A figure showing the GBM, MAXI, and IPN localizations is posted at ssl.berkeley.edu/ipn3/091120