Gamma-ray Burst 110820B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #12299
  K. Hurley and J. Goldsten, on behalf of the MESSENGER NS 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,
  S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team,
  D. M. Smith, R. P. Lin, J. McTiernan, R. Schwartz, and W. Hajdas, on behalf of the RHESSI GRB team, report:
  On 2011 August 20 at about 21:27:50 UT, an extremely intense, very long duration GRB was observed by Konus-Wind, MESSENGER, RHESSI, and Swift (BAT) (outside the coded field of view). We have triangulated it to a preliminary, 3 sigma error box whose area is 0.212 sq. deg. and whose coordinates are:

  ------------------------------------------------
        RA(2000), deg              Dec(2000), deg
  ------------------------------------------------
  Center:
     157.583 (10h 30m 20s)   -54.605 (-54d 36' 16")
  Corners:
     159.392 (10h 37m 34s)   -54.329 (-54d 19' 45")
     156.617 (10h 26m 28s)   -54.836 (-54d 50' 09")
     155.769 (10h 23m 05s)   -54.841 (-54d 50' 27")
     158.541 (10h 34m 10s)   -54.362 (-54d 21' 44")
  ------------------------------------------------
  

  Some improvement to this error box is possible. The time history and spectrum will be given in a forthcoming GCN Circular.
• GCN Circular #12301
  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 hard extremely intense GRB 110820B (localized by IPN: Hurley et al., GCN 12299) triggered Konus-Wind at T0=3D77268.054s UT (21:27:48.054)
  The event light curve shows two major bursting episodes separated by ~100 s. A weaker and softer emission is observed at the time between the two main pulses. The total duration of the burst is ~200s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB110820_T77268/
  As observed by Konus-Wind the burst had a fluence of (2.5 =B1 0.3)x10-4 erg/cm2, and a 64-ms peak flux, measured from T0+3.136 s, of (2.6 =B1 0.4)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The time-integrated spectrum of the burst (measured from T0 to T0+191.488 s) is best fitted in the 20 keV - 10 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha =3D -1.22 (-0.05, +0.06), the high energy photon index beta =3D -2.1 (-0.3, +0.2), the peak energy Ep =3D 481(-83, +90) keV, chi2 =3D 69/84 dof.
  The spectrum at the maximum count rate (measured from T0+0.256 to T0+3.840 s) is best fitted in the 20 keV - 10 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha =3D -0.55 (-0.09, +0.09), the high energy photon index beta =3D -2.5 (-0.4, +0.2), the peak energy Ep =3D 483(-53, +60) keV, chi2 =3D 81/84 dof.
  All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.