Gamma-ray Burst 150811

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #18130
  P. Jenke (UAH) reports on behalf of the Fermi GBM Team:
  "At 20:22:13.75 UT on August 11 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150811B (trigger 461017337/150811849). The GBM on-ground location, using the Fermi GBM trigger data, is RA = 188.0, Dec = -13.5 (J2000 degrees, equivalent to 12h 32m 00s, -13d 30'), with an uncertainty of 8.7 degree (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees).
  The angle of the burst direction to the Fermi LAT boresight is 108 degrees.
  The GBM light curve consists of a single peak with a duration (T90) of about 0.6 s (50-300 keV). The time-averaged spectrum from T0-0.13 s to T0+0.64 s is adequately fit by a Band function with Epeak = 1300 +/- 100 keV, Alpha =-0.23 +/- 0.07 and Beta = -3.0 +/- 0.2.
  The event fluence (10-1000 keV) in this time interval is (1.6 +/- 0.1)E-07 erg/cm^2. The 64 ms peak photon flux measured starting from T0-0.13 s in the 10-1000 keV band is 8.6 +/- 0.3 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #18133
  S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks, D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
  K. Hurley, on behalf of the IPN,
  V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa, and A. Goldstein, on behalf of the Fermi GBM team, and
  A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, report:
  The short-duration GRB 150811B has been detected by Fermi (GBM: Jenke, GCN Circ. 18130), Konus-Wind, and INTEGRAL (SPI-ACS), so far, at about 73334 s UT (20:22:14).
  We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:

  ---------------------------------------------
     RA(2000), deg                 Dec(2000), deg
    ---------------------------------------------
    Center:
     186.348 (12h 25m 23s) -14.105 (-14d 06' 20")
    Corners:
     184.572 (12h 18m 17s) -16.337 (-16d 20' 12")
     188.337 (12h 33m 21s) -12.037 (-12d 02' 14")
     187.888 (12h 31m 33s) -11.720 (-11d 43' 10")
     184.110 (12h 16m 26s) -16.010 (-16d 00' 36")
    ---------------------------------------------
  

  The error box area is 3.1 sq. deg, and its maximum dimension is 5.7 deg (the minimum one is 32.5 arcmin). The Sun distance was 52 deg.
  This box may be improved.
  A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB150811_T73329/IPN/
  The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
• GCN Circular #18137
  S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report:
  The short-duration, hard-spectrum, intense GRB 150811B (Fermi GBM detection: Jenke, GCN 18130; IPN triangulation: Golenetskii et al., GCN 18133) triggered Konus-Wind at T0=73329.515 s UT (20:22:09.515).
  The burst light curve shows a single pulse with a duration of ~0.7 s. The emission is seen up to ~10 MeV.
  As observed by Konus-Wind, the burst had a fluence of 9.08(-1.11,+1.22)x10^-6 erg/cm2, and a 16-ms peak energy flux, measured from T0+0.232 s, of 2.89(-0.92,+0.95)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+0.256 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.35(-0.24,+0.29), and Ep = 1197(-220,+299) keV (chi2 = 28/27 dof). Fitting by the GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.51 (chi2 = 28/26 dof).
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150811_T73329/
  All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.