Gamma-ray Burst 150906B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #18258
  K. Hurley, on behalf of the IPN,
  I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,
  S. Golenetskii, R. Aptekar, 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,
  A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, and
  W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team, report:
  The short-duration, intense GRB 150906B has been detected by Konus-Wind, INTEGRAL (SPI-ACS), Mars-Odyssey (HEND), and Swift (BAT), so far, at about 31345 s UT (08:42:25). 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:
     159.239 (10h 36m 57s) -25.603 (-25d 36' 09")
    Corners:
     158.968 (10h 35m 52s) -25.638 (-25d 38' 17")
     159.102 (10h 36m 24s) -25.740 (-25d 44' 23")
     159.510 (10h 38m 02s) -25.566 (-25d 33' 57")
     159.376 (10h 37m 30s) -25.465 (-25d 27' 54")
    ---------------------------------------------
  

  The error box area is 210 sq. arcmin, and its maximum dimension is 30 arcmin (the minimum one is 8.6 arcmin). The Sun distance was 32 deg.
  This box may be improved.
  A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB150906_T31340/IPN/
  The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
• GCN Circular #18259
  S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A.Kozlova, and T. Cline on behalf of the Konus-Wind team, report:
  The short-duration, hard-spectrum GRB 150906B (IPN triangulation: Hurley, et al., GCN 18258) triggered Konus-Wind at 31340.560 s UT (08:42:20.560).
  The KW light curve shows a single, multi-peaked pulse with a duration of ~2 s. The emission is visible up to ~10 MeV.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150906_T31340/
  As observed by Konus-Wind, the burst had a fluence of 2.8(-0.2,+0.2)x10^-5 erg/cm2, and a 16-ms peak flux, measured from T0+1.488 s, of 2.9(-0.3,+0.3)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The time-averaged spectrum (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by the cutoff power law with the following model parameters: the photon index alpha = -0.43(-0.11,+0.12), and the peak energy Ep = 928(-95,+111) keV, chi2 = 93/94 dof. Fitting this spectrum with the GRB (Band) function yields the same alpha and Ep with an upper limit on beta of -2.8
  All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
• GCN Circular #18263
  A. J. Levan (U. Warwick), N. R. Tanvir (U. Leicester) and J. Hjorth (DARK/NBI) report:
  We note that the preliminary IPN localisation of the short, intense GRB 150906B (Hurley et al. GCN 18258, Golenetskii et al. GCN 18259) lies close to the local galaxy NGC 3313 (z=0.0124, d=54 Mpc). At its closest the IPN error box passes approximately 8.5 arc minutes from the centre of the galaxy, which has a major diameter of 4 arc minutes. This offset corresponds to approximately 130 kpc in projection at 54 Mpc, and is within the range that either kicked neutron star binaries or globular clusters associated with NGC 3313 may be found. In fact, NGC 3313 is the brightest galaxy of a moderate group, and there are several other fainter group members (presumably with shallower potential wells and hence greater typical binary neutron star kick offsets) that lie comparably close to the IPN error region, which are thus also candidate hosts. An image showing the IPN region and group members is at http://www.star.le.ac.uk/~nrt3/NGC3313_group.png .
  At 54 Mpc the inferred isotropic energy of GRB 150906B would be E_iso ~ 10^49 erg, within the range of energetics of known short-GRBs.
  Although it is certainly plausible that the proximity of GRB 150906B to NGC 3313 is a chance alignment, it is of particular interest given that NGC 3313 lies well within the expected detection horizon of Advanced-LIGO/VIRGO for compact binary mergers. Unfortunately the sky location of GRB 150906B means that it is very poorly placed for optical/IR observations at this time.
• GCN Circular #18296
  R. Ruffini, C.L. Bianco, M. Enderli, M. Kovacevic, L. Li, M. Muccino, R. Moradi, G.B. Pisani, J.A. Rueda, Y. Wang report:
  In the GCN 18263 (Levan et al. 2015), the galaxy NGC 3313 (z=0.0124, d=54 Mpc), which lies within the detection horizon of Advanced-LIGO/VIRGO, is presumed to be the host galaxy of GRB 150906B. Consequently, the isotropic energy of GRB 150906B is inferred Eiso~10^{49} erg. In the GCN 18259 (Golenetskii et al., 2015) from Konus-Wind, the time-averaged spectrum of GRB 150906B fitted by a cutoff power law gives the peak energy Ep = 928(-95,+111) keV in the observer's frame.
  From previous GRB statistics (see attached figure [1] and ref. [2]), a typical short GRB with Ep~1 MeV corresponds to Eiso~10^{51} erg. With a fluence of 2.8(-0.2,+0.2)x10^{-5} erg/cm2 from GCN 18259, the redshift of GRB 150906B is expected to be z > 0.06 (266 Mpc), most probably z~0.12 (555 Mpc). Therefore the host galaxy of GRB 150906B could be one of the others nearby.
  This type of short GRBs with Eiso < 10^{52} erg originate from merging neutron stars (NSs) leading to a massive NS and not to a black hole [3]. In view of the small value of the energetic, we indicate these sources as short gamma-ray flash (SGRF). As opposed to the more energetic short gamma-ray bursts, the SGRFs never have GeV emission.

   [1] The MuRuWaZha Ep-Eiso relation: <http://www.icranet.org/documents/MuRuWaZha.pdf>
   [2] Zhang, F.-W., Shao, L., Yan, J.-Z., et al. 2012, ApJ 750, 88
   [3] Ruffini, R., Muccino, M., Kovacevic., et al. 2015 ApJ 808, 190
  

• GCN Circular #18298
  Fu-Wen Zhang (UNLV/GULT), Binbin Zhang (UAH) and Bing Zhang (UNLV) report: GRB 150906B was observed by Konus-Wind as a typical short, bright and spectrally hard burst with Ep=928(-95,+111) keV (Golenetskii et al. GCN 18259). It was suggested (Levan et al. GCN 18263) that it may be associated with NGC 3313 (z=0.0124, d=54 Mpc) with an offset = 130 kpc. Using the flux/fluence and spectral information of Golenetskii et al. GCN 18259, we plot GRB 150906B in the E_p-Eiso (Fig1) and E_p-Liso (Fig 2) diagrams and compare it with other short and long GRBs. We found that GRB 150906B would be a significant outlier of both relations if it had occurred at redshift = 0.01. So if the burst is indeed within the aLIGO horizon, it must be very different from most short GRBs we observe. If one believes this burst is a typical GRB, then it would have a redshift in the range of ~0.1 to 1.0. We note that Ruffini et al. (GCN 18296) reached a similar conclusion independently. Fig1: http://104.167.114.70/gcns/grb150906b/fig1.png Fig2: http://104.167.114.70/gcns/grb150906b/fig2.png
• GCN Circular #18321
  D. Svinkin, D. Frederiks, and V. Pal'shin, on behalf of the Konus-Wind team, report:
  It was suggested by Levan et. al. (GCN 18263) that the short-duration, hard-spectrum, bright GRB 150906B (Golenetskii et al. GCN 18259) might be connected with the NGC 3313 galaxy group. Continuing the discussion on the possible origin of GRB 150906B (Ruffini et al. GCN 18296 and F. Zhang et al. GCN 18298) we present a further analysis of the KW data for this GRB.
  Among ~300 bursts from the Konus catalog of short GRBs (Svinkin et al., in preparation), GRB 150906B is within top 25% in the terms of 16-ms peak energy flux and within top 3% in the terms of the total energy fluence, both in the 20 keV - 10 MeV range. In the terms of Epeak (CPL model), the burst is within 25% hardest GRBs in the sample.
  However, the burst duration is rather long T50=0.952+/-0.036 s (T90 = 1.642+/-0.076 s). The position of the GRB 150906B in the hardness-duration diagram (logT50-logHR32) of 1143 KW bright GRBs cannot exclude that the burst comes from the long GRB population. The figure showing the hardness-duration diagram is available at http://www.ioffe.ru/LEA/GRBs/GRB150906_T31340/GRB150906B_T50HR.png The contours denote the 1, 2, and 3 sigma confidence regions for two-dimensional Gaussian distributions. The HR32 is the ratio of counts in the 200-760 keV and 50-200 keV bands accumulated during burst duration. The vertical dashed line at T50=0.6 s marks the boundary used by Svinkin et al. to distinguish between short and long KW GRBs.
  The spectral lag calculated between the KW 400-1500 keV and 25-100 keV band light curves (tau = 70+/-40 ms, 68% confidence level) is consistent, within 68% CL, with the KW lag distributions for both short and long GRBs.
  Thus, being hard enough, GRB 150906B cannot be unambiguously classified as a short/hard from the KW data.