Gamma-ray Burst 170904A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #21817
  Z. W. Li, J. Y. Liao, C. K. Li, X. B. Li, S. L. Xiong, C. Z. Liu, X. F. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:
  During the commissioning phase, at 2017-09-04T09:46:00.62 (T0), Insight-HXMT detected GRB 170904A (trigger ID: HEB170904406) in a routine search of the data, which was also observed by INTEGRAL/SPI-ACS and Swift/BAT.
  The Insight-HXMT light curve consists of multiple pulses with a duration (T90) of 10.9 s measured from T0+0.1 s. The 1-s peak rate, measured from T0+1.0 s, is 4655.1 cnts/sec. The total counts from this burst is 43647.2 counts.
  URL_LC: http://www.hxmt.org/images/GRB/HEB170904406_lc.jpg
  All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (record energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
  The analysis results presented above are preliminary; final results will be published elsewhere.
  Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org/index.php/enhome .
  
• GCN Circular #21820
  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,
  D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, A. Kozlova, 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,
  S. Barthelmy, J. Cummings, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team,
  X. B. Li, Y. Huang, Z. W. Li, and S. L. Xiong, on behalf of the Insight-HXMT team, and
  W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team, report:
  The long-duration, very bright GRB 170904A (Li et al., GCN Circ. 21817) was detected by Konus-Wind, INTEGRAL (SPI-ACS), Insight-HXMT (HE), Mars-Odyssey (HEND), and Swift (BAT) at about 35161 s UT (09:46:01). 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:
      35.374 (02h 21m 30s) -32.498 (-32d 29' 51")
    Corners:
      35.139 (02h 20m 33s) -34.082 (-34d 04' 56")
      35.438 (02h 21m 45s) -33.461 (-33d 27' 38")
      35.574 (02h 22m 18s) -30.892 (-30d 53' 32")
      35.302 (02h 21m 12s) -31.531 (-31d 31' 51")
    ---------------------------------------------
  

  The error box area is 1934 sq. arcmin, and its maximum dimension is 3.2 deg (the minimum one is 12.6 arcmin). The Sun distance was 125 deg.
  This box may be improved.
  A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB170904_T35162/IPN
  The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
• GCN Circular #21852
  A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline on behalf of the Konus-Wind team, report:
  The long-duration, hard-spectrum, bright GRB 170904A (IPN Triangulation: Hurley et al., GCN 21820) triggered Konus-Wind at T0=35162.28 s UT (09:46:02.280).
  The burst light curve shows multiple emission pulses in the interval from ~T0-56 s ~T0+30 s. The emission is seen up to ~19 MeV. Weak count rate increases are seen in the same S1 KW detector at ~T0-560 s and ~T0-350 s, however their attribution to this GRB is unclear.
  As observed by Konus-Wind, the burst had a fluence of 1.73(-0.09,+0.09)x10^-4 erg/cm2, and a 64-ms peak energy flux, measured from T0+11.728 s, of 1.90(-0.32,+0.32)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+22.016 s) is best fit in the 20 keV - 19 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.69(-0.05,+0.06), the high energy photon index beta = -2.17(-0.10,+0.08), the peak energy Ep = 466(-36,+40) keV, chi2 = 115/97 dof.
  The spectrum near the peak count rate (measured from T0+9.984 to T0+11.776 s) is best fit in the 20 keV - 19 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.73(-0.11,+0.13), the high energy photon index beta = -2.19(-0.24,+0.15), the peak energy Ep = 441(-72,+87) keV, chi2 = 53/67 dof.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB170904_T35162/
  All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.