Gamma-ray Burst 121225B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #14101
  D. Kocevski (NASA/GSFC U.), J. L. Racusin (NASA/GSFC) and E. Sonbas (Adiyaman Univ.), report on behalf of the Fermi-LAT team:
  The Fermi Large Area Telescope (LAT) detected emission from GRB 121225B (GBM trigger 378122456/121225417) at approximately 10:00:54 UT on December 25th, 2012.
  The burst location was at the edge of the the LAT field of view at an angle of ~65 degrees to the LAT boresight, and had a zenith angle of 92 degrees. No significant excess is seen using standard analysis procedures. The burst exited the nominal LAT field of view roughly ~100 s after the GBM trigger and remained above an angle of 70 degrees to the LAT boresight for at least the next 5000 s.
  Using the non-standard LAT Low Energy (LLE) data selection, over 100 counts above background were detected in a single FRED like pulse, peaking 20s after the GBM trigger and coinciding with the time of the GBM emission, with a significance of 10 sigma. This detection is due to low energy gamma-rays, below 75 MeV, and therefore has insufficient spatial resolution to provide a reliable LAT localization. Indeed, no events were observed above 75 MeV using the standard analysis classes.
  A GBM circular on GRB 121225B is forthcoming.
  The Fermi LAT point of contact for this burst is Daniel Kocevski (daniel.kocevski at nasa.gov).
  The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
• GCN Circular #14102
  D. Tierney (UCD) reports on behalf of the Fermi GBM Team:
  "At 10:00:53.58 UT on 25 December 2012, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 121225B (trigger 378122456 / 121225417). This GRB was also detected by the Fermi LAT (GCN 14101, Kocevski et al.)
  The on-ground calculated location, using the GBM trigger data, is RA = 310.45, DEC = -34.83 (J2000 degrees, equivalent to 20 h 41 m, -34 d 49'), with an uncertainty of 1.5 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 66 degrees.
  The GBM light curve has a multi-pulse time history with with the main emission complexes at 15 to 25 seconds and at 45 to 65 seconds. The duration (T90) is 58.5 +/- 0.8 s (50-300 keV). The time-averaged spectrum from T0-1.8 s to T0+73.0 s is best fit by a Band function with Epeak = 277.6 (+13.1/-12.4) keV, alpha = -1.08 (+0.02/-0.02), and beta = -2.14 (+0.05/-0.06).
  The event fluence (10-1000 keV) in this time interval is (7.16 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+22.0 s in the 10-1000 keV band is 23.6 +/- 0.4 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #14103
  K. Hurley and J. Goldsten, on behalf of MESSENGER GRNS 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,
  V. Connaughton, M. Briggs, C. Meegan, and V. Pelassa, 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 long-duration GRB 121225B has been observed by Fermi (GBM: trigger 363381140, Tierney, GCN Circ. 14102; LAT: Kocevski et al., GCN Circ. 14101), Konus-Wind, INTEGRAL (SPI-ACS), and MESSENGER (GRNS), so far, at about 36054 s UT (10:00:54).
  We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:

    ---------------------------------------------
     RA(2000), deg                 Dec(2000), deg
    ---------------------------------------------
    Center:
     308.913 (20h 35m 39s) -34.355 (-34d 21' 18")
    Corners:
     308.749 (20h 35m 00s) -30.606 (-30d 36' 21")
     308.950 (20h 35m 48s) -30.654 (-30d 39' 14")
     308.778 (20h 35m 07s) -38.039 (-38d 02' 19")
     308.567 (20h 34m 16s) -37.991 (-37d 59' 27")
    ---------------------------------------------
  

  The error box area is 1.3 sq. deg, and its maximum dimension is 7.4 deg (the minimum one is 0.2 deg, the minimum annulus width is 0.2 deg).
  This box can be improved.
  A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB121225_T36066/IPN/
• GCN Circular #14104
  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 intense long-duration hard-spectrum GRB 121225B (Fermi-LAT detection: Kocevski et al., GCN 14101; Fermi-GBM detection: Tierney et al., GCN 14102; IPN detection and localization: Hurley et al., GCN 14103) triggered Konus-Wind at T0=3D36066.467s UT (10:01:06.467)
  The burst light curve shows a hard multi-peaked structure from ~T0-18s to ~T0+15s followed by a softer complex pulse from ~T0+23s to ~T0+56s. The total duration of the burst is ~75s. The emission is seen up to 15 MeV.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB121225_T36066/
  As observed by Konus-Wind, the burst had a fluence of (9.0 =B1 0.7)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.288 s, of (9.9 =B1 0.9)x10-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The time-integrated spectrum of the burst (measured T0 to T0+55.296 s) is best fit in the 20 keV - 17 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -1.00 =B1 0.08, the high energy photon index beta =3D -2.3 =B1 0.1, the peak energy Ep =3D 230 =B1 20 keV, chi2 =3D 102.0/95 dof.
  The spectrum at the maximum count rate (measured T0 to T0+6.144 s) is best fit in the 20 keV - 17 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D +0.85 =B1 0.07, the high energy photon index beta =3D -2.3 =B1 0.1, the peak energy Ep =3D 410 =B1 40 keV, chi2 =3D 89.7/93 dof.
  All the quoted results are preliminary.
• GCN Circular #14138
  S. Sugimoto, M. Tashiro, Y. Terada, W. Iwakiri, T. Yasuda, K. Takahara, M. Asahina, S. Kobayashi, A. Sakamoto, Y. Ishida,H. Ueno, (Saitama U.), M. Akiyama, N. Ohmori, E. Mochinaga, M. Yamauchi (Univ. of Miyazaki), K. Yamaoka, M. Kokubun, T. Takahashi (ISAS/JAXA), Y. Hanabata, T. Kawano, K. Takaki, R. Nakamura, Y.Tanaka, M. Ohno, Y. Fukazawa (Hiroshima U.), S. Sugita (Nagoya U.), Y. E. Nakagawa (Waseda U.), Y. Urata, P. Tsai (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo), on behalf of the Suzaku WAM team, report:
  The long, IPN localized GRB 121225B (K. Hurley et al., GCN 14103) was detected by the the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 10:01:03.165 UT (=T0).
  The observed light curve shows double-peaked structure starting at T0-16s, ending at T0+70s with a duration (T90) of about 53 seconds. The fluence in 100 - 1000 keV was 4.80(+0.19/-0.25)x10^-5 erg/cm^2. The 1-s peak flux measured from T0+9s was 8.50 photons/cm^2/s in the same energy range.
  Preliminary result shows that the time-averaged spectrum from T0-16s to T0+70s is well fitted by a single power-law with a photon index of 2.17(+0.07/-0.07) (chi^2/d.o.f = 32.8/30). All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included.
  ----
  The light curves with 1-sec time resolution for this burst are appeared at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/untrig/grb_table.html