Gamma-ray Burst 150126A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #17352
  T. Takagi (RIKEN), S. Nakahira (JAXA), M. Serino (RIKEN), H. Negoro (Nihon U.), S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Morii, J. Sugimoto, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, T. Namba, M. Fujita, F. Honda (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:
  The MAXI/GSC nova alert system triggered an uncatalogued X-ray transient source at 21:03:24 UT. Assuming that the source flux was constant over the transit, we obtain the source position at
  (R.A., Dec) = (350.503 deg, -12.368 deg) = (23 22 00, -12 22 04) (J2000)
  with a statistical 90% C.L. elliptical error region with long and short radii of 0.56 deg and 0.46 deg respectively. The roll angle of long axis from the north direction is 145.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 55 +- 17 mCrab (4-10keV, 1 sigma error). There was no significant excess flux in the previous transit at UT 19:30 and in the next transit at 22:35 UT with an upper limit of 20 mCrab for each.
  This position is about 2 degree from the position of the Fermi trigger #443998238. Considering the Fermi detection, the transit time, and the spectral softness, the source is likely to be the afterglow of the GRB triggered by Fermi.
• GCN Circular #17353
  Matthew Stanbro (UAH) reports on behalf of the Fermi GBM Team:
  "At 20:50:35.78 UT on 26 January 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150126A (trigger 443998238 / 15012686) which MAXI detected an afterglow candidate (Takagi et al. 2015, GCN 17352). The GBM on-ground location is consistent with MAXI position.
  The angle from the Fermi LAT boresight is 92 degrees.
  The GBM light curve consists of 2 main episodes with a duration (T90) of about 97 s (50-300 keV). The time-averaged spectrum from T0-2.05 s to T0+91.14 s is best fit by a Band function with Epeak = 217 +/- 17 keV, alpha = -1.07 +/- 0.04, and beta = -2.45 +/- 0.22
  The event fluence (10-1000 keV) in this time interval is (2.55 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+71.3 s in the 10-1000 keV band is 9.71 +/- 0.36 ph/s/cm^2.
  A power law function with an exponential high-energy cutoff fits the spectrum equally well. The power law index is -1.11 +/- 0.03 and the cutoff energy, parameterized as Epeak, is 240 +/- 13 keV.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #17357
  Konus-Wind observation of GRB 150126 reveals its ultra-long
  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 GRB 150126A (MAXI/GSC detection: Takagi et al., GCN 17352; Fermi-GBM detection: Stanbro, GCN 17353) triggered Konus-Wind at T0=75103.524 s UT (20:51:43.524).
  The burst light curve shows several multi-peak emission episodes started at ~T0-800 s with a total duration of ~870 s; the last, most intense pulse triggered Konus-Wind. There is a hint of low-level ongoing emission in the soft energy band G1 (~83-360 keV) out to about T0+230 s. The K-W light curve and the K-W ecliptic latitude response confirm a common origin of all episodes. The position of the burst (Takagi et al., GCN 17352) was below the horizon for Fermi until ~20:50 UT (=T0(KW)-103 s), so it missed all emission episodes except the last one.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150126_T75103/
  As observed by Konus-Wind, the burst had a fluence of 8.56(-0.88,+1.30)x10^-5 erg/cm2, and a 1024-ms peak flux, measured from T0+8.288 s, of 1.03(-0.23,+0.24)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The spectrum of the triggered part of the burst (measured from T0 to T0+24.832 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 = -1.04(-0.28,+0.33) and Ep = 208(-36,+57) keV (chi2 = 74/60 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < 2.1 (chi2 = 74/59 dof)
  All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
  The burst duration, light curve shape, and energetics are similar to those of other multi-episode ultra-long GRBs with durations of ~1-2 ks (e.g. GRB 020410A, GRB 080407A, GRB 091024A, GRB 110709B - see Virgili et al. (2013), ApJ, 778:54 and references therein).