TITLE: GCN CIRCULAR NUMBER: 43013 SUBJECT: Konus-Wind detection of GRB 251118A DATE: 25/12/06 16:38:47 GMT FROM: Valentina Panteleeva at Ioffe Institute panteleevav228@gmail.com
V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long-duration GRB 251118A (Fermi-GBM detection: The Fermi GBM team, GCN 42743; Palafox and Meegan, GCN 42783; BALROG localization: Preis and Greiner, GCN 42745; Fermi-LAT detection: Gupta and Khalil, GCN 42752; GECAM-B detection: Ren et al., GCN 42779; Glowbug detection: Cheung et al., GCN 42784) triggered Konus-Wind at T0=73904.449 s UT (20:31:44.449).
The burst light curve starts, at ~T0-20.5 s, with a short soft initial pulse (precursor) which had a duration of about 25.8 s. The precursor is followed, starting at ~T0+32 s, by the main episode, lasting for ~25 s. The total duration of the burst is ~48 s. The emission in the main episode is seen up to ~3 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251118_T73904/
As observed by Konus-Wind, the burst had the total fluence of 1.07(-0.03,+0.03)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+35.776 s, of 2.03(-0.15,+0.15)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the initial pulse (measured from T0 to T0+8.448 s) is best described 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 = -1.94(-0.03,+0.12) and Ep < 41 keV (chi2 = 89/85 dof). Fitting this spectrum by a GRB (Band) model results in the same estimates of alpha and Ep, and gives only an upper limit on the high energy photon index beta of -2.8 (chi2 = 89/84 dof).
The time-averaged spectrum of the main episode (measured from T0+33.024 to T0+65.536 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.29(-0.03,+0.04), the high energy photon index beta = -2.56(-0.08,+0.07), the peak energy Ep = 154(-5,+5) keV (chi2 = 110/97 dof).
The spectrum near the maximum count rate (measured from T0+33.024 to T0+36.608 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.74(-0.05,+0.06), the high energy photon index beta = -2.53(-0.10,+0.08), the peak energy Ep = 251(-12,+12) keV (chi2 = 68/69 dof).
All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.
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