TITLE: GCN CIRCULAR NUMBER: 39019 SUBJECT: Konus-Wind detection of GRB 250118B DATE: 25/01/23 20:34:26 GMT FROM: Anna Ridnaia at Ioffe Institute ridnaia@mail.ioffe.ru
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long-duration GRB 250118B (IPN triangulation: Kozyrev et al., GCN 39017) triggered Konus-Wind at T0=13107.725 s UT (03:38:27.725).
The burst light curve shows a multipeaked structure, which starts at ~T0-5.8 s and has a total duration of ~9.4 s. We note a weaker and softer pulse seen in the same KW detector before the main pulse, from ~T0-58.8 s to ~T0-55.9 s. Since this pulse was detected by KW only, its relation to GRB 250118B cannot be currently confirmed. The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250118_T13107/
As observed by Konus-Wind, the burst had a fluence of 3.49(-0.35,+1.30)x10^-6 erg/cm^2 and a 64-ms peak flux, measured from T0-0.244 s, of 2.97(-0.60,+1.22)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
Since a major part of the burst emission was detected before the trigger time, the spectral analysis was performed using the KW 3-channel light curve data.
Modelling the KW 3-channel time-integrated spectrum (measured from T0-5.837 s to T0+3.552 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = -1.55(-0.14,+0.18) and Ep = 287(-95,+256) keV.
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
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