TITLE: GCN CIRCULAR NUMBER: 39498 SUBJECT: Konus-Wind detection of GRB 250225B DATE: 25/02/26 18:14:00 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 250225B (Swift-BAT detection: Williams et al., GCN 39473; SVOM/GRM detection: Zhang et al., GCN 39493) triggered Konus-Wind at T0=70750.895 s UT (19:39:10.895).
The burst light curve shows a bright initial pulse which starts at ~T0-2.2 s and has a total duration of ~3.3 s, followed by two weaker emission episodes centered around ~T0+60 s and T0+108 s. The emission is seen up to ~6 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250225_T70750/
As observed by Konus-Wind, the burst had a fluence of 1.54(-0.18,+0.28)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.262 s, of 1.14(-0.24,+0.35)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 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 = -1.14(-0.16,+0.18) and Ep = 634(-181,+393) keV (chi2 = 66/84 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 66/83 dof).
The time-averaged spectrum of the second emission episode (measured from T0+57.600 to T0+65.792 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model with alpha = -1.23(-0.21,+0.28) and Ep = 361(-118,+292) keV (chi2 = 97/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 95/98 dof).
The time-averaged spectrum of the third emission episode (measured from T0+106.752 to T0+114.944 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model with alpha = -0.91(-0.69,+1.12) and Ep = 187(-74,+228) keV (chi2 = 110/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 110/98 dof).
All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.
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