TITLE: GCN CIRCULAR NUMBER: 38727 SUBJECT: Konus-Wind detection of GRB 241228A DATE: 24/12/30 11:44:36 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 241228A (Swift-BAT detection: D'Elia et al., GCN 38681; Sadaula et al., GCN 38701; Fermi-GBM detection: Scotton & Meegan, GCN 38695) triggered Konus-Wind at T0=14233.924 s UT (03:57:13.924).

The burst light curve shows a two-peak structure which starts at ~T0-0.2 s and has a total duration of ~5.1 s. 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/GRB241228_T14233/

As observed by Konus-Wind, the burst had a fluence of 3.35(-0.17,+0.18)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0+1.760 s, of 1.74(-0.01,+0.01)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst (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 = -0.88(-0.24,+0.26) and Ep = 75(-5,+5) keV (chi2 = 96/81 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 96/80 dof).

All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.

View this GCN Circular online at https://gcn.nasa.gov/circulars/38727. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...