TITLE: GCN CIRCULAR NUMBER: 38631 SUBJECT: Konus-Wind detection of GRB 241204A (short/hard) DATE: 24/12/19 08:22:13 GMT FROM: Dmitry Svinkin at Ioffe Institute svinkin@mail.ioffe.ru

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 short-duration GRB 241204A (Fermi-LAT detection: Bissaldi et al., GCN 38436; Fermi-GBM detection: Godwin et al., GCN 38441) triggered Konus-Wind at T0=13159.909 s UT (03:39:19.909).

The burst light curve shows a single pulse which starts at ~T0 and has a total duration of ~0.1 s. The emission is seen up to ~7 MeV.

The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB241204_T13159/

As observed by Konus-Wind, the burst had a fluence of 6.20(-1.01,+1.11)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0+0.004 s, of 1.45(-0.34,+0.37)x10^-4 erg/cm2/s (both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst (measured from T0 to T0+0.064 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 = -1.22(-0.11,+0.12) and Ep = 3550(-1308,+4267) keV (pgstat = 62/73 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.62 (pgstat = 62/72 dof).

All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.

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