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GCN Circular 30921

Subject
Konus-Wind detection of GRB 210928A
Date
2021-10-04T12:37:31Z (3 years ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
A. Ridnaia, D. Frederiks, S. Golenetskii, A. Lysenko,
D. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 210928A
(Fermi-LAT detection: Axelsson et al., GCN 30912;
Fermi-GBM observation: Fletcher & Meegan, GCN 30913)
triggered Konus-Wind at T0=7234.398 s UT (02:00:34.398).

The burst light curve shows a single multi-peaked pulse
started at ~T0-4.3 s with a total duration of ~27.3 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/GRB210928_T07234/

As observed by Konus-Wind, the burst
had a fluence of 6.79(-0.66,+0.71)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+14.416 s,
of 6.45(-1.72,+1.77)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+24.320 s)
is best fit in the 20 keV - 6 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.34(-0.15,+0.16),
the high energy photon index beta = -2.55(-0.35,+0.21),
the peak energy Ep = 361(-33,+38) keV
(chi2 = 61/78 dof).

The spectrum near the maximum count rate
(measured from T0+8.448 to T0+16.128 s)
is best fit in the 20 keV - 6 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.07(-0.21,+0.23),
the high energy photon index beta = -2.73(-0.55,+0.28),
the peak energy Ep = 328(-30,+36) keV
(chi2 = 75/78 dof).

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