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GCN Circular 34403

Subject
Konus-Wind detection of GRB 230812B
Date
2023-08-13T12:39:29Z (6 months ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
legacy email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long very bright GRB 230812B (Fermi GBM detection:
Lessage et al., GCN 34387; Roberts et al., GCN 34391;
Fermi LAT detection: Scotton et al., GCN 34392;
GECAM-C observation: Xiong et al., GCN 34401;
AGILE/MCAL detection: Casentini et al., GCN 34402)
triggered Konus-Wind (KW) at T0=68292.611 s UT (18:58:12.611).

The burst light curve shows a single smooth emission pulse,
which starts at ~T0-0.1 s, peaks at ~T0+0.7 s,
and has a total duration of ~20 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB230812_T68292/

As observed by Konus-Wind, the burst had
a fluence of (3.27 ± 0.07)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 0.704 s,
of (2.63 ± 0.11)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+19.712 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.85 (-0.03,+0.03),
the high energy photon index beta = -2.38 (-0.05,+0.04),
the peak energy Ep = 288 (-12,+12) keV,
chi2 = 169/97 dof.

The spectrum near the peak count rate (measured from T0+0.512 to T0+0.768 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.17 (-0.08,+0.09),
the high energy photon index beta = -2.65 (-0.14,+0.11),
the peak energy Ep = 444 (-30,+31) keV,
chi2 = 68/56 dof.

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.


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