TITLE:   GCN CIRCULAR
NUMBER:  37624
SUBJECT: Konus-Wind detection of GRB 240912A
DATE:    24/09/29 14:14:30 GMT
FROM:    Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>

D. Svinkin, D. Frederiks, M. Ulanov, A. Tsvetkova,
A. Lysenko, A. Ridnaia, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 240912A
(Fermi-GBM detection: The Fermi GBM Team, GCN 37465;
Smith and Meegan, GCN 37478;
Swift-BAT detection: Evans et al., GCN 37466;
Parsotan et al., GCN 37539;
INTEGRAL-SPI-ACS detection: Pawar et al., GCN 37473;
SVOM-GRM detection: Zheng et al., GCN 37484)
triggered Konus-Wind at T0 = 6454.746 s UT (01:47:34.746).

The burst light curve shows a multipeaked structure
which starts at ~T0-60 s and has a total duration of ~118 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/GRB240912_T06454/

As observed by Konus-Wind, the burst
had a fluence of 9.57(-0.96,+0.88)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+2.496 s,
of 7.32(-1.90,+1.87)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+60.928 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.36(-0.11,+0.12),
the high energy photon index beta = -2.44(-0.54,+0.18),
the peak energy Ep = 196(-27,+37) keV
(chi2 = 90/96 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 s to T0+6.144 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.12(-0.15,+0.16),
the high energy photon index beta = -2.59(-7.41,+0.35),
the peak energy Ep = 358(-77,+124) keV
(chi2 = 89/72 dof).

Assuming the redshift z=1.234 (de Ugarte Postigo et al., GCN 37469)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is 4.0(-0.4,+0.4)x10^53 erg,
the peak luminosity L_iso is 6.8(-1.8,+1.7)x10^52 erg/s,
the rest-frame peak energy of the time-averaged spectrum
Ep,i,z is 437(-60,+82) keV, and the spectrum near the maximum count rate
Ep,p,z is 799(-172,+277) keV.

With the obtained estimates, GRB 240912A is inside 68% prediction bands
for 'Amati' and 'Yonetoku' relations, for the sample of >300 long KW
GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), 
see http://www.ioffe.ru/LEA/GRBs/GRB240912_T06454/GRB240912A_rest_frame.pdf

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