GCN Circular 39375
Subject
Konus-Wind detection of GRB 250215A / EP250215a
Event
Date
2025-02-19T15:45:03Z (10 months ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
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 250215A / EP250215a
(Fermi-GBM detection: The Fermi GBM team, GCN 39327;
Scotton and Meegan, GCN 39342;
EP-WXT detection: Wang et al., GCN 39329;
INTEGRAL-SPI-ACS detection: Barria et al., GCN 39331;
AstroSat-CZTI detection: Tembhurnikar et al., GCN 39334;
SVOM/GRM detection: Zheng et al., GCN 39335)
triggered Konus-Wind at T0=09130.387 s UT (02:32:10.387).
The burst light curve shows a multipeaked structure
which starts at ~T0-14 s and has a total duration of ~22 s.
The emission is seen up to ~1 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250215_T09130/
As observed by Konus-Wind, the burst
had a fluence of 8.33(-1.97,+2.51)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+0.054 s,
of 5.12(-1.37,+1.66)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
Since a major part of the burst emission was detected
before the trigger time and the burst shows a minor spectral evolution,
we use the spectrum measured from T0 to T0+8.448 s
to estimate the total burst fluence.
This spectrum is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.03(-0.54,+0.69),
the high energy photon index beta = -2.31(-1.22,+0.30),
the peak energy Ep = 130(-36,+80) keV
(chi2 = 80/97 dof).
The spectrum near the maximum count rate
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 4 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.14(-0.74,+3.47),
the high energy photon index beta = -2.35(-0.68,+0.29),
the peak energy Ep = 118(-51,+53) keV
(chi2 = 18/17 dof).
Assuming the redshift z=4.61 (Sanchez-Ramirez et al., GCN 39343)
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 3.35(-0.79,+1.01)x10^53 erg,
the peak luminosity L_iso is 1.15(-0.31,+0.37)x10^54 erg/s,
the rest-frame peak energy of the time-averaged spectrum
Ep,i,z is 660(-250,+298) keV.
With the obtained estimates, GRB 250215A is inside 68% prediction band for
the 'Amati' and 90% - for the 'Yonetoku' relations derived 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/GRB250215_T09130/GRB250215A_rest_frame.pdf
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.