TITLE: GCN CIRCULAR NUMBER: 39873 SUBJECT: Konus-Wind detection of GRB 250322A (short) DATE: 25/03/26 12:50:11 GMT FROM: Anna Ridnaia at Ioffe Institute ridnaia@mail.ioffe.ru
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The short-duration GRB 250322A (Swift-BAT detection: Gupta et al., GCN 39835; Sadaula et al., GCN 39867; AstroSat-CZTI detection: Tembhurnikar et al., GCN 39849) triggered Konus-Wind at T0=57974.215 s UT (16:06:14.215).
The burst light curve shows a multipeaked structure, which starts at T0-0.102 s and has a total duration of ~0.18 s.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250322_T57974/
As observed by Konus-Wind, the burst had a fluence of 1.02(-0.13,+0.14)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.086 s, of 1.05(-0.24,+0.25)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
Since the brightest peak of the burst light curve was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data.
Modelling the KW 3-channel time-integrated spectrum (measured from T0-0.102 s to T0+0.078 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = 0.22(-0.39,+0.52) and Ep = 472(-64,+85) keV.
Assuming the redshift z=0.42 (Fong et al., GCN 39852; Yang et al. GCN 39859) 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 4.9(-0.6,+0.7)x10^50 erg, the peak luminosity L_iso is 7.1(-1.6,+1.7)x10^51 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 670(-91,+121) keV.
With the obtained estimates, GRB 250322A is a clear outlier in the 'Amati' relation derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021). Meanwhile, in both Eiso-Ep,z and Liso-Ep,z planes, the GRB 250322A position is consistent with short-hard (Type I) GRB population, see http://www.ioffe.ru/LEA/GRBs/GRB250322_T57974/GRB250322A_rest_frame.pdf
All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.
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