FRB 20250316A: Upper limits from Konus-Wind observations

ATel #17090; A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team
on 19 Mar 2025; 16:51 UT
Credential Certification: Anna Kozlova (ridnaia@mail.ioffe.ru)

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Konus-Wind (KW, Aptekar et al., 1995) was observing the whole sky at the time of the FRB 20250316A (2025-03-16 08:33:46.657 UTC (topocentric at infinite frequency), hereafter T0; Mason Ng et al., ATel #17081; Calvin Leung et al., ATel #17086).

No triggered or waiting-mode KW events happened during ~19 hours before T0. The first event detected after T0 is GRB 250316A, ~26 minutes after T0, which localization is inconsistent with FRB 20250316A (Ronchini et al., GCN 39744). Using waiting-mode data within the interval T0 +/- 200 s, we found no significant (> 5 sigma) excess over the background in both KW detectors on temporal scales from 2.944 s to 100 s.

We estimate upper limits (90% conf.) on the 20 - 1500 keV fluence to 4.6x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a typical KW short GRB spectrum (an exponentially cut off power law (CPL) with alpha =-0.5 and Ep=500 keV) and to 1.7x10^-7 erg/cm^2 for a burst having spectrum similar to that of SGR/FRB 200428 (a CPL with alpha =-0.72 and Ep=85 keV). For a typical long GRB spectrum (the Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding limiting peak flux is 1.3x10^-7 erg/cm^2/s (20 - 1500 keV, 2.944 s scale).

Assuming the distance of ~40 Mpc to the probable host galaxy NGC 4141 (ATel #17081; ATel #17086) we estimate the following upper limits on the event hard-energy emission (20-1500 keV): the isotropic-equivalent energy release Eiso (~8.7x10^46 erg) and the peak luminosity Liso (~3.0x10^46 erg/s) , both in the range of bright extragalactic magnetar giant flares (Svinkin et al. 2021, Nature 589, 211).

All the quoted values are preliminary.