Four years of wide-field search for nanosecond optical transients with the TAIGA-HiSCORE Cherenkov array

TL;DR

Over four winter seasons, the TAIGA-HiSCORE Cherenkov array was used to search for rare nanosecond optical transients, setting upper flux limits but detecting no astrophysical candidates.

Contribution

This study demonstrates the application of the TAIGA-HiSCORE array for wide-field optical transient searches and provides new upper bounds on transient fluxes in the 2018-2022 period.

Findings

No astrophysical candidates detected.

Set upper flux limit of ~1×10⁻³ events/ster/h.

Validated the array's capability for transient searches.

Abstract

It has been previously demonstrated [Panov et al. Physics of Atomic Nuclei 84(2021)1037] that the TAIGA-HiSCORE Cherenkov array, originally built for cosmic ray physics and ultrahigh-energy gamma-ray astronomy studies using the extensive air shower method, can be used in conventional optical astronomy for wide-field searches for rare nanosecond optical transients of astrophysical origin. The FOV of the facility is on the scale of 1~ster, and it is capable of detecting very rare transients in the visible light range with fluxes greater than approximately 3000~quanta/m$^2$/10~ns (10~ns is the apparatus integration time) and pulse durations of 10\,ns. Among the potential sources of distant nanosecond optical transients are the evaporation of primary black holes, magnetic reconnection in the accretion disks of black holes, and signals from distant lasers of extraterrestrial civilizations. The paper describes the methods and results of the search for optical transients using the TAIGA-HiSCORE Cherenkov array from 2018 to 2022 (four winter seasons of data collection). No reliable astrophysical candidates for optical transients were found. We set an upper bound on the flux of the searched events as $\sim 1\times10^{-3}$\,events/ster/h.