Orphan optical flare as SOSS emission afterglow, localization in time

Lipunov, V.; Kornilov, V.; Zhirkov, K.; Tyurina, N.; Gorbovskoy, E.; Vlasenko, D.; Simakov, S.; Topolev, V.; Francile, C.; Podesta, R.; Podesta, F.; Svinkin, D.; Budnev, N.; Gress, O.; Balanutsa, P.; Kuznetsov, A.; Chasovnikov, A.; Serra-Ricart, M.; Gabovich, A.; Minkina, E.; Antipov, G.; Svertilov, S.; Tlatov, A.; Senik, V.; Tselik, Yu; Kechin, Ya; Yurkov, V.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society

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We report on MASTER optical observations of an afterglow-like optical and X-ray transient AT2021lfa/ZTF21aayokph. We detected the initial steady brightening of the transient at 7σ confidence level. This allowed us to use smooth optical self-similar emission of GRBs model to constrain the explosion time to better than 14 min as well as to estimate its initial Lorentz factor Γ0 = 20 ± 10. Taking into consideration the low Γ0 and non-detection in gamma-rays, we classify this transient as the first failed GRB afterglow.