1995A&A...294..177G

Spectroscopic observations provide evidence that the optical transient object observed in 1966 on archival plates of Sonneberg Observatory is a B=18.5 dMe star. For an assumed flare duration of 40min. (or longer) the flare amplitude was {DELTA}m_B≃5.2mag. If the recorded event was belonging to the class of "fast" flares its amplitude could have reached 7-9mag. We estimate a lower limit for the optical flare energy release of 10³⁵(d/100 pc)²erg/s. We discuss the positional coincidence of this large amplitude flaring star with the error box of the γ-ray burst 1978 October 6B and conclude that the flare star is probably not related to the γ-ray burst. The fact that no other optical flare was found from this object restricts their frequency to be less than 7x10^–4h^–1 for amplitudes (in B) greater than 4.5mag. Nevertheless, large amplitude flares constitute a serious background problem for the wide field search for possible optical counterparts of γ-ray bursters.