A large amplitude aring dMe star in the 1978 October 6 B - ray burst error box ?

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 are duration of 40 min. (or longer) the are amplitude was 4m B 5.2 mag. If the recorded event was belonging to the class of 'fast' ares its amplitude could have reached 7-9 mag.. We estimate a lower limit for the optical are energy release of 10 35 (d/100 pc) 2 erg/s. We discuss the positional coincidence of this large amplitude aring star with the error box of the-ray burst 1978 October 6B and conclude that the are star is probably not related to the-ray burst. The fact that no other optical are was found from this object restricts their frequency to be less than 7210 04 h 01 for amplitudes (in B) greater than 4.5 mag. Nevertheless, large amplitude ares constitute a serious background problem for the wide eld search for possible optical counterparts of-ray bursters.