GCN Circular 12329
Derek B. Fox (Penn State) reports: "The new R~16 mag optical source identified by Li & Filippenko (GCN 12328) in their follow-on observations of the recent Swift BAT image trigger 502415 / GRB 110905A (Pagani et al., GCN 12327), is almost certainly the optical counterpart to the recently-discovered X-ray transient MAXI J1836-194 (Negoro et al., ATel #3611). This likely black hole X-ray binary system has an associated optical (Kennea et al., ATel #3613), NIR (Rau, Greiner & Sudilovsky, ATel #3619) and radio (Miller-Jones et al., ATel #3628) counterpat with coordinate position (most accurately known from EVLA observations) consistent to <~1 arcsec with the optical source of Li & Fillippenko. Given that BAT trigger #502415 is a BAT image trigger with localization consistent with the position of the new transient, this raises the question of whether BAT trigger #502415 was generated by high-energy variability of MAXI J1836-194 itself rather than being due to a bona fide gamma-ray burst. If GRB 110905A is a genuine gamma-ray burst -- distinct from and unrelated to MAXI J1836-194 -- the source reported by Li & Fillippenko, being the optical counterpart of MAXI J1836-194, is almost certainly not the burst's optical afterglow. The author cites a private communication from J. Greiner as first to point out this possible interpretation of events."