2009CBET.1774....2K

K. Kinugasa, S. Honda, and O. Hashimoto, Gunma Astronomical Observatory (GAO); and T. Kato, H. Maehara, and D. Nogami, Kyoto University, report that they observed ASAS J150946-2147.7 with the GAO 1.5-m telescope (+ Gunma Low- resolution Spectrograph, GLOWS; resolution about 400; range 400-800 nm) on Apr. 7, 9, 10, and 15. The spectra showed strong emission lines of He II at 468.6 nm, C III/N III at 464.0 nm, and weaker He I emission lines superimposed on a late-A-type stellar spectrum. These emission lines and stellar absorption lines showed radial-velocity variations with measured amplitudes of about 110 km/s and 200 km/s (respectively) out of phase, suggesting that the emission lines arise from an accretion disk around a black hole of 3-5 solar masses. The ASAS J150946-2147.7 system is remarkably similar to the binary components of the unusual microquasar V4641 Sgr (IAUC 7440; Orosz et al. 2001, Ap.J. 555, 489). Since the large, superluminal 1999 outburst of V4641 Sgr (IAUC 7253, 7254, 7256, 7257, 7263, 7265, 7267) was preceded by enhanced optical activity for months (IBVS 4777), the present active state might lead to a similar giant outburst. Close monitoring and observations at other wavelengths are strongly encouraged.