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MAXI J1932+091/Swift J193310.4+091141: Optical counterpart with emission lines

ATel #6186; R. Itoh, K. Kawaguchi, Y. Moritani, (Hiroshima Univ.), O. Hashimoto (Gunma Astronomical Observatory), K. Kinugasa (NAOJ), K. Morihana, J. Takahashi, Y. Itoh (Univ. of Hyogo), M. Imai, M. Watanabe (Hokkaido Univ.), D. Nogami (Kyoto Univ.) and N. Kawai (Tokyo Tech) on behalf of the OISTER collaboration
on 30 May 2014; 15:27 UT
Credential Certification: Nobuyuki Kawai (nkawai@phys.titech.ac.jp)

Subjects: Optical, X-ray, Binary, Neutron Star, Star, Transient

We performed low-resolution optical spectroscopy of the optical counterpart of Swift J193310.4+091141 (Kennea et al., ATEL #6177), and also the likely counterpart of the X-ray flaring source MAXI J1932+091 (Yamaoka et al., ATEL #6174, Morii et al. ATEL #6184 ). The observations have been performed at Gunma Astronomical Observatory, Nishi-Harima Astronomical Observatory, Higashi-Hiroshima Observatory, and Hokkaido University, during the night of May 29 between 12:59 and 16:22 UT. In the spectra, we detected a strong H-alpha emission line and an H-beta line. There are no strong emission lines other than these hydrogen Balmer lines. If this object is associated with the X-ray flare source MAXI J0932+091, this result, combined with the X-ray spectra, seems to suggest the nature of the source to be an X-ray binary comprising a compact object and a Be star. Absence of forbidden lines such as [O III] or [O I] seems to exclude classification of this source to other classes of X-ray flare sources, such as a symbiotic star or a protostar. Absence of conspicuous absorption lines excludes late-type systems such as RS CVn and dMe stars. Absence of He lines favors a Be circumstellar envelope over an accretion disk around a compact object as the source of the optical emission lines. In addition, ultraviolet detection with the Swift/UVOT despite of the absorbed X-ray spectrum (Kennea et al., ATEL #6177) suggests that the absorption is local to the compact X-ray source, but is not affecting the optical source. We note, however, that the reported proper motion (thus implying a small distance to the source) may be inconsistent with a Be star interpretation, and a further examination is required. This work is supported by the Optical & Near-Infrared Astronomy Inter-University Cooperation Program, the MEXT of Japan.