XMMU J010147.5-715550, another luminous supersoft X-ray source with a Be optical counterpart

ATel #9719; Valentina Cracco and Stefano Ciroi (Dept. of Physics and Astronomy, University of Padova, Italy), Marina Orio (Istituto Nazionale di Astrofisica, Padova, Italy, and Dept. of Astronomy, University of Wisconsin Madison, USA), Encarni Romero Colmenero (South African Astronomical Observatory, Cape Town, South Africa), and Jay Gallagher and Ralf Kotulla (Dept. of Astronomy, University of Wisconsin Madison, USA)
on 6 Nov 2016; 14:38 UT
Credential Certification: Marina Orio (orio@astro.wisc.edu)

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The Small Magellanic Cloud putative B star suggested to be the optical counterpart of the transient or recurrent XMM supersoft X-ray source XMMU J010147.5-715550 (Sturm et al., 2012, A&A 57, 76) was observed by us on September 7th, 2016 (JD 2457640.5) with the Southern African Large Telescope (SALT) at the South African Astronomical Observatory (SAAO) and the Robert Stobie Spectrograph (RSS), equipped with the PG0900 grating in longslit mode, with a slit width of 1 arcsecond. The spectral resolution is 4.5 Angstrom, the wavelength range is 3700-9000 Angstrom and the dispersion 0.96 Angstrom/pixel. The resulting spectrum was extracted, wavelength-calibrated and flux-calibrated using the spectrophotometric standard star LTT6248. We measured a steep blue continuum and emission lines of hydrogen (Balmer H alpha, H beta and H gamma), of He I (5876, 6678 and 7065 Angstrom), and of Fe II lines (at 4253, 5018 and 5317 Angstrom). The line width of the Balmer and He I lines is of about 360 km/s, and the lines' centers are red-shifted by about 190 km/s, which is consistent with SMC membership (assuming SMC systemic velocity of 158 km/s, Richter et al. 1987, A&A 171, 33). We suggest that these measurements imply that the optically luminous companion of the X-ray binary is indeed a Be star. This is the fourth case of a spectroscopically classified Be star associated with a likely hydrogen burning white dwarf in the Magellanic Clouds. The others are the supersoft X-ray sources RX J0527.8-6954 and XMMU J052016.0 in the LMC (Oliveira et al. 2010, A&A, 517, L5; Kabaka et al. 2006, A&A, 458,285), and the SMC source XMMU J052016.0 (Li et al. 2012, ApJ, 761, 99). The fluxes in the emission lines of XMMU J010147.5-715550, normalized to the H beta flux of 6.42 x 10(-15) erg/s, are given here after the name and/or wavelength in Angstrom of each emission line: H gamma 0.16, H beta 1.0, H alpha 5.22, He I 5876 0.16, Fe 4523 0.24, Fe 5018 0.20, FeII 5317 0.09, He I 6678 0.05, He I 7065 0.15.