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arXiv · 1508.07651

Spectroscopic Studies of an Ultraluminous Supersoft X-Ray Source in M81

Yu Bai·JiFeng Liu·Song Wang
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Abstract

Ultraluminous supersoft X-ray sources (ULSs) exhibit supersoft X-ray spectra with blackbody temperatures below 0.1 keV and bolometric luminosities above 10$^{39}$ ergs s$^{-1}$. In this Letter, we report the first optical spectroscopic observations of a ULS in M81 using the LRIS spectrograph on the Keck I telescope. The detected Balmer emission lines show a mean intrinsic velocity dispersion of 400$\pm$80 km s$^{-1}$, which is consistent with that from an accretion disk. The spectral index of the continuum on the blue side is also consistent with the multi-color disk model. The H$_{\alpha}$ emission line exhibits a velocity of $\sim$180 km s$^{-1}$ relative to the local stellar environment, suggesting that this ULS may be a halo system in M81 belonging to an old population. No significant shift is found for the H$_{\alpha}$ emission line between two observations separated by four nights.

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Yu Bai, JiFeng Liu, Song Wang. 2015-08-31. Spectroscopic Studies of an Ultraluminous Supersoft X-Ray Source in M81. https://doi.org/10.1088/2041-8205%2F802%2F2%2Fl27

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