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arXiv · 2303.11639

Identification of a Helium Donor Star in NGC 247 ULX-1

Changxing Zhou·Hua Feng·Fuyan Bian
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Abstract

With Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) observations, we detected highly variable helium emission lines from the optical counterpart of the supersoft ultraluminous X-ray source (ULX) NGC 247 ULX-1. No Balmer lines can be seen in the source spectrum. This is the first evidence for the presence of a helium donor star in ULXs, consistent with a prediction that helium donor stars may be popular in ULXs. The helium lines with a FWHM of about 200 km/s are likely produced on the outer accretion disk. Their strong variation implies that the central X-ray source can be significantly obscured to the outer disk. Also, a ring or a double-ring structure is revealed in the MUSE image. It is unknown whether or not it is related to the progenitor of the ULX binary.

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Changxing Zhou, Hua Feng, Fuyan Bian. 2023-03-21. Identification of a Helium Donor Star in NGC 247 ULX-1. https://doi.org/10.3847/1538-4357%2Facc5eb

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