The nature of ULX source M101 X-1: Optically thick outflow from a stellar mass black hole

Rong Feng Shen*, Rodolfo Barniol Duran, Ehud Nakar, Tsvi Piran

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The nature of ultraluminous X-ray sources (ULXs) has long been plagued by an ambiguity about whether the central compact objects are intermediate-mass (IMBH,≳103M) or stellarmass (a few tens M) black holes (BHs). The high-luminosity ({reversed tilde equals}1039 erg s-1) and supersoft spectrum (T {reversed tilde equals} 0.1 keV) during the high state of the ULX source X-1 in the galaxy M101 suggest a large emission radius (≳109 cm), consistent with being an IMBH accreting at a sub-Eddington rate. However, recent kinematic measurement of the binary orbit of this source and identification of the secondary as a Wolf-Rayet star suggest a stellar-mass BH primary with a super-Eddington accretion. If that is the case, a hot, optically thick outflow from the BH can account for the large emission radius and the soft spectrum. By considering the interplay of photons' absorption and scattering opacities, we determine the radius and mass density of the emission region of the outflow and constrain the outflow mass-loss rate. The analysis presented here can be potentially applied to other ULXs with thermally dominated spectra, and to other super-Eddington accreting sources.

Original languageEnglish
Pages (from-to)L60-L64
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - 1 Jan 2015


FundersFunder number
Seventh Framework Programme279369


    • Black holes - stars
    • Individual
    • M101 X-1
    • Opacity - scattering - stars
    • Outflows -X-rays
    • Winds


    Dive into the research topics of 'The nature of ULX source M101 X-1: Optically thick outflow from a stellar mass black hole'. Together they form a unique fingerprint.

    Cite this