X-Ray Outflows and Super-Eddington Accretion in the Ultraluminous X-Ray Source Holmberg IX X-1

Walton, D.J.; Miller, J.M.; Harrison, F.A.; Fabian, A.C.; Roberts, T.P.; Middleton, M.J.; Reis, R.C.

Abstract

Studies of X-ray continuum emission and flux variability have not conclusively revealed the nature of ultraluminous X-ray sources (ULXs) at the high-luminosity end of the distribution (those with LX 1040 erg s−1). These are of particular interest because the luminosity requires either super-Eddington accretion onto a black hole of mass ∼10 M or more standard accretion onto an intermediate-mass black hole. Super-Eddington accretion models predict strong outflowing winds, making atomic absorption lines a key diagnostic of the nature of extreme ULXs. To search for such features, we have undertaken a long, 500 ks observing campaign on Holmberg IX X-1 with Suzaku. This is the most sensitive data set in the iron K bandpass for a bright, isolated ULX to date, yet we find no statistically significant atomic features in either emission or absorption; any undetected narrow features must have equivalent widths less than 15–20 eV at 99% confidence. These limits are far below the 150 eV lines expected if observed trends between mass inflow and outflow rates extend into the super-Eddington regime and in fact rule out the line strengths observed from disk winds in a variety of sub-Eddington black holes. We therefore cannot be viewing the central regions of Holmberg IX X-1 through any substantial column of material, ruling out models of spherical super-Eddington accretion. If Holmberg IX X-1 is a super-Eddington source, any associated outflow must have an anisotropic geometry. Finally, the lack of iron emission suggests that the stellar companion cannot be launching a strong wind and that Holmberg IX X-1 must primarily accrete via Roche-lobe overflow.

Citation

Walton, D., Miller, J., Harrison, F., Fabian, A., Roberts, T., Middleton, M., & Reis, R. (2013). X-Ray Outflows and Super-Eddington Accretion in the Ultraluminous X-Ray Source Holmberg IX X-1. Astrophysical Journal Letters, 773(1), Article L9. https://doi.org/10.1088/2041-8205/773/1/l9

• Journal Article Type: Article
• Publication Date: Aug 1, 2013
• Deposit Date: Sep 11, 2013
• Publicly Available Date: Jan 28, 2014
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Electronic ISSN: 2041-8213
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 773
• Issue: 1
• Article Number: L9
• DOI: https://doi.org/10.1088/2041-8205/773/1/l9
• Keywords: Black hole, Physics, X-rays, Binaries, Holmberg IX X-1.
• Public URL: https://durham-repository.worktribe.com/output/1478292