Holmberg IX X-1 is a well-known ultraluminous X-ray source with an X-ray luminosity of ~1e40 erg/s. The source has been monitored by the X-ray Telescope of Swift regularly. Since 2009 April, the source has been in an extended low luminosity state. We utilize the co-added spectra taken at different luminosity states to study the spectral behavior of the source. Simple power-law and multi-color disk blackbody models can be ruled out. The best overall fits, however, are provided by a dual thermal model with a cool blackbody and a warm disk blackbody. This suggests that Holmberg IX X-1 may be a 10 solar-mass black hole accreting at 7 times above the Eddington limit or a 100 solar-mass maximally rotating black hole accreting at the Eddington limit, and we are observing both the inner regions of the accretion disk and outflows from the compact object.
@article{arxiv.1009.0275,
title = {Swift observations of the ultraluminous X-ray source Holmberg IX X-1},
author = {A. K. H. Kong and Y. J. Yang and T. -C. Yen and H. Feng and P. Kaaret},
journal= {arXiv preprint arXiv:1009.0275},
year = {2015}
}
Comments
6 pages, 2 figures; accepted for publication in ApJ