Patchy Accretion Disks in Ultraluminous X-ray Sources
Abstract
The X-ray spectra of the most extreme ultra-luminous X-ray sources - those with L ≥ 10^(40) erg s^(-1) remain something of a mystery. Spectral roll-over in the 5-10 keV band was originally detected in in the deepest XMM-Newton observations of the brightest sources; this is confirmed in subsequent NuSTAR spectra. This emission can be modeled via Comptonization, but with low electron temperatures (kT_e ≃ 2 keV) and high optical depths (T ≃ 10) that pose numerous difficulties. Moreover, evidence of cooler thermal emission that can be fit with thin disk models persists, even in fits to joint XMM-Newton and NuSTAR observations. Using NGC 1313 X-1 as a test case, we show that a patchy disk with a multiple temperature profile may provide an excellent description of such spectra. In principle, a number of patches within a cool disk might emit over a range of temperatures, but the data only require a two-temperature profile plus standard Comptonization, or three distinct blackbody components. A mechanism such as the photon bubble instability may naturally give rise to a patchy disk profile, and could give rise to super-Eddington luminosities. It is possible, then, that a patchy disk (rather than a disk with a standard single-temperature profile) might be a hallmark of accretion disks close to or above the Eddington limit. We discuss further tests of this picture, and potential implications for sources such as narrow-line Seyfert-1 galaxies (NLSy1s) and other low-mass active galactic nuclei (AGN).
Additional Information
© 2014 The American Astronomical Society. Received 2014 January 19; accepted 2014 March 6; published 2014 March 26. JMM acknowledges helpful conversations with Mitch Begelman, Jason Dexter, and Richard Mushotzky. This work was supported under NASA Contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA.Attached Files
Published - pdf.pdf
Submitted - 1403.1769.pdf
Files
Name | Size | Download all |
---|---|---|
md5:fb621d959d5d98337858eee65f134827
|
1.1 MB | Preview Download |
md5:cda80b451ea3e14d13b23756c109b928
|
980.6 kB | Preview Download |
Additional details
- Eprint ID
- 53160
- Resolver ID
- CaltechAUTHORS:20150105-080756612
- NASA
- NNG08FD60C
- NASA/JPL/Caltech
- Created
-
2015-01-06Created from EPrint's datestamp field
- Updated
-
2021-11-10Created from EPrint's last_modified field
- Caltech groups
- Space Radiation Laboratory, NuSTAR