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Patchy Accretion Disks in Ultraluminous X-ray Sources

Miller, J. M. and Bachetti, M. and Barret, D. and Harrison, F. A. and Fabian, A. C. and Webb, N. A. and Walton, D. J. and Rana, V. (2014) Patchy Accretion Disks in Ultraluminous X-ray Sources. Astrophysical Journal Letters, 785 (1). Art. No. L7. ISSN 2041-8205. doi:10.1088/2041-8205/785/1/L7.

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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).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bachetti, M.0000-0002-4576-9337
Barret, D.0000-0002-0393-9190
Harrison, F. A.0000-0003-2992-8024
Fabian, A. C.0000-0002-9378-4072
Walton, D. J.0000-0001-5819-3552
Rana, V.0000-0003-1703-8796
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.
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
Subject Keywords:accretion disks, black hole physics, X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20150105-080756612
Persistent URL:
Official Citation:Patchy Accretion Disks in Ultra-luminous X-Ray Sources J. M. Miller et al. 2014 ApJ 785 L7
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53160
Deposited By: Ruth Sustaita
Deposited On:06 Jan 2015 19:38
Last Modified:10 Nov 2021 19:48

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