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Broadband X-Ray Spectra of the Ultraluminous X-Ray Source Holmberg IX X-1 Observed with NuSTAR, XMM-Newton, and Suzaku

Walton, D. J. and Harrison, F. A. and Grefenstette, B. W. and Miller, J. M. and Bachetti, M. and Barret, D. and Boggs, S. E. and Christensen, F. E. and Craig, W. W. and Fabian, A. C. and Fuerst, F. and Hailey, C. J. and Madsen, K. K. and Parker, M. L. and Ptak, A. and Rana, V. and Stern, D. and Webb, N. and Zhang, W. W. (2014) Broadband X-Ray Spectra of the Ultraluminous X-Ray Source Holmberg IX X-1 Observed with NuSTAR, XMM-Newton, and Suzaku. Astrophysical Journal, 793 (1). Art. No. 21. ISSN 0004-637X.

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We present results from the coordinated broadband X-ray observations of the extreme ultraluminous X-ray source Holmberg IX X-1 performed by NuSTAR, XMM-Newton, and Suzaku in late 2012. These observations provide the first high-quality spectra of Holmberg IX X-1 above 10 keV to date, extending the X-ray coverage of this remarkable source up to ~30 keV. Broadband observations were undertaken at two epochs, between which Holmberg IX X-1 exhibited both flux and strong spectral variability, increasing in luminosity from L_X = (1.90 ± 0.03) × 10^(40) erg s^(–1) to L_X = (3.35 ± 0.03) × 10^(40) erg s^(–1). Neither epoch exhibits a spectrum consistent with emission from the standard low/hard accretion state seen in Galactic black hole binaries, which would have been expected if Holmberg IX X-1 harbors a truly massive black hole accreting at substantially sub-Eddington accretion rates. The NuSTAR data confirm that the curvature observed previously in the 3-10 keV bandpass does represent a true spectral cutoff. During each epoch, the spectrum appears to be dominated by two optically thick thermal components, likely associated with an accretion disk. The spectrum also shows some evidence for a nonthermal tail at the highest energies, which may further support this scenario. The available data allow for either of the two thermal components to dominate the spectral evolution, although both scenarios require highly nonstandard behavior for thermal accretion disk emission.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Harrison, F. A.0000-0003-2992-8024
Bachetti, M.0000-0002-4576-9337
Boggs, S. E.0000-0001-9567-4224
Madsen, K. K.0000-0003-1252-4891
Ptak, A.0000-0001-5655-1440
Rana, V.0000-0003-1703-8796
Stern, D.0000-0003-2686-9241
Additional Information:© 2014 American Astronomical Society. Received 2014 February 11; accepted 2014 July 7; published 2014 August 29. The authors would like to thank the referee for providing useful feedback, which helped to improve the manuscript. This research has made use of data obtained with the NuSTAR mission, a project led by the California Institute of Technology (Caltech), managed by the Jet Propulsion Laboratory (JPL) and funded by NASA, XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, and Suzaku, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research was supported under NASA grant No. NNG08FD60C, and has made use of the NuSTAR Data Analysis Software (NUSTARDAS), jointly developed by the ASI Science Data Center (ASDC, Italy) and Caltech (USA). We also made use of the NASA/IPAC Extragalactic Database (NED), which is operated by JPL, Caltech, under contract with NASA. Many of the figures included in this work have been produced with the Veusz plotting package:, written and maintained by Jeremy Sanders. DB and MB are grateful to the Centre National d’Etudes Spatiales (CNES) for funding their activities. Facilites: NuSTAR, XMM, Suzaku
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Subject Keywords:black hole physics; X-rays: binaries; X-rays: individual (Holmberg IX X-1)
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2014-34
Record Number:CaltechAUTHORS:20141003-071241370
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Official Citation:Broadband X-Ray Spectra of the Ultraluminous X-Ray Source Holmberg IX X-1 Observed with NuSTAR, XMM-Newton, and Suzaku D. J. Walton et al. 2014 ApJ 793 21
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50184
Deposited By: Ruth Sustaita
Deposited On:06 Oct 2014 02:39
Last Modified:10 Oct 2017 21:03

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