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The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342

Rana, Vikram R. and Harrison, Fiona A. and Bachetti, Matteo and Walton, Dominic J. and Furst, Felix and Barret, Didier and Miller, Jon M. and Fabian, Andrew C. and Boggs, Steven E. and Christensen, Finn C. and Craig, William W. and Grefenstette, Brian W. and Hailey, Charles J. and Madsen, Kristin K. and Ptak, Andrew F. and Stern, Daniel and Webb, Natalie A. and Zhang, William W. (2015) The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342. Astrophysical Journal, 799 (2). Art. No. 121. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20141210-150832641

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Abstract

We present results for two Ultraluminous X-ray Sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by ~ 7 days. We observe little spectral or ux variability above 1 keV between epochs, with unabsorbed 0.3-30 keV luminosities being 1.04^(+0.08)_(-0.06) x 10^(40) erg s^(-1) for IC 342 X-1 and 7.40 ± 0.20 x 10^(39) erg s^(-1) for IC 342 X-2, so that both were observed in a similar, luminous state. Both sources have a high absorbing column in excess of the Galactic value. Neither source has a spectrum consistent with a black hole binary in low/hard state, and both ULXs exhibit strong curvature in their broadband X-ray spectra. This curvature rules out models that invoke a simple reflection-dominated spectrum with a broadened iron line and no cutoff in the illuminating power-law continuum. X-ray spectrum of IC 342 X-1 can be characterized by a soft disk-like black body component at low energies and a cool, optically thick Comptonization continuum at high energies, but unique physical interpretation of the spectral components remains challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot (3.8 keV) accretion disk, or a Comptonized continuum with no indication of a seed photon population. Although the seed photon component may be masked by soft excess emission unlikely to be associated with the binary system, combined with the high absorption column, it is more plausible that the broadband X-ray emission arises from a simple thin blackbody disk component. Secure identification of the origin of the spectral components in these sources will likely require broadband spectral variability studies.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/799/2/121DOIArticle
http://iopscience.iop.org/0004-637X/799/2/121PublisherArticle
http://arxiv.org/abs/1401.4637arXivDiscussion Paper
ORCID:
AuthorORCID
Rana, Vikram R.0000-0003-1703-8796
Harrison, Fiona A.0000-0003-2992-8024
Bachetti, Matteo0000-0002-4576-9337
Walton, Dominic J.0000-0001-5819-3552
Boggs, Steven E.0000-0001-9567-4224
Madsen, Kristin K.0000-0003-1252-4891
Ptak, Andrew F.0000-0001-5655-1440
Stern, Daniel0000-0003-2686-9241
Additional Information:© 2015 American Astronomical Society. Received 2014 January 20; accepted 2014 November 14; published 2015 January 21. This work was supported under NASA No. NNG08FD60C, and made use of data from the Nuclear Spectroscopic Telescope Array (NuSTAR) mission, a project led by Caltech, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration, and XMM-Newton, an ESA mission. We would like to thank the anonymous referee for his positive comments to improve quality of this paper. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and Caltech (USA). D. Barret and M. Bachetti are grateful to the Centre National d'Etudes Spatiales (CNES) for funding their activities.
Group:NuSTAR, Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASANNG08FD60C
NASA/Caltech/JPLUNSPECIFIED
Centre National d'Etudes Spatiales (CNES)UNSPECIFIED
Subject Keywords:accretion, accretion disks, black hole physics, X-rays: binaries { X-rays: individual (IC 342 X-1, IC 342 X-2)
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-84
Record Number:CaltechAUTHORS:20141210-150832641
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141210-150832641
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52565
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:11 Dec 2014 17:07
Last Modified:30 Nov 2017 22:27

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