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Title: The ultraluminous X-ray sources NGC 1313 X-1 and X-2: A broadband study with NuSTAR and XMM-Newton

We present the results of NuSTAR and XMM-Newton observations of the two ultraluminous X-ray sources: NGC 1313 X-1 and X-2. The combined spectral bandpass of the two satellites enables us to produce the first spectrum of X-1 between 0.3 and 30 keV, while X-2 is not significantly detected by NuSTAR above 10 keV. The NuSTAR data demonstrate that X-1 has a clear cutoff above 10 keV, whose presence was only marginally detectable with previous X-ray observations. This cutoff rules out the interpretation of X-1 as a black hole in a standard low/hard state, and it is deeper than predicted for the downturn of a broadened iron line in a reflection-dominated regime. The cutoff differs from the prediction of a single-temperature Comptonization model. Further, a cold disk-like blackbody component at ∼0.3 keV is required by the data, confirming previous measurements by XMM-Newton only. We observe a spectral transition in X-2, from a state with high luminosity and strong variability to a lower-luminosity state with no detectable variability, and we link this behavior to a transition from a super-Eddington to a sub-Eddington regime.
Authors:
; ;  [1] ; ; ; ; ; ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6] ; ; ;  [7] ;  [8] ;  [9]
  1. Université de Toulouse, UPS-OMP, IRAP, Toulouse (France)
  2. Cahill Center for Astronomy and Astrophysics, Caltech, Pasadena, CA 91125 (United States)
  3. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
  4. DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
  5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  6. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
  7. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  8. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States)
  9. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
Publication Date:
OSTI Identifier:
22341893
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; FORECASTING; IRON; KEV RANGE; LUMINOSITY; REFLECTION; SATELLITES; SPECTRA; STARS; X RADIATION; X-RAY SOURCES