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Title: NUSTAR AND XMM-NEWTON OBSERVATIONS OF THE EXTREME ULTRALUMINOUS X-RAY SOURCE NGC 5907 ULX1: A VANISHING ACT

We present results obtained from two broadband X-ray observations of the extreme ultraluminous X-ray source (ULX) NGC 5907 ULX1, known to have a peak X-ray luminosity of ∼5 × 10{sup 40} erg s{sup –1}. These XMM-Newton and NuSTAR observations, separated by only ∼4 days, revealed an extreme level of short-term flux variability. In the first epoch, NGC 5907 ULX1 was undetected by NuSTAR, and only weakly detected (if at all) with XMM-Newton, while in the second NGC 5907 ULX1 was clearly detected at high luminosity by both missions. This implies an increase in flux of ∼2 orders of magnitude or more during this ∼4 day window. We argue that this is likely due to a rapid rise in the mass accretion rate, rather than to a transition from an extremely obscured to an unobscured state. During the second epoch we observed the broadband 0.3-20.0 keV X-ray luminosity to be (1.55 ± 0.06) × 10{sup 40} erg s{sup –1}, similar to the majority of the archival X-ray observations. The broadband X-ray spectrum obtained from the second epoch is inconsistent with the low/hard accretion state observed in Galactic black hole binaries, but is well modeled with a simple accretion disk model incorporating the effects of photon advection.more » This strongly suggests that when bright, NGC 5907 ULX1 is a high-Eddington accretor.« less
Authors:
;  [1] ; ; ; ; ;  [2] ; ; ;  [3] ; ;  [4] ;  [5] ;  [6] ;  [7] ; ;  [8] ;  [9]
  1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
  2. Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States)
  3. Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France)
  4. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
  5. DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
  6. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
  7. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  8. Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)
  9. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
Publication Date:
OSTI Identifier:
22364410
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 799; 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; ADVECTION; BLACK HOLES; COSMIC PHOTONS; COSMIC X-RAY SOURCES; GALAXY CLUSTERS; KEV RANGE; LUMINOSITY; STAR CLUSTERS; X RADIATION; X-RAY SPECTRA