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http://hdl.handle.net/20.500.12386/24003
Titolo: | NuSTAR and XMM-Newton Observations of the Extreme Ultraluminous X-Ray Source NGC 5907 ULX1: A Vanishing Act | Autori: | Walton, D. J. Harrison, F. A. BACHETTI, Matteo Barret, D. Boggs, S. E. Christensen, F. E. Craig, W. W. Fuerst, F. Grefenstette, B. W. Hailey, C. J. Madsen, K. K. Middleton, M. J. Rana, V. Roberts, T. P. Stern, D. Sutton, A. D. Webb, N. Zhang, W. |
Data pubblicazione: | 2015 | Rivista: | THE ASTROPHYSICAL JOURNAL | Numero: | 799 | Fascicolo: | 2 | Da pagina:: | 122 | Abstract: | 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</SUP> erg s<SUP>-1</SUP>. 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</SUP> erg s<SUP>-1</SUP>, 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. This strongly suggests that when bright, NGC 5907 ULX1 is a high-Eddington accretor. | Acknowledgments: | The authors would like to thank the reviewer for positive and useful feedback, which helped improve the manuscript, as well as Diego Altamarino for useful discussions. M.B. and D.B. acknowledge financial support from the French Space Agency (CNES). 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, and has utilized the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and Caltech (USA). This research has also made use of data obtained with XMM-Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, and NASA's Chandra and Swift satellites. Facilites: NuSTAR , XMM , Chandra , Swift | URI: | http://hdl.handle.net/20.500.12386/24003 | URL: | https://iopscience.iop.org/article/10.1088/0004-637X/799/2/122 | ISSN: | 0004-637X | DOI: | 10.1088/0004-637X/799/2/122 | Bibcode ADS: | 2015ApJ...799..122W | Fulltext: | open |
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