Please use this identifier to cite or link to this item:
|Title:||NuSTAR and XMM-Newton observations of the extreme ultraluminous X-ray source NGC 5907 ULX1: A Vanishing Act|
|Authors:||Walton, D. J.|
Harrison, F. A.
|Keywords:||black hole physics|
X-rays: individual: NGC 5907 ULX1
|Publisher:||IOP Sciences for The American Astronomical Society|
|Citation:||The Astrophysical Journal, 2015, Vol.799, p7|
|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 × 1040 erg s-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) × 1040 erg s-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. This strongly suggests that when bright, NGC 5907 ULX1 is a high-Eddington accretor.|
|Copyright:||2015, The American Astronomical Society|
|Appears in Collections:||Research Papers (A&A)|
Files in This Item:
|2015_ApJ_Vol.799_p122.pdf||Open Access||535.01 kB||Adobe PDF||View/Open|
Items in RRI Digital Repository are protected by copyright, with all rights reserved, unless otherwise indicated.