NuSTAR and XMM-Newton observations of the extreme ultraluminous X-ray source NGC 5907 ULX1 : a vanishing act
Walton, D.J.; Harrison, F.A.; Bachetti, M.; 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.
Professor Tim Roberts firstname.lastname@example.org
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.
Walton, D., Harrison, F., Bachetti, M., Barret, D., Boggs, S., Christensen, F., …Zhang, W. (2015). NuSTAR and XMM-Newton observations of the extreme ultraluminous X-ray source NGC 5907 ULX1 : a vanishing act. Astrophysical Journal, 799(2), Article 122. https://doi.org/10.1088/0004-637x/799/2/122
|Journal Article Type||Article|
|Publication Date||Feb 1, 2015|
|Deposit Date||Jan 30, 2015|
|Publicly Available Date||Feb 16, 2015|
|Publisher||American Astronomical Society|
|Peer Reviewed||Peer Reviewed|
|Keywords||Black hole physics, X-rays: binaries, X-rays: individual (NGC 5907 ULX1).|
|Related Public URLs||http://arxiv.org/abs/1411.5974|
Published Journal Article
© 2015. The American Astronomical Society. All rights reserved.
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