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

作者：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

来源：Astrophysical Journal, 2015, 799(2): 122.

DOI：10.1088/0004-637X/799/2/122

• black hole physics
• X-rays: binaries
• X-rays: individual (NGC 5907 ULX1)

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 similar to 5 x 10(40) erg s(-1). These XMM-Newton and NuSTAR observations, separated by only similar to 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 similar to 2 orders of magnitude or more during this similar to 4 day 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) x 10(40) 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.

• 出版日期2015-2-1