Ultraluminous X-ray sources

Ultraluminous X-ray sources (ULXs) are accreting black holes with X-ray luminosities in excess of the Eddington limit for a typical ~10 solar mass Galactic black hole. There is an emerging consensus that most ULXs are probably fairly typical stellar remnant black holes in a new super-Eddington `ultraluminous' accretion state, characterised by a soft excess and high energy spectral curvature, which may be associated with a radiatively-driven wind and cool, optically thick Comptonisation respectively. However, this scenario may be insufficient to produce some of the most luminous ULXs. Here we present a sample of extreme luminosity ULXs, and show that their X-ray spectral and timing properties are consistent with most of them being in the sub-Eddington low/hard state. Given their luminosities, this suggests that these ULXs contain 10^3-10^4 solar mass black holes. But, in one of the extreme ULXs we find evidence of high energy spectral curvature, which is a key feature of the ultraluminous state. We explore this ULX further, and show that its X-ray spectrum is consistent with being in the ultraluminous state, but with any wind emission obscured from view by the high column density of material in the direction of the source. We also investigate the ultraluminous state further, and present an X-ray spectral and timing study of ULXs with some of the highest quality XMM-Newton data. We show that their spectral and timing properties are consistent with current models of super-Eddington accretion, where a massive, radiatively-driven wind forms a funnel-like geometry around the source. Then, the observed X-ray properties are dependant on both the accretion rate, and the inclination at which the ULX system is observed. Finally, we consider optical counterparts to a small sample of ULXs. We fit the X-ray and optical data of these with a new spectral model of an irradiated, colour-temperature-corrected accretion disc, finding that ~0.1 per cent of their bolometric luminosity is reprocessed in the outer disc. This may be due to the opposing effects of self-shielding in the accretion disc and reflection in a super-Eddington wind

How I Got My Name

During the last days of slavery, my grandfather was a child on a plantation in Mississippi. He, being the son of a favorite household servant, was given the privilege of studying with the master\u27s children under an efficient tutor. Gratefulness for this opportunity and eagerness to learn caused him to advance rapidly

Timing in trace conditioning of the nictitating membrane response of the rabbit (Oryctolagus cuniculus) : scalar, nonscalar, and adaptive features

Using interstimulus intervals (ISIs) of 125, 250, and 500 msec in trace conditioning of the rabbit nictitating membrane response, the offset times and durations of conditioned responses (CRs) were collected along with onset and peak latencies. All measures were proportional to the ISI, but only onset and peak latencies conformed to the criterion for scalar timing. Regarding the CR’s possible protective overlap of the unconditioned stimulus (US), CR duration increased with ISI, while the peak’s alignment with the US declined. Implications for models of timing and CR adaptiveness are discussed

Eliminating Network Protocol Vulnerabilities Through Abstraction and Systems Language Design

Incorrect implementations of network protocol message specifications affect the stability, security, and cost of network system development. Most implementation defects fall into one of three categories of well defined message constraints. However, the general process of constructing network protocol stacks and systems does not capture these categorical con- straints. We introduce a systems programming language with new abstractions that capture these constraints. Safe and efficient implementations of standard message handling operations are synthesized by our compiler, and whole-program analysis is used to ensure constraints are never violated. We present language examples using the OpenFlow protocol