Caught in the act: Measuring the changes in the corona that cause the extreme variability of 1H 0707-495

The X-ray spectra of the narrow line Seyfert 1 galaxy, 1H 0707-495, obtained with XMM-Newton, from time periods of varying X-ray luminosity are analysed in the context of understanding the changes to the X-ray emitting corona that lead to the extreme variability seen in the X-ray emission from active galactic nuclei (AGN). The emissivity profile of the accretion disc, illuminated by the X-ray emitting corona, along with previous measurements of reverberation time lags are used to infer the spatial extent of the X-ray source. By fitting a twice-broken power law emissivity profile to the relativistically-broadened iron K fluorescence line, it is inferred that the X-ray emitting corona expands radially, over the plane of the accretion disc, by 25 to 30 per cent as the luminosity increases, contracting again as the luminosity decreases, while increases in the measured reverberation lag as the luminosity increases would require also variation in the vertical extent of the source above the disc. The spectrum of the X-ray continuum is found to soften as the total X-ray luminosity increases and we explore the variation in reflected flux as a function of directly-observed continuum flux. These three observations combined with simple, first-principles models constructed from ray tracing simulations of extended coron self-consistently portray an expanding corona whose average energy density decreases, but with a greater number of scattering particles as the luminosity of this extreme object increases.Comment: 12 pages, 4 figures. Accepted for publication in MNRA

The curious time lags of PG 1244+026: Discovery of the iron K reverberation lag

High-frequency iron K reverberation lags, where the red wing of the line responds before the line centroid, are a robust signature of relativistic reflection off the inner accretion disc. In this letter, we report the discovery of the Fe K lag in PG 1244+026 from ~120 ks of data (1 orbit of the XMM-Newton telescope). The amplitude of the lag with respect to the continuum is 1000 s at a frequency of ~1e-4 Hz. We also find a possible frequency-dependence of the line: as we probe higher frequencies (i.e. shorter timescales from a smaller emitting region) the Fe K lag peaks at the red wing of the line, while at lower frequencies (from a larger emitting region) we see the dominant reflection lag from the rest frame line centroid. The mean energy spectrum shows a strong soft excess, though interestingly, there is no indication of a soft lag. Given that this source has radio emission and it has little reported correlated variability between the soft excess and the hard band, we explore one possible explanation in which the soft excess in this source is dominated by the steep power-law like emission from a jet, and that a corona (or base of the jet) irradiates the inner accretion disc, creating the blurred reflection features evident in the spectrum and the lag. General Relativistic ray-tracing models fit the Fe K lag well, with the best-fit giving a compact X-ray source at a height of 5 gravitational radii and a black hole mass of 1.3e7 Msun.Comment: 6 pages, 6 figures, resubmitted to MNRAS after moderate revisions. This paper focuses on the discovery of the Fe K reverberation lag in PG 1244+026. We point the interested reader to Alston, Done & Vaughan (See today: arXiv:submit/0851673), which focuses on the soft lags in this sourc

On how environmental stringency influences BMP adoption

Replaced with revised version of paper 06/22/06.Farm Management,

Identifying Characteristics Associated with Ileus Development Post Coronary Artery Bypass Graft Surgery

Background: Postoperative ileus (POI) is the period of intestinal paralysis following any surgical procedure. POI is manifested by nausea, vomiting, abdominal distention, delayed tolerance of oral diet and delayed time to flatus and stool. Little is known about POI following coronary artery bypass grafting (CABG) as no other study has focused specifically on the incidence of POI following CABG. Purpose: The primary objective of this study is to determine the incidence of POI post CABG. The secondary aim is to evaluate baseline characteristics associated with POI following CABG. Methods: This was a retrospective cohort study of 100 patients who underwent CABG from October 2014 to February 2015 at Nebraska Medicine. The incidence of POI was the primary outcome. Mann-Whitney U and Chi-square tests were used to compare characteristics between participants who did and did not develop POI. POI risk factors were determined using univariate logistic regression. Results: The incidence of POI was 15%. BMI and preoperative blood glucose were risk factors for POI (p=0.04 and p=0.03, respectively). Number of days until initiation of oral diet (p=0.014) and number of days until advancement to a solid diet (p=0.003) were also significant. Conclusion: POI is a significant complication in our population. Although further research is warranted, preoperative nutrition counseling may aid in reducing the incidence of POI by targeting weight loss and insulin sensitivity. Early postoperative oral diet may also be effective for reducing POI following CABG

Properties of AGN coronae in the NuSTAR era

The focussing optics of NuSTAR have enabled high signal-to-noise spectra to be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic Black Hole Binaries (BHB). Spectral modelling then allows robust characterization of the spectral index and upper energy cutoff of the coronal power-law continuum, after accounting for reflection and absorption effects. Spectral-timing studies, such as reverberation and broad iron line fitting, of these sources yield coronal sizes, often showing them to be small and in the range of 3 to 10 gravitational radii in size. Our results indicate that coronae are hot and radiatively compact, lying close to the boundary of the region in the compactness - temperature diagram which is forbidden due to runaway pair production. The coincidence suggests that pair production and annihilation are essential ingredients in the coronae of AGN and BHB and that they control the shape of the observed spectra.Comment: 11 pages, 8 figures, accepted for publication in MNRA