Discovery and Monitoring of a new Black Hole Candidate XTE J1752-223 with RXTE: RMS spectrum evolution, BH mass and the source distance

We report on the discovery and monitoring observations of a new galactic black hole candidate XTE J1752-223 by Rossi X-ray Timing Explorer (RXTE). The new source appeared on the X-ray sky on October 21 2009 and was active for almost 8 months. Phenomenologically, the source exhibited the low-hard/high-soft spectral state bi-modality and the variability evolution during the state transition that matches standard behavior expected from a stellar mass black hole binary. We model the energy spectrum throughout the outburst using a generic Comptonization model assuming that part of the input soft radiation in the form of a black body spectrum gets reprocessed in the Comptonizing medium. We follow the evolution of fractional root-mean-square (RMS) variability in the RXTE/PCA energy band with the source spectral state and conclude that broad band variability is strongly correlated with the source hardness (or Comptonized fraction). We follow changes in the energy distribution of rms variability during the low-hard state and the state transition and find further evidence that variable emission is strongly concentrated in the power-law spectral component. We discuss the implication of our results to the Comptonization regimes during different spectral states. Correlations of spectral and variability properties provide measurements of the BH mass and distance to the source. The spectral-timing correlation scaling technique applied to the RXTE observation during the hard-to-soft state transition indicates a mass of the BH in XTE J1752-223 between 8 and 11 solar masses and a distance to the source about 3.5 kiloparsec.Comment: Accepted for publication in The Astrophysical Journa

Disk and Coronal Instabilities in GRS 1915+105

We present time-resolved GRS 1915+105 energy and power spectra observed by RXTE, during an episode where the X-ray intensity makes an extreme dip. If the spectra are modeled in terms of disk and power law components, both have large variations. When the inner disk is disrupted, the power law dominates, exhibiting quasi-periodic oscillations with varying frequency until the inner disk returns.Comment: 4 pages, 1 figure,to be published in the proceedings of the conference "Accretion Processes in Astrophysics: Some Like it Hot", held at U. Md., October 1997, eds. S. Holt and T. Kallma

X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338

Since the discovery of the accreting millisecond pulsar XTE J1814-338 a total of 27 thermonuclear bursts have been observed from the source with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Spectroscopy of the bursts, as well as the presence of continuous burst oscillations, suggests that all but one of the bursts are sub-Eddington. The remaining burst has the largest peak bolometric flux of 2.64 x E^-8 erg/sec/cm^2, as well as a gap in the burst oscillations, similar to that seen in Eddington limited bursts from other sources. Assuming this burst was Eddington limited we obtain a source distance of about 8 kpc. All the bursts show coherent oscillations at the 314.4 Hz spin frequency. The burst oscillations are strongly frequency and phase locked to the persistent pulsations. Only two bursts show evidence for frequency drift in the first few seconds following burst onset. In both cases the initial drift corresponds to a spin down of a few tenths of a Hz. The large oscillation amplitude during the bursts confirms that the burst flux is modulated at the spin frequency. We detect, for the first time, a significant first harmonic component in burst oscillations. The ratio of countrate in the first harmonic to that in the fundamental can be > 0.25 and is, on average, less than that of the persistent pulsations. If the pulsations result from a single bright region on the surface, the harmonic strength suggests the burst emission is beamed, perhaps due to a stronger magnetic field than in non-pulsing LMXBs. Alternatively, the harmonic content could result from a geometry with two bright regions.Comment: AASTeX, 15 pages, 4 figures. Accepted for publication in the Astrophysical Journal Letter

Molecular Evolution of Hominoid Seminal Plasma Genes

When asking the question of what underlying genetic changes drive species to be different, it is debated whether protein coding or non-coding mutations are more important. The hominoids (humans, great apes, and gibbons) are a group of closely related species, yet vary widely in their mating system behaviors and predicted levels of sperm competition. In species where females mate with multiple males, sperm competition is hypothesized to increase the rate of adaptive evolution of proteins expressed in male reproductive tissues through recurrent selective sweeps (positive selection). Previous studies have shown this to be true for individual male reproductive genes. In a comprehensive study of over six hundred proteins expressed in ejaculated semen, however, the same trend was not observed. Although, parsing the data based on their different functional and expression properties identifies a subset of proteins that are likely targets for adaptive evolution driven by sexual selection. Two of these rapidly evolving proteins are the duplicated, primate specific semenogelins, SEMG1 and SEMG2. An in vitro expression system was used to test if selection was acting similarly on the non-coding regions, but no effect of mating system on the expression was observed. However, the two genes are expressed differently within each hominoid species. One model for divergence after gene duplication is duplication-divergence-complementation. This model was used in conjunction with phylogenetic footprinting to identify potential regulatory elements that may be important for expression level differences between the two genes

Space, Behavior, and Environmental Perception in Open Plan Offices: A Prospective Study

This prospective research study was conducted at a government office, which moved from an open plan office with somewhat enclosed workspaces to another open plan office with open workspaces. The study at the old office was conducted almost one year before the move, and the study at the new office was conducted more than one year after the move. The purpose of this study was threefold: (1) to measure and evaluate changes in patterns of accessibility and visibility due to changes in office layout, (2) to understand the effects of layout changes on observed behaviors, and (3) to determine the effects of layout changes on environmental perception. The study included the analysis of visibility and accessibility of each layout using space syntax techniques, field observations of behaviors, and questionnaire surveys of employees’ perception of privacy, job satisfaction and commitment to organization. During field observations, movement, visible copresence (i.e., the number of people visible from a space) and face-to-face interaction were observed along a predefined route in each office. Thirty-five people responded to the questionnaire survey at the old office. Out of 35, only 29 were available for survey at the new office. Based on the questionnaire survey data, three multi-item scales were constructed to measure perceived privacy, job satisfaction and commitment to organization. Results indicate better visibility and accessibility, increased face-to-face interactions, and improved perceived privacy at the new office. Results also show consistent effects of space on movement, and significant positive correlations between perceived privacy, job satisfaction and commitment to organization at these locations despite significant design differences. Implications of the research results and limitations of the research design are discussed