Inhomogeneous accretion discs and the soft states of black hole X-ray binaries

Observations of black hole binaries (BHBs) have established a rich phenomenology of X-ray states. The soft states range from the low variability, accretion disc dominated thermal state (TD) to the higher variability, non-thermal steep power law state (SPL). The disc component in all states is typically modeled with standard thin disc accretion theory. However, this theory is inconsistent with optical/UV spectral, variability, and gravitational microlensing observations of active galactic nuclei (AGNs), the supermassive analogs of BHBs. An inhomogeneous disc (ID) model with large (~0.4 dex) temperature fluctuations in each radial annulus can qualitatively explain all of these AGN observations. The inhomogeneity may be a consequence of instabilities in radiation dominated discs, and therefore may be present in BHBs as well. We show that ID models can explain many features of the TD and SPL states of BHBs. The observed relationships between spectral hardness, disc fraction, and rms variability amplitude in BHBs are reproduced with temperature fluctuations similar to those inferred in AGNs, suggesting a unified picture of luminous accretion discs across orders of magnitude in black hole mass. This picture can be tested with spectral fitting of ID models, X-ray polarization observations, and radiation MHD simulations. If BHB accretion discs are indeed inhomogeneous, only the most disc dominated states (disc fraction > 0.95) can be used to robustly infer black hole spin using current continuum fitting methods.Comment: 5 pages, 3 figures, submitted to MNRAS Letter

Peer Victimization, Internalizing Problems, and Substance Use in Urban African American Adolescents in Chicago: The Relevance of the Self-Medication Hypothesis

The aim of the study was to explore the link between peer victimization and substance use and tested the mediating role of internalizing problems in urban African American adolescents in Chicago. Six hundred and thirty-eight adolescents in Chicago\u27s Southside participated in the study. Results from the hierarchical linear regression analysis showed that youth who reported peer victimization were at risk of internalizing problems. Those who were bullied by their peers were more likely to display internalizing problems, which was also significantly associated with substance use. Consistent with the self-medication hypothesis, findings from the study suggest that bullied youth are likely to display internalizing problems and turn to substance use. Implications for mental health practice in school settings are also discussed

The Optical, Ultraviolet, and X-ray Structure of the Quasar HE 0435-1223

Microlensing has proven an effective probe of the structure of the innermost regions of quasars, and an important test of accretion disk models. We present light curves of the lensed quasar HE 0435-1223 in the R band and in the ultraviolet, and consider them together with X-ray light curves in two energy bands that are presented in a companion paper. Using a Bayesian Monte Carlo method, we constrain the size of the accretion disk in the rest-frame near- and far-UV, and constrain for the first time the size of the X-ray emission regions in two X-ray energy bands. The R-band scale size of the accretion disk is about 10^15.23 cm (~23 r_g), slightly smaller than previous estimates, but larger than would be predicted from the quasar flux. In the UV, the source size is weakly constrained, with a strong prior dependence. The UV to R-band size ratio is consistent with the thin disk model prediction, with large error bars. In soft and hard X-rays, the source size is smaller than ~10^14.8 cm (~10 r_g) at 95% confidence. We do not find evidence of structure in the X-ray emission region, as the most likely value for the ratio of the hard X-ray size to the soft X-ray size is unity. Finally, we find that the most likely value for the mean mass of stars in the lens galaxy is ~0.3 M_sun, consistent with other studies.Comment: 13 pages, 7 figures. Replaced with version accepted to Ap

A Description of Quasar Variability Measured Using Repeated SDSS and POSS Imaging

We provide a quantitative description and statistical interpretation of the optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS) has obtained repeated imaging in five UV-to-IR photometric bands for 33,881 spectroscopically confirmed quasars. About 10,000 quasars have an average of 60 observations in each band obtained over a decade along Stripe 82 (S82), whereas the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed time lags span the range from a day to almost 10 years, and constrain quasar variability at rest-frame time lags of up to 4 years, and at rest-frame wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of quasars from the SDSS Data Release 7 that have been observed at least twice in SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it to analyze the ensemble properties of quasar variability. Based on a damped random walk (DRW) model defined by a characteristic time scale and an asymptotic variability amplitude that scale with the luminosity, black hole mass, and rest wavelength for individual quasars calibrated in S82, we can fully explain the ensemble variability statistics of the non-S82 quasars such as the exponential distribution of large magnitude changes. All available data are consistent with the DRW model as a viable description of the optical continuum variability of quasars on time scales of ~5-2000 days in the rest frame. We use these models to predict the incidence of quasar contamination in transient surveys such as those from PTF and LSST.Comment: 33 pages, 19 figures, replaced with accepted version. Catalog is available at http://www.astro.washington.edu/users/ivezic/macleod/qso_dr7

Out of the Orient: Post-Tethyan transoceanic and trans-Arabian routes fostered the spread of Baorini skippers in the Afrotropics

The origin of taxa presenting a disjunct distribution between Africa and Asia has puzzled biogeographers for more than a century. This biogeographic pattern has been hypothesized to be the result of transoceanic long-distance dispersal, Oligocene dispersal through forested corridors, Miocene dispersal through the Arabian Peninsula or passive dispersal on the rifting Indian plate. However, it has often been difficult to pinpoint the mechanisms at play. We investigate biotic exchange between the Afrotropics and the Oriental region during the Cenozoic, a period in which geological changes altered landmass connectivity. We use Baorini skippers (Lepidoptera, Hesperiidae) as a model, a widespread clade of butterflies in the Old World tropics with a disjunct distribution between the Afrotropics and the Oriental region. We use anchored phylogenomics to infer a robust evolutionary tree for Baorini skippers and estimate divergence times and ancestral ranges to test biogeographic hypotheses. Our phylogenomic tree recovers strongly supported relationships for Baorini skippers and clarifies the systematics of the tribe. Dating analyses suggest that these butterflies originated in the Oriental region, Greater Sunda Islands, and the Philippines in the early Miocene c. 23 Ma. Baorini skippers dispersed from the Oriental region towards Africa at least five times in the past 20 Ma. These butterflies colonized the Afrotropics primarily through trans-Arabian geodispersal after the closure of the Tethyan seaway in the mid-Miocene. Range expansion from the Oriental region towards the African continent probably occurred via the Gomphotherium land bridge through the Arabian Peninsula. Alternative scenarios invoking long-distance dispersal and vicariance are not supported. The Miocene climate change and biome shift from forested areas to grasslands possibly facilitated geodispersal in this clade of butterflies.Directorate for Biological Sciences. Grant Numbers: DEB‐1541500, DEB‐1541560.Peer reviewe

Phylogenetic Structure of Foliar Spectral Traits in Tropical Forest Canopies

The Spectranomics approach to tropical forest remote sensing has established a link between foliar reflectance spectra and the phylogenetic composition of tropical canopy tree communities vis-à-vis the taxonomic organization of biochemical trait variation. However, a direct relationship between phylogenetic affiliation and foliar reflectance spectra of species has not been established. We sought to develop this relationship by quantifying the extent to which underlying patterns of phylogenetic structure drive interspecific variation among foliar reflectance spectra within three Neotropical canopy tree communities with varying levels of soil fertility. We interpreted the resulting spectral patterns of phylogenetic signal in the context of foliar biochemical traits that may contribute to the spectral-phylogenetic link. We utilized a multi-model ensemble to elucidate trait-spectral relationships, and quantified phylogenetic signal for spectral wavelengths and traits using Pagel’s lambda statistic. Foliar reflectance spectra showed evidence of phylogenetic influence primarily within the visible and shortwave infrared spectral regions. These regions were also selected by the multi-model ensemble as those most important to the quantitative prediction of several foliar biochemical traits. Patterns of phylogenetic organization of spectra and traits varied across sites and with soil fertility, indicative of the complex interactions between the environmental and phylogenetic controls underlying patterns of biodiversity

Technical Consultation of the International Space Station (ISS) Internal Active Thermal Control System (IATCS) Cooling Water Chemistry

The Internal Active Thermal Control System (IATCS) coolant exhibited unexpected chemical changes during the first year of on-orbit operation following the launch and activation in February 2001. The coolant pH dropped from 9.3 to below the minimum specification limit of 9.0, and re-equilibrated between 8.3 and 8.5. This drop in coolant pH was shown to be the result of permeation of CO2 from the cabin into the coolant via Teflon flexible hoses which created carbonic acid in the fluid. This unexpected diffusion was the result of having a cabin CO2 partial pressure higher than the ground partial pressure (average 4.0 mmHg vs. less than 0.2 mmHg). This drop in pH was followed by a concurrent increasing coolant nickel concentration. No other metal ions were observed in the coolant and based on previous tests, the source of nickel ion was thought to be the boron nickel (BNi) braze intermetallics used in the construction of HXs and cold plates. Specifically, BNi2 braze alloy was used for the IATCS IFHX and BNi3 braze alloy was used for the IATCS Airlock Servicing and Performance Checkout Unit (SPCU) HX and cold plates. Given the failure criticality of the HXs, a Corrosion Team was established by the IATCS CWG to determine the impact of the nickel corrosion on hardware performance life

The Sloan Digital Sky Survey Reverberation Mapping Project: Rapid CIV Broad Absorption Line Variability

We report the discovery of rapid variations of a high-velocity CIV broad absorption line trough in the quasar SDSS J141007.74+541203.3. This object was intensively observed in 2014 as a part of the Sloan Digital Sky Survey Reverberation Mapping Project, during which 32 epochs of spectroscopy were obtained with the Baryon Oscillation Spectroscopic Survey spectrograph. We observe significant (>4sigma) variability in the equivalent width of the broad (~4000 km/s wide) CIV trough on rest-frame timescales as short as 1.20 days (~29 hours), the shortest broad absorption line variability timescale yet reported. The equivalent width varied by ~10% on these short timescales, and by about a factor of two over the duration of the campaign. We evaluate several potential causes of the variability, concluding that the most likely cause is a rapid response to changes in the incident ionizing continuum. If the outflow is at a radius where the recombination rate is higher than the ionization rate, the timescale of variability places a lower limit on the density of the absorbing gas of n_e > 3.9 x 10^5 cm^-3. The broad absorption line variability characteristics of this quasar are consistent with those observed in previous studies of quasars, indicating that such short-term variability may in fact be common and thus can be used to learn about outflow characteristics and contributions to quasar/host-galaxy feedback scenarios.Comment: 15 pages, 14 figures. Accepted for publication in the Astrophysical Journa