Constraining Emission Models of Luminous Blazar Sources

Many luminous blazars which are associated with quasar-type active galactic nuclei display broad-band spectra characterized by a large luminosity ratio of their high-energy (gamma-ray) and low-energy (synchrotron) spectral components. This large ratio, reaching values up to 100, challenges the standard synchrotron self-Compton models by means of substantial departures from the minimum power condition. Luminous blazars have also typically very hard X-ray spectra, and those in turn seem to challenge hadronic scenarios for the high energy blazar emission. As shown in this paper, no such problems are faced by the models which involve Comptonization of radiation provided by a broad line-region, or dusty molecular torus. The lack or weakness of bulk Compton and Klein-Nishina features indicated by the presently available data favors production of gamma-rays via up-scattering of infrared photons from hot dust. This implies that the blazar emission zone is located at parsec-scale distances from the nucleus, and as such is possibly associated with the extended, quasi-stationary reconfinement shocks formed in relativistic outflows. This scenario predicts characteristic timescales for flux changes in luminous blazars to be days/weeks, consistent with the variability patterns observed in such systems at infrared, optical and gamma-ray frequencies. We also propose that the parsec-scale blazar activity can be occasionally accompanied by dissipative events taking place at sub-parsec distances and powered by internal shocks and/or reconnection of magnetic fields. These could account for the multiwavelength intra-day flares occasionally observed in powerful blazars sources.Comment: 34 pages, accepted for publication in the Astrophysical Journa

The low-frequency radio catalog of flat spectrum sources

A well known property of the gamma-ray sources detected by COS-B in the 1970s, by the Compton Gamma-ray Observatory in the 1990s and recently by the Fermi observations is the presence of radio counterparts, in particular for those associated to extragalactic objects. This observational evidence is the basis of the radio-gamma-ray connection established for the class of active galactic nuclei known as blazars. In particular, the main spectral property of the radio counterparts associated with gamma-ray blazars is that they show a flat spectrum in the GHz frequency range. Our recent analysis dedicated to search blazar-like candidates as potential counterparts for the unidentified gamma-ray sources (UGSs) allowed us to extend the radio-gamma-ray connection in the MHz regime. We also showed that below 1 GHz blazars maintain flat radio spectra. Thus on the basis of these new results, we assembled a low-frequency radio catalog of flat spectrum sources built by combining the radio observations of the Westerbork Northern Sky Survey (WENSS) and of the Westerbork in the southern hemisphere (WISH) catalog with those of the NRAO Very Large Array Sky survey (NVSS). This could be used in the future to search for new, unknown blazar-like counterparts of the gamma-ray sources. First we found NVSS counterparts of WSRT radio sources and then we selected flat spectrum radio sources according to a new spectral criterion specifically defined for radio observations performed below 1 GHz. We also described the main properties of the catalog listing 28358 radio sources and their logN-logS distributions. Finally a comparison with with the Green Bank 6-cm radio source catalog has been performed to investigate the spectral shape of the low-frequency flat spectrum radio sources at higher frequencies.Comment: 10 pages, 10 figures, 1 table, ApJS published in 2014 (pre-proof version uploaded

Doubly hybrid density functional for accurate descriptions of nonbond interactions, thermochemistry, and thermochemical kinetics

We develop and validate a density functional, XYG3, based on the adiabatic connection formalism and the Görling–Levy coupling-constant perturbation expansion to the second order (PT2). XYG3 is a doubly hybrid functional, containing 3 mixing parameters. It has a nonlocal orbital-dependent component in the exchange term (exact exchange) plus information about the unoccupied Kohn–Sham orbitals in the correlation part (PT2 double excitation). XYG3 is remarkably accurate for thermochemistry, reaction barrier heights, and nonbond interactions of main group molecules. In addition, the accuracy remains nearly constant with system size

What Can Gamma Ray Bursts Teach Us About Dark Energy?

It has been suggested that Gamma Ray Bursts (GRB) may enable the expansion rate of our Universe to be measured out to very high redshifts (z \gsim 5) just as type Ia supernovae have done at $z \sim$1--1.5. We explore this possibility here, and find that GRB have the potential to detect dark energy at high statistical significance, but they are unlikely to be competitive with future supernovae missions, such as SNAP, in measuring the properties of the dark energy. The exception to this conclusion is if there is appreciable dark energy at early times, in which case the information from GRB's will provide an excellent complement to the $z\sim 1$ information from supernovae.Comment: 5 pages, 9 figure

Spatial multi-criteria decision analysis to predict suitability for African swine fever endemicity in Africa

Background African swine fever (ASF) is endemic in several countries of Africa and may pose a risk to all pig producing areas on the continent. Official ASF reporting is often rare and there remains limited awareness of the continent-wide distribution of the disease. In the absence of accurate ASF outbreak data and few quantitative studies on the epidemiology of the disease in Africa, we used spatial multi-criteria decision analysis (MCDA) to derive predictions of the continental distribution of suitability for ASF persistence in domestic pig populations as part of sylvatic or domestic transmission cycles. In order to incorporate the uncertainty in the relative importance of different criteria in defining suitability, we modelled decisions within the MCDA framework using a stochastic approach. The predictive performance of suitability estimates was assessed via a partial ROC analysis using ASF outbreak data reported to the OIE since 2005. Results Outputs from the spatial MCDA indicate that large areas of sub-Saharan Africa may be suitable for ASF persistence as part of either domestic or sylvatic transmission cycles. Areas with high suitability for pig to pig transmission (‘domestic cycles’) were estimated to occur throughout sub-Saharan Africa, whilst areas with high suitability for introduction from wildlife reservoirs (‘sylvatic cycles’) were found predominantly in East, Central and Southern Africa. Based on average AUC ratios from the partial ROC analysis, the predictive ability of suitability estimates for domestic cycles alone was considerably higher than suitability estimates for sylvatic cycles alone, or domestic and sylvatic cycles in combination. Conclusions This study provides the first standardised estimates of the distribution of suitability for ASF transmission associated with domestic and sylvatic cycles in Africa. We provide further evidence for the utility of knowledge-driven risk mapping in animal health, particularly in data-sparse environments.</p

Can Cosmic Structure form without Dark Matter?

One of the prime pieces of evidence for dark matter is the observation of large overdense regions in the universe. Since we know from the cosmic microwave background that the regions that contained the most baryons when the universe was ~400,000 years old were overdense by only one part in ten thousand, perturbations had to have grown since then by a factor greater than $(1+z_*)\simeq 1180$ where $z_*$ is the epoch of recombination. This enhanced growth does not happen in general relativity, so dark matter is needed in the standard theory. We show here that enhanced growth can occur in alternatives to general relativity, in particular in Bekenstein's relativistic version of MOdified Newtonian Dynamics (MOND). The vector field introduced in that theory for a completely different reason plays a key role in generating the instability that produces large cosmic structures today.Comment: 5 pages, 3 figure

Kepler constraints on planets near hot Jupiters

We present the results of a search for planetary companions orbiting near hot Jupiter planet candidates (Jupiter-size candidates with orbital periods near 3 d) identified in the Kepler data through its sixth quarter of science operations. Special emphasis is given to companions between the 2∶1 interior and exterior mean-motion resonances. A photometric transit search excludes companions with sizes ranging from roughly two-thirds to five times the size of the Earth, depending upon the noise properties of the target star. A search for dynamically induced deviations from a constant period (transit timing variations) also shows no significant signals. In contrast, comparison studies of warm Jupiters (with slightly larger orbits) and hot Neptune-size candidates do exhibit signatures of additional companions with these same tests. These differences between hot Jupiters and other planetary systems denote a distinctly different formation or dynamical history

Human immunodeficiency virus rebound after suppression to < 400 copies/mL during initial highly active antiretroviral therapy regimens, according to prior nucleoside experience and duration of suppression

This study evaluated 1433 human immunodeficiency virus (HIV)-infected patients starting highly active antiretroviral therapy (HAART), 409 (28%) of whom had prior nucleoside experience and achieved an HIV load of <400 copies/mL by 24 weeks of therapy. Three hundred seven patients experienced virus rebound during a total of 2773.3 person-years of follow-up. There was a higher rate of virus rebound among the patients with pre-HAART nucleoside experience (relative hazard [RH], 2.86; 95% confidence interval, 2.22-3.84; P < .0001) and a decreasing rate of virus rebound with increasing duration of virus suppression (i.e., time since achieving a virus load of <400 HIV RNA copies/mL) among both the nucleoside-experienced and naive patients (P < .0001), but the difference between the groups persisted into the third year of follow-up (P = .0007). Even patients who had experienced <2 months of nucleoside therapy before beginning HAART had an increased risk of virus rebound (RH, 1.95; P = .009). It appears that only a small period of pre-HAART nucleoside therapy is sufficient to confer a disadvantage, in terms of risk of virus rebound, that persists for several years

Harnessing optical micro-combs for microwave photonics

In the past decade, optical frequency combs generated by high-Q micro-resonators, or micro-combs, which feature compact device footprints, high energy efficiency, and high-repetition-rates in broad optical bandwidths, have led to a revolution in a wide range of fields including metrology, mode-locked lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum optics. Among these, an application that has attracted great interest is the use of micro-combs for RF photonics, where they offer enhanced functionalities as well as reduced size and power consumption over other approaches. This article reviews the recent advances in this emerging field. We provide an overview of the main achievements that have been obtained to date, and highlight the strong potential of micro-combs for RF photonics applications. We also discuss some of the open challenges and limitations that need to be met for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference

Optical spectroscopic observations of blazars and gamma-ray blazar candidates in the Sloan Digital Sky Survey Data Release Nine

We present an analysis of the optical spectra available in the Sloan Digital Sky survey data release nine (SDSS DR9) for the blazars listed in the ROMA-BZCAT and for the gamma-ray blazar candidates selected according to their IR colors. First, we adopt a statistical approach based on MonteCarlo simulations to find the optical counterparts of the blazarslisted in the ROMA-BZCAT catalog. Then we crossmatched the SDSS spectroscopic catalog with our selected samples of blazars and gamma-ray blazar candidates searching for those with optical spectra available to classify our blazar-like sources and, whenever possible, to confirm their redshifts. Our main objectives are determining the classification of uncertain blazars listed in the ROMA-BZCAT and discovering new gamma-ray blazars. For the ROMA-BZCAT sources we investigated a sample of 84 blazars confirming the classification for 20 of them and obtaining 18 new redshift estimates. For the gamma-ray blazars, indicated as potential counterparts of unassociated Fermi sources or with uncertain nature, we established the blazar-like nature of 8 out the 27 sources analyzed and confirmed 14 classifications.Comment: 7 pages, 2 figures, 4 tables, AJ published in 2014 (pre-proof version