State space c-reductions for concurrent systems in rewriting logic

We present c-reductions, a state space reduction technique. The rough idea is to exploit some equivalence relation on states (possibly capturing system regularities) that preserves behavioral properties, and explore the induced quotient system. This is done by means of a canonizer function, which maps each state into a (non necessarily unique) canonical representative of its equivalence class. The approach exploits the expressiveness of rewriting logic and its realization in Maude to enjoy several advantages over similar approaches: exibility and simplicity in the definition of the reductions (supporting not only traditional symmetry reductions, but also name reuse and name abstraction); reasoning support for checking and proving correctness of the reductions; and automatization of the reduction infrastructure via Maude's meta-programming features. The approach has been validated over a set of representative case studies, exhibiting comparable results with respect to other tools

Modeling Variable Emission Lines in AGNs: Method and Application to NGC 5548

We present a new scheme for modeling the broad line region in active galactic nuclei (AGNs). It involves photoionization calculations of a large number of clouds, in several pre-determined geometries, and a comparison of the calculated line intensities with observed emission line light curves. Fitting several observed light curves simultaneously provides strong constraints on model parameters such as the run of density and column density across the nucleus, the shape of the ionizing continuum, and the radial distribution of the emission line clouds. When applying the model to the Seyfert 1 galaxy NGC 5548, we were able to reconstruct the light curves of four ultraviolet emission-lines, in time and in absolute flux. This has not been achieved by any previous work. We argue that the Balmer lines light curves, and possibly also the MgII2798 light curve, cannot be tested in this scheme because of the limitations of present-day photoionization codes. Our fit procedure can be used to rule out models where the particle density scales as r^{-2}, where r is the distance from the central source. The best models are those where the density scales as r^{-1} or r^{-1.5}. We can place a lower limit on the column density at a distance of 1 ld, of N_{col}(r=1) >~ 10^{23} cm^{-2} and limit the particle density to be in the range of 10^{12.5}>N(r=1)>10^{11} cm^{-3}. We have also tested the idea that the spectral energy distribution (SED) of the ionizing continuum is changing with continuum luminosity. None of the variable-shape SED tried resulted in real improvement over a constant SED case although models with harder continuum during phases of higher luminosity seem to fit better the observed spectrum. Reddening and/or different composition seem to play a minor role, at least to the extent tested in this work.Comment: 12 pages, including 9 embedded EPS figures, accepted for publication in Ap

Spitzer/IRS Observations of Seyfert 1.8s and 1.9s: A Comparison with Seyfert 1s and Seyfert 2s

We present Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8 and 1.9 galaxies over the 5-38 um region. We compare the spectral characteristics of this sample to those of 58 Seyfert 1 and Seyfert 2 galaxies from the Spitzer archives. An analysis of the spectral shapes, the silicate 10 um feature and the emission line fluxes have enabled us to characterize the mid-IR properties of Seyfert 1.8/1.9s. We find that the equivalent widths of the 10 um silicate feature are generally weak in all Seyfert galaxies, as previously reported by several studies. The few Seyfert galaxies in this sample that show deep 10 um silicate absorption features are highly inclined and/or merging galaxies. It is likely that these absorption features originate primarily in the dusty interstellar medium of the host galaxy rather than in a dusty torus on parsec scales close to the central engine. We find that the equivalent width of the polycyclic aromatic hydrocarbon (PAH) band at 6.2 um correlates strongly with the 20-30 um spectral index. Either of these quantities are good indicators of the amount of starburst contribution to the mid-IR spectra. The spectra of Seyfert 1.8 and 1.9s are dominated by these starburst features, similar to most Seyfert 2s. They show strong PAH bands and a strong red continuum toward 30 um. The strengths of the high-ionization forbidden narrow emission lines [O IV] 25.89 um, [Ne III] 15.56 um and [Ne V] 14.32 um relative to [Ne II] 12.81 um are weaker in Seyfert 1.8/1.9s and Seyfert 2s as compared to Seyfert 1s. The weakness of high-ionization lines in Seyfert 1.8-1.9s is suggestive of intrinsically weak active galactic nuclei (AGN) continua, and/or stronger star formation activity leading to enhanced [Ne II]. We discuss the implications of these observational results in the context of the Unified Model of AGN.Comment: 36 pages, 4 tables, 6 figures, Accepted for publication in The Astrophysical Journal, December 200

Tactics for Reasoning modulo AC in Coq

We present a set of tools for rewriting modulo associativity and commutativity (AC) in Coq, solving a long-standing practical problem. We use two building blocks: first, an extensible reflexive decision procedure for equality modulo AC; second, an OCaml plug-in for pattern matching modulo AC. We handle associative only operations, neutral elements, uninterpreted function symbols, and user-defined equivalence relations. By relying on type-classes for the reification phase, we can infer these properties automatically, so that end-users do not need to specify which operation is A or AC, or which constant is a neutral element.Comment: 16

NuSTAR + XMM-Newton monitoring of the neutron star transient AX J1745.6-2901

AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star (NS) Low Mass X-ray Binary (LMXB) showcasing intense ionised Fe K absorption. We present here the analysis of 11 XMM-Newton and 15 NuSTAR new data-sets (obtained between 2013-2016), therefore tripling the number of observations of AX J1745.6-2901 in outburst. Thanks to simultaneous XMM-Newton and NuSTAR spectra, we greatly improve on the fitting of the X-ray continuum. During the soft state the emission can be described by a disk black body ($kT\sim1.1-1.2$ keV and inner disc radius $r_{DBB}\sim14$ km), plus hot ($kT\sim2.2-3.0$ keV) black body radiation with a small emitting radius ($r_{BB}\sim0.5-0.8$ km) likely associated with the boundary layer or NS surface, plus a faint Comptonisation component. Imprinted on the spectra are clear absorption features created by both neutral and ionised matter. Additionally, positive residuals suggestive of an emission Fe K$\alpha$ disc line and consistent with relativistic ionised reflection are present during the soft state, while such residuals are not significant during the hard state. The hard state spectra are characterised by a hard ($\Gamma\sim1.9-2.1$) power law, showing no evidence for a high energy cut off ($kT_e>60-140$ keV) and implying a small optical depth ($\tau<1.6$). The new observations confirm the previously witnessed trend of exhibiting strong Fe K absorption in the soft state, that significantly weakens during the hard state. Optical (GROND) and radio (GMRT) observations suggest for AX J1745.6-2901 a standard broad band SED as typically observed in accreting neutron stars.Comment: Accepted for publication in MNRA

Reddening, Emission-Line, and Intrinsic Absorption Properties in the Narrow-Line Seyfert 1 Galaxy Akn 564

We use Hubble Space Telescope UV and optical spectra of the narrow-line Seyfert 1 (NLS1) galaxy Akn 564 to investigate its internal reddening and properties of its emission-line and intrinsic UV absorption gas. We find that the extinction curve of Akn 564, derived from a comparison of its UV/optical continuum to that of an unreddened NLS1, lacks a 2200 A bump and turns up towards the UV at a longer wavelength (4000 A) than the standard Galactic, LMC, and SMC curves. However, it does not show the extremely steep rise to 1200 A that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The emission-lines and continuum experience the same amount of reddening, indicating the presence of a dust screen that is external to the narrow-line region (NLR). Echelle spectra from the Space Telescope Imaging Spectrograph show intrinsic UV absorption lines due to Ly-alpha, N V, C IV, Si IV, and Si III, centered at a radial velocity of -190 km/s (relative to the host galaxy). Photoionization models of the UV absorber indicate that it has a sufficient columnand is at a sufficient distance from the nucleus (D > 95 pc) to be the source of the dust screen. Thus, Akn 564 contains a dusty ``lukewarm absorber'' similar to that seen in NGC 3227.Comment: 25 pages, 4 figures. LaTeX with encapsulated postscript figures. Accepted for publication in the Astrophysical Journa

Neighborhood Racial Discrimination and the Development of Major Depression

This study examined the impact of neighborhood racial discrimination on the development of major depressive disorder (MDD) in a sample of African American women. Participants were 499 women from Georgia and Iowa with no history of MDD who were followed for 9 to 11 years. Several neighborhood characteristics (community social disorder, community cohesion, and community racism) and individual characteristics (negative life events, financial strain, personal outlook, religious involvement, relationship quality, negative affectivity, and individual experiences of racism) were employed as predictors of whether or not the women met criteria for MDD during this period of time. In a multilevel logistic regression analysis, neighborhood-level discrimination as well as individual-level variables including the number of negative life events, financial strain, and negative affectivity were found to be significant predictors of developing MDD. Analyses of cross-level interactions indicated that the effects of neighborhood-level discrimination were moderated by the quality of individuals’ relationships, such that better relationships with others served to lessen the effect of neighborhood discrimination on depression. Implications of these findings for understanding the negative effects of racial discrimination are discussed

The Extraordinary Mid-infrared Spectrum of the Blue Compact Dwarf Galaxy SBS0335-052

SBS0335-052 is a blue compact dwarf galaxy (BCD) with one of the lowest known metallicities, Z$\sim$Z_{\sun}/41, making it a local example of how primordial starburst galaxies and their precursors might appear. A spectrum obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope clearly shows silicate absorption features, emission lines of [SIV] and [NeIII], and puts strong upper limits on the PAH emission features. The observed low resolution spectrum (R~90) extends from 5.3 to 35microns and peaks at ~28microns. The spectrum is compared to IRS observations of the prototypical starburst nucleus NGC7714. SBS0335-052 is quite unlike normal starburst galaxies, which show strong PAH bands, low ionization emission lines, and a continuum peak near 80microns. The continuum difference for $\lambda >30 \mu$m implies a substantial reduction in the mass of cold dust. If the spectrum of this very low metallicity galaxy is representative of star forming galaxies at higher redshifts, it may be difficult to distinguish them from AGNs which also show relatively featureless flat spectra in the mid-IR.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 2 figure