BL Lac evolution revisited

BL Lac objects are an elusive and rare class of active galactic nuclei. For years their evolutionary behavior has appeared inconsistent with the trend observed in the population of AGN at large. The so-called ``negative'' evolution implies that BL Lacs were either less or fainter in the past. This effect is stronger for BL Lacs selected in X-ray surveys. We have investigated if one of the selection criteria, namely the flat-radio spectrum (imposed on the Radio-selected but not on the X-ray-selected samples), might explain the different evolutionary trend.Comment: Proceedings of "Multiwavelength AGN Surveys", Cozumel, Dec 200

Radio spectra of a sample of X-ray selected BL Lacs

We present simultaneous multifrequency radio observations for a complete subsample of 26 XBLs from the Einstein Extended Medium-Sensitivity Survey, obtained with the Very Large Array (VLA). Spectra are computed using fluxes at 20, 6 and 3.6 cm. Unlike many radio selected samples, the EMSS did not impose any criterion on the radio spectrum to identify BL Lac objects. It is therefore possible to investigate the intrinsic radio spectral slope distribution and to determine the effect produced by this selection criterion. We find that 15% of the observed objects do not meet the flat-spectrum criterion imposed on some other BL Lac samples. A dataset that includes non-simultaneous data (that are also taken with different VLA configurations) shows an even higher percentage of steep spectrum sources. This effect can be ascribed to a larger fraction of extended flux detected with the more compact VLA configuration.Possible biases introduced by the flat--radio-spectrum criterion in the radio-selected BL Lac samples cannot explain the discrepancies observed in the evolutionary properties of Radio and X-ray selected samples of BL Lacs.Comment: 9 pages, 5 figures, to be published in Astronomy and Astrophysic

Broadening the Scope of Nanopublications

In this paper, we present an approach for extending the existing concept of nanopublications --- tiny entities of scientific results in RDF representation --- to broaden their application range. The proposed extension uses English sentences to represent informal and underspecified scientific claims. These sentences follow a syntactic and semantic scheme that we call AIDA (Atomic, Independent, Declarative, Absolute), which provides a uniform and succinct representation of scientific assertions. Such AIDA nanopublications are compatible with the existing nanopublication concept and enjoy most of its advantages such as information sharing, interlinking of scientific findings, and detailed attribution, while being more flexible and applicable to a much wider range of scientific results. We show that users are able to create AIDA sentences for given scientific results quickly and at high quality, and that it is feasible to automatically extract and interlink AIDA nanopublications from existing unstructured data sources. To demonstrate our approach, a web-based interface is introduced, which also exemplifies the use of nanopublications for non-scientific content, including meta-nanopublications that describe other nanopublications.Comment: To appear in the Proceedings of the 10th Extended Semantic Web Conference (ESWC 2013

X-Ray Spectral Variability of PKS 2005-489 During the Spectacular November 1998 Flare

We report on monitoring of the BL Lac object PKS 2005-489 by the Rossi X-ray Timing Explorer (RXTE) in October-December 1998. During these months, the source underwent a spectacular flare; at its peak on November 10, its 2-10 keV flux was $3.33 \times 10^{-10} {\rm ~erg ~cm^{-2} ~s^{-1}}$, over 30 times brighter than in quiescence. During the rising phase, the X-ray spectrum of PKS 2005-489 hardened considerably, reaching $\alpha = 1.32~ (F_\nu \propto \nu^{-\alpha})$ near maximum. During the declining phase, the X-ray spectrum steepened rapidly, reaching $\alpha = 1.82$, then became somewhat harder towards the end of December ($\alpha \sim 1.6$). While such behavior has been seen before, the simplicity, magnitude and duration of this flare allowed us to study it in great detail. We argue that this flare was caused by either the injection of particles into the jet or {\it in situ} particle acceleration, and that the spectral steepening which followed the flare maximum was the result of synchrotron cooling. Contrary to other recently observed blazar flares (e.g., Mkn 501, 3C 279, PKS 2155-304), our results do not imply a major shift in the location of the synchrotron peak during this flare.Comment: ApJ Letters in press, 6 pages, 2 figures Corrected reference

"Dark Matter" in Accretion Disks

Using Spitzer Space Telescope photometric observations of the eclipsing, interacting binary WZ Sge, we have discovered that the accretion disk is far more complex than previously believed. Our 4.5 and 8 micron time series observations reveal that the well known gaseous accretion disk is surrounded by an asymmetric disk of dusty material with a radius approximately 15 times larger than the gaseous disk. This dust ring contains only a small amount of mass and is completely invisible at optical and near-IR wavelengths, hence consisting of "dark matter". We have produced a model dust ring using 1 micron spherical particles with a density of 3 g/cm$^3$ and with a temperature profile ranging from 700-1500K. Our discovery about the accretion disk structure and the presence of a larger, outer dust ring have great relevance for accretion disks in general, including those in other interacting binary systems, pre-main sequence stars, and active galaxies.Comment: 34 pages, 8 figures (3 in color). Accepted to Ap

Variational Geometric Approach To Generalized Differential And Conjugate Calculi In Convex Analysis

This paper develops a geometric approach of variational analysis for the case of convex objects considered in locally convex topological spaces and also in Banach space settings. Besides deriving in this way new results of convex calculus, we present an overview of some known achievements with their unified and simplified proofs based on the developed geometric variational schemes. Key words. Convex and variational analysis, Fenchel conjugates, normals and subgradients, coderivatives, convex calculus, optimal value functions