The subarcsecond mid-infrared view of local active galactic nuclei: II. The mid-infrared--X-ray correlation

We present an updated mid-infrared (MIR) versus X-ray correlation for the local active galactic nuclei (AGN) population based on the high angular resolution 12 and 18um continuum fluxes from the AGN subarcsecond MIR atlas and 2-10 keV and 14-195 keV data collected from the literature. We isolate a sample of 152 objects with reliable AGN nature and multi-epoch X-ray data and minimal MIR contribution from star formation. Although the sample is not homogeneous or complete, we show that our results are unlikely to be affected by biases. The MIR--X-ray correlation is nearly linear and within a factor of two independent of the AGN type and the wavebands used. The observed scatter is <0.4 dex. A possible flattening of the correlation slope at the highest luminosities probed (~ 10^45 erg/s) is indicated but not significant. Unobscured objects have, on average, an MIR--X-ray ratio that is only <= 0.15 dex higher than that of obscured objects. Objects with intermediate X-ray column densities (22 < log N_H < 23) actually show the highest MIR--X-ray ratio on average. Radio-loud objects show a higher mean MIR--X-ray ratio at low luminosities, while the ratio is lower than average at high luminosities. This may be explained by synchrotron emission from the jet contributing to the MIR at low-luminosities and additional X-ray emission at high luminosities. True Seyfert 2 candidates and double AGN do not show any deviation from the general behaviour. Finally, we show that the MIR--X-ray correlation can be used to verify the AGN nature of uncertain objects. Specifically, we give equations that allow to determine the intrinsic 2-10 keV luminosities and column densities for objects with complex X-ray properties to within 0.34 dex. These techniques are applied to the uncertain objects of the remaining AGN MIR atlas, demonstrating the usefulness of the MIR--X-ray correlation as an empirical tool.Comment: Accepted for publication in MNRAS, 40 pages, 25 figure

Rotação de culturas para o manejo do nematoide reniforme em algodoeiro.

bitstream/item/24264/1/BP201055.pdfDocumento on-line

NGC 1068: No change in the mid-IR torus structure despite X-ray variability

Context. Recent NuSTAR observations revealed a somewhat unexpected increase in the X-ray flux of the nucleus of NGC 1068. We expect the infrared emission of the dusty torus to react on the intrinsic changes of the accretion disk. Aims. We aim to investigate the origin of the X-ray variation by investigating the response of the mid-infrared environment. Methods. We obtained single-aperture and interferometric mid-infrared measurements and directly compared the measurements observed before and immediately after the X-ray variations. The average correlated and single-aperture fluxes as well as the differential phases were directly compared to detect a possible change in the structure of the nuclear emission on scales of $\sim$ 2 pc. Results. The flux densities and differential phases of the observations before and during the X-ray variation show no significant change over a period of ten years. Possible minor variations in the infrared emission are $\lesssim$ 8 %. Conclusions. Our results suggest that the mid-infrared environment of NGC 1068 has remained unchanged for a decade. The recent transient change in the X-rays did not cause a significant variation in the infrared emission. This independent study supports previous conclusions that stated that the X-ray variation detected by NuSTAR observations is due to X-ray emission piercing through a patchy section of the dusty region.Comment: 6 pages, 5 figures, 3 tables. Accepted for publication on A&

A study of the similarities and differences in the reviewing of selected books of 1974 by the New York Times Book Review and the New York Review of Books

This study deals with the quality of book reviewing by the New York Times Book Review and the New York Review of Books. Thirty-three pairs of reviews of books reviewed in 1974 by both reviewing journals comprised the population of the study. Three areas were examined by means of a weighted checklist: author information, content, information and style information. Length of reviews, qualifications of reviewers, focus on issues in reviews and advocacy of position on issues in reviews were also examined

The subarcsecond mid-infrared view of local active galactic nuclei – I. The N- and Q-band imaging atlas

We present the first subarcsecond-resolution mid-infrared (MIR) atlas of local active galactic nuclei (AGN). Our atlas contains 253 AGN with a median redshift of z = 0.016, and includes all publicly available MIR imaging performed to date with ground-based 8 m class telescopes, a total of 895 independent measurements. Of these, more than 60 % are published here for the first time. We detect extended nuclear emission in at least 21 % of the objects, while another 19 % appear clearly point-like, and the remaining objects cannot be constrained. Where present, elongated nuclear emission aligns with the ionization cones in Seyferts. Subarcsecond resolution allows us to isolate the AGN emission on scales of a few tens of parsecs and to obtain nuclear photometry in multiple filters for the objects. Median spectral energy distributions (SEDs) for the different optical AGN types are constructed and individual MIR 12 and 18 µm continuum luminosities are computed. These range over more than six orders of magnitude. In comparison to the arcsecond-scale MIR emission as probed by Spitzer, the continuum emission is much lower on subarcsecond scales in many cases. The silicate feature strength is similar on both scales and generally appears in emission (absorption) in type I (II) AGN. However, the polycyclic aromatic hydrocarbon emission appears weaker or absent on subarcsecond scales. The differences of the MIR SEDs on both scales are particularly large for AGN/starburst composites and close-by (and weak) AGN. The nucleus dominates over the total emission of the galaxy only at luminosities &gt;1044 erg s-1. The AGN MIR atlas is well suited not only for detailed investigation of individual sources but also for statistical studies of AGN unificatio

Spectroscopic and photometric oscillatory envelope variability during the S Doradus outburst of the Luminous Blue Variable R71

To better understand the LBV phenomenon, we analyze multi-epoch and multi-wavelength spectra and photometry of R71. Pre-outburst spectra are analyzed with the radiative transfer code CMFGEN to determine the star's fundamental stellar parameters. During quiescence, R71 has an effective temperature of $T_\mathrm{{eff}} = 15\,500~K$ and a luminosity of log$(L_*/L_{\odot})$ = 5.78 and is thus a classical LBV, but at the lower luminosity end of this group. We determine its mass-loss rate to $4.0 \times 10^{-6}~M_{\odot}~$yr$^{-1}$. We present R71's spectral energy distribution from the near-ultraviolet to the mid-infrared during its present outburst. Mid-infrared observations suggest that we are witnessing dust formation and grain evolution. Semi-regular oscillatory variability in the star's light curve is observed during the current outburst. Absorption lines develop a second blue component on a timescale twice that length. The variability may consist of one (quasi-)periodic component with P ~ 425/850 d with additional variations superimposed. During its current S Doradus outburst, R71 occupies a region in the HR diagram at the high-luminosity extension of the Cepheid instability strip and exhibits similar irregular variations as RV Tau variables. LBVs do not pass the Cepheid instability strip because of core evolution, but they develop comparable cool, low-mass, extended atmospheres in which convective instabilities may occur. As in the case of RV Tau variables, the occurrence of double absorption lines with an apparent regular cycle may be due to shocks within the atmosphere and period doubling may explain the factor of two in the lengths of the photometric and spectroscopic cycles.Comment: 18 pages, 14 figures, submitted to A&