The X-ray spectral properties of X-ray selected AGN : ROSAT spectra of EMSS AGN

Using a sample of 63 AGNs extracted from the $Einstein$ Extended Medium Sensitivity Survey (EMSS), we study the X-ray spectral properties of X-ray selected AGN in the 0.1$-$2.4 keV ROSAT band. These objects are all the EMSS AGN detected with more than 300 net counts in ROSAT PSPC images available from the public archive (as of May 31, 1995). A Maximum-Likelihood analysis is used to find the mean power-law spectral index and the intrinsic dispersion $\sigma_p$. We find =1.42 with $\sigma_p$=0.44. This value is significantly steeper ($\Delta \alpha \sim$0.4) than the mean $Einstein$/IPC spectral index obtained applying the ML analysis on the whole sample of EMSS AGN. This result shows that the soft excess already noted in optically selected AGN is present also in X-ray selected AGN. The relatively high value obtained for the intrinsic dispersion confirms that in the soft band AGN are characterized by a variety of spectral indices and the increase with respect to results obtained from the analysis of Einstein data ($\Delta \sigma_p \sim$0.16) suggests a further broadening of the spectral index distribution as one moves to softer energies. A comparison between the mean spectral index of Radio-quiet and Radio-loud subsamples shows that the mean index of the RL sample is flatter than that of RQ, both in the IPC ($\Delta \alpha \sim$0.3) and in the PSPC ($\Delta \alpha \sim$0.4) data. This suggests that the additional X-ray component in RL AGN dominates the X-ray emission of RL AGN over almost two decades of energy ($\sim$0.1$-$10 keV).Comment: 8 pages LaTex file; mn.sty macro (enclosed), 5 LaTex Tables, 12 Postscript figures; accepted for publication in MNRA

A method for space-variant deblurring with application to adaptive optics imaging in astronomy

Images from adaptive optics systems are generally affected by significant distortions of the point spread function (PSF) across the field of view, depending on the position of natural and artificial guide stars. Image reduction techniques circumventing or mitigating these effects are important tools to take full advantage of the scientific information encoded in AO images. The aim of this paper is to propose a method for the deblurring of the astronomical image, given a set of samples of the space-variant PSF. The method is based on a partitioning of the image domain into regions of isoplanatism and on applying suitable deconvolution methods with boundary effects correction to each region. The effectiveness of the boundary effects correction is proved. Moreover, the criterion for extending the disjoint sections to partially overlapping sections is validated. The method is applied to simulated images of a stellar system characterized by a spatially variable PSF. We obtain good photometric quality, and therefore good science quality, by performing aperture photometry on the deblurred images. The proposed method is implemented in IDL in the Software Package "Patch", which is available on http://www.airyproject.eu.Comment: 11 pages, 9 figures, 7 tables, accepted by A&

End to end numerical simulations of the MAORY multiconjugate adaptive optics system

MAORY is the adaptive optics module of the E-ELT that will feed the MICADO imaging camera through a gravity invariant exit port. MAORY has been foreseen to implement MCAO correction through three high order deformable mirrors driven by the reference signals of six Laser Guide Stars (LGSs) feeding as many Shack-Hartmann Wavefront Sensors. A three Natural Guide Stars (NGSs) system will provide the low order correction. We develop a code for the end-to-end simulation of the MAORY adaptive optics (AO) system in order to obtain high-delity modeling of the system performance. It is based on the IDL language and makes extensively uses of the GPUs. Here we present the architecture of the simulation tool and its achieved and expected performance.Comment: 8 pages, 4 figures, presented at SPIE Astronomical Telescopes + Instrumentation 2014 in Montr\'eal, Quebec, Canada, with number 9148-25

Stellar photometry with Multi Conjugate Adaptive Optics

We overview the current status of photometric analyses of images collected with Multi Conjugate Adaptive Optics (MCAO) at 8-10m class telescopes that operated, or are operating, on sky. Particular attention will be payed to resolved stellar population studies. Stars in crowded stellar systems, such as globular clusters or in nearby galaxies, are ideal test particles to test AO performance. We will focus the discussion on photometric precision and accuracy reached nowadays. We briefly describe our project on stellar photometry and astrometry of Galactic globular clusters using images taken with GeMS at the Gemini South telescope. We also present the photometry performed with DAOPHOT suite of programs into the crowded regions of these globulars reaching very faint limiting magnitudes Ks ~21.5 mag on moderately large fields of view (~1.5 arcmin squared). We highlight the need for new algorithms to improve the modeling of the complex variation of the Point Spread Function across the field of view. Finally, we outline the role that large samples of stellar standards plays in providing a detailed description of the MCAO performance and in precise and accurate colour{magnitude diagrams.Comment: 17 pages, 12 figures, SPIE 201

The VLA-COSMOS Survey: V. 324 MHz continuum observations

We present 90 cm VLA imaging of the COSMOS field, comprising a circular area of 3.14 square degrees at 8.0"x6.0" angular resolution with an average rms of 0.5 mJy/beam. The extracted catalog contains 182 sources (down to 5.5sigma), 30 of which are multi-component sources. Using Monte Carlo artificial source simulations we derive the completeness of the catalog, and we show that our 90 cm source counts agree very well with those from previous studies. Using X-ray, NUV-NIR and radio COSMOS data to investigate the population mix of our 90 cm radio sample, we find that our sample is dominated by active galactic nuclei (AGN). The average 90-20 cm spectral index (S_nu~nu**alpha, where S_nu is the flux density at frequency nu, and alpha the spectral index) of our 90 cm selected sources is -0.70, with an interquartile range of -0.90 to -0.53. Only a few ultra-steep-spectrum sources are present in our sample, consistent with results in the literature for similar fields. Our data do not show clear steepening of the spectral index with redshift. Nevertheless, our sample suggests that sources with spectral indices steeper than -1 all lie at z>1, in agreement with the idea that ultra-steep-spectrum radio sources may trace intermediate-redshift galaxies (z>1).Comment: 10 pages, 12 figures, accepted for publication in MNRA

Exploring MAORY performances through tolerance analysis

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