NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-08-24 T17:46:33 PDT
Help | Comment | NED Home

For refcode 2013A&A...550A..71V:
Retrieve 86 NED objects in this reference.
Please click here for ADS abstract

NED Abstract

Copyright by European Southern Observatory (ESO). Reproduced by permission
2013A&A...550A..71V Variability and the X-ray/UV ratio of active galactic nuclei. II. Analysis of a low-redshift Swift sample Vagnetti, F.; Antonucci, M.; Trevese, D. Abstract. Context. Variability, both in X-ray and optical/UV, affects the well-known anti-correlation between the {alpha}_ox_ spectral index and the UV luminosity of active galactic nuclei, contributing part of the dispersion around the average correlation (intra-source dispersion) in addition to the differences among the time-average {alpha}_ox_ values from source to source (inter-source dispersion). Aims: We aim to evaluate the intrinsic {alpha}_ox_ variations in individual objects and their effect on the dispersion of the {alpha}_ox_ - L_UV_ anti-correlation. Methods: We used simultaneous UV/X-ray data from Swift observations of a low-redshift sample to derive the epoch-dependent {alpha}_ox_(t) indices. We corrected for the host galaxy contribution by a spectral fit of the optical/UV data. We computed ensemble structure functions to analyse the variability of multi-epoch data. Results: We find a strong intrinsic {alpha}_ox_ variability, which significantly contributes (~40% of the total variance) to the dispersion of the {alpha}_ox_ - L_UV_ anti-correlation (intra-source dispersion). The strong X-ray variability and weaker UV variability of this sample are comparable to other samples of low-z active galactic nuclei, and are neither caused by the high fraction of strongly variable narrow line Seyfert 1 galaxies, nor by dilution of the optical variability by the host galaxies. Dilution instead affects the slope of the anti-correlation, which steepens, once corrected, and becomes similar to higher luminosity sources. The structure function of {alpha}_ox_ increases with the time lag up to about one month. This indicates the important contribution of the intermediate-to-long timescale variations, which are possibly generated in the outer parts of the accretion disk. Table 1 is available in electronic form at http://www.aanda.org Key words: surveys, galaxies: active, quasars: general, X-rays: galaxies
Retrieve 86 NED objects in this reference.
Please click here for ADS abstract

Back to NED Home