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Ultraviolet and X-ray variability of active galactic nuclei with Swift
- Publication Year :
- 2016
-
Abstract
- We analyse a sample of 21 active galactic nuclei (AGN) using data from the Swift satellite to study the variability properties of the population in the X-ray, UV and optical band. We find that the variable part of the UV-optical emission has a spectrum consistent with a powerlaw, with an average index of $-2.21\pm0.13$, as would be expected from central illumination of a thin disc (index of -7/3). We also calculate the slope of a powerlaw from UV to X-ray variable emission, $\alpha_{\rm OX,Var}$; the average for this sample is $\alpha_{\rm OX,Var} = -1.06 \pm 0.04$. The anticorrelation of $\alpha_{\rm OX}$ with the UV luminosity, $L_{\rm UV}$, previously found in the average emission is also present in the variable part: $\alpha_{\rm OX,Var} = (-0.177 \pm 0.083) {\rm log} (L_{\rm \nu,Var} (2500\,\AA)) + (3.88 \pm 2.33)$. Correlated variability between the emission in X-rays and UV is detected significantly for 9 of the 21 sources. All these cases are consistent with the UV lagging the X-rays, as would be seen if the correlated UV variations were produced by the reprocessing of X-ray emission. The observed UV lags are tentatively longer than expected for a standard thin disc.<br />ACF, AML and DJKB acknowledge support from the ERC Advanced Grant FEEDBACK 340442. WNA acknowledges support from the European Union Seventh Framework Programme (FP7/2013-2017) under grant agreement n.312789, StrongGravity. DB acknowledges an STFC studentship. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.<br />This is the final version of the article. It first appeared from Oxford University Press via https://doi.org/10.1093/mnras/stw2486
- Subjects :
- Swift
Active galactic nucleus
black hole physics
galaxies: active
FOS: Physical sciences
Astrophysics
01 natural sciences
0103 physical sciences
media_common.cataloged_instance
European union
010303 astronomy & astrophysics
media_common
computer.programming_language
Physics
High Energy Astrophysical Phenomena (astro-ph.HE)
010308 nuclear & particles physics
Astronomy
Astronomy and Astrophysics
Astrophysics - Astrophysics of Galaxies
X-rays: galaxies
13. Climate action
Space and Planetary Science
Astrophysics of Galaxies (astro-ph.GA)
ultraviolet: galaxies
accretion, accretion discs
galaxies: nuclei
Astrophysics - High Energy Astrophysical Phenomena
computer
Subjects
Details
- Language :
- English
- Database :
- OpenAIRE
- Accession number :
- edsair.doi.dedup.....8cd331d66f702e79efd00295c19b3d53