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|Title:||The evolution of the disc variability along the hard state of the black hole transient GX 339-4||Authors:||De Marco, B.
|Issue Date:||2015||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||454||Issue:||3||First Page:||2360||Abstract:||We report on the analysis of hard-state power spectral density function (PSD) of GX 339-4 down to the soft X-ray band, where the disc significantly contributes to the total emission. At any luminosity probed, the disc in the hard state is intrinsically more variable than in the soft state. However, the fast decrease of disc variability as a function of luminosity, combined with the increase of disc intensity, causes a net drop of fractional variability at high luminosities and low energies, which reminds the well-known behaviour of disc-dominated energy bands in the soft state. The peak frequency of the high-frequency Lorentzian (likely corresponding to the high-frequency break seen in active galactic nuclei, AGN) scales with luminosity, but we do not find evidence for a linear scaling. In addition, we observe that this characteristic frequency is energy dependent. We find that the normalization of the PSD at the peak of the high-frequency Lorentzian decreases with luminosity at all energies, though in the soft band this trend is steeper. Together with the frequency shift, this yields quasi-constant high-frequency (5-20 Hz) fractional rms at high energies, with less than 10 per cent scatter. This reinforces previous claims suggesting that the high-frequency PSD solely scales with black hole mass. On the other hand, this constancy breaks down in the soft band (where the scatter increases to ̃30 per cent). This is a consequence of the additional contribution from the disc component, and resembles the behaviour of optical variability in AGN.||Acknowledgments:||This work is based on observations obtained with XMM – Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. GP acknowledges support via the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408) and the Max Planck Society. This project was funded in part by European Research Council Advanced Grant 267697 4-π-sky: Extreme Astrophysics with Revolutionary Radio Telescopes. TMD acknowledges support by the Spanish Ministerio de Economía y competitividad (MINECO) under grant AYA2013-42627. The authors thank the anonymous referee for helpful comments which significantly improved the paper.||URI:||http://hdl.handle.net/20.500.12386/29368||URL:||https://academic.oup.com/mnras/article/454/3/2360/1192378||ISSN:||0035-8711||DOI:||10.1093/mnras/stv1990||Bibcode ADS:||2015MNRAS.454.2360D||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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