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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint 10/03

Long Term Variability of Cyg X-1, II. The rms-Flux Relation

T. Gleissner (1), J. Wilms (1), K. Pottschmidt (2,3), P. Uttley (4), M. A. Nowak (5), R. Staubert (1)

(1) Institut für Astronomie und Astrophysik - Abt. Astronomie, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
(2) Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85748 Garching, Germany
(3) INTEGRAL Science Data Centre, Chemin d'Ecogia 16, 1290 Versoix, Switzerland
(4) School of Physics and Astronomy, University of Southampton, Southampton S017 1BJ, UK
(5) MIT-CXC, NE80-6077, 77 Massachusetts Ave., Cambridge, MA 02139, USA

A&A 414 1091-1104 (2004)

Abstract. We study the long term evolution of the relationship between the root mean square (rms) variability and flux (the "rms-flux relation") for the black hole Cygnus X-1 as monitored from 1996 to 2003 with the Rossi X-ray Timing Explorer (RXTE). We confirm earlier results by Uttley & McHardy (2001) of a linear relationship between rms and flux in the hard state on time scales > 5 s reflecting in its slope the fractional rms variability. We demonstrate the perpetuation of the linear rms-flux relation in the soft and the intermediate state. The existence of a non-zero intercept in the linear rms-flux relation argues for two lightcurve components, for example, one variable and one non-variable component, or a possible constant rms component. The relationship between these two hypothesized components can be described by a fundamental dependence of slope and intercept at time scales ~< 10 ksec with long term averages of the flux.
Key words: black hole physics - stars: individual: Cyg X-1 - X-rays: binaries - X-rays: general

Preprint (764 kb PDF file including figures)
Astrophysics (astro-ph): astro-ph/0311039

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