A jet model for Galactic black-hole X-ray sources: some constraining correlations

Free access article

Issue		A&A Volume 489, Number 2, October II 2008


Page(s)		481 - 487
Section		Astrophysical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20079159
Published online		23 July 2008

A&A 489, 481-487 (2008)
DOI: 10.1051/0004-6361:20079159

A jet model for Galactic black-hole X-ray sources: some constraining correlations

N. D. Kylafis^{1, 2}, I. E. Papadakis^{1, 2}, P. Reig^{2, 1}, D. Giannios³, and G. G. Pooley⁴

¹ Physics Department, University of Crete, PO Box 2208, 710 03 Heraklion, Crete, Greece
e-mail: kylafis@physics.uoc.gr
² Foundation for Research and Technology-Hellas, PO Box 1527, 711 10 Heraklion, Crete, Greece
³ Max Planck Institute for Astrophysics, Box 1317, 85741 Garching, Germany
⁴ Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, UK

Received 28 November 2007 / Accepted 11 July 2008

Abstract
Context. Some recent observational results impose significant constraints on all the models that have been proposed to explain the Galactic black-hole X-ray sources in the hard state. In particular, it has been found that during the hard state of Cyg X-1 the power-law photon number spectral index, $\Gamma$ , is correlated with the average time lag, $\langle t_{\rm lag}\rangle$ , between hard and soft X-rays. Furthermore, the peak frequencies of the four Lorentzians that fit the observed power spectra are correlated with both $\Gamma$ and $\langle t_{\rm lag}\rangle$ .
Aims. We have investigated whether our jet model can reproduce these correlations.
Methods. We performed Monte Carlo simulations of Compton upscattering of soft, accretion-disk photons in the jet and computed the time lag between hard and soft photons and the power-law index $\Gamma$ of the resulting photon number spectra.
Results. We demonstrate that our jet model naturally explains the above correlations, with no additional requirements and no additional parameters.

Key words: radiation mechanisms: non-thermal -- accretion, accretion disks -- black hole physics -- methods: statistical -- X-rays: binaries

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