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Long term variability of Cygnus X-1

By V. Grinberg, N. Hell, K. Pottschmidt, M. Böck, M. A. Nowak, J. Rodriguez, A. Bodaghee, M. Cadolle Bel, G. L. Case, M. Hanke, M. Kühnel, S. B. Markoff, G. G. Pooley, R. E. Rothschild, J. A. Tomsick, C. A. Wilson-Hodge and J. Wilms


International audienceWe present a scheme for determining the spectral state of the canonical black hole Cyg X-1 using data from previous and current X-ray all sky monitors (RXTE-ASM, Swift-BAT, MAXI, and Fermi-GBM). Determinations of the hard/intermediate and soft state agree to better than 10% between different monitors, facilitating the determination of the state and its context for any observation of the source, potentially over the lifetimes of different individual monitors. A separation of the hard and the intermediate states, which strongly differ in their spectral shape and short-term timing behavior, is only possible when data in the soft X-rays (<5 keV) are available. A statistical analysis of the states confirms the different activity patterns of the source (e.g., month- to year-long hard-state periods or phases during which numerous transitions occur). It also shows that the hard and soft states are stable, with the probability of Cyg X-1 remaining in a given state for at least one week to be larger than 85% in the hard state and larger than 75% in the soft state. Intermediate states are short lived, with a 50% probability that the source leaves the intermediate state within three days. Reliable detection of these potentially short-lived events is only possible with monitor data that have a time resolution better than 1 d

Topics: stars: individual: Cygnus X-1, X-rays: binaries, binaries: close, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph]
Publisher: EDP Sciences
Year: 2013
DOI identifier: 10.1051/0004-6361
OAI identifier: oai:HAL:cea-01135394v1
Provided by: Hal-Diderot

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