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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint 12/03

Different kinds of long-term variability from Cygnus X-1

S. Benlloch (1), K. Pottschmidt (2,3), J. Wilms (1,4), M.A. Nowak (5), T. Gleissner (1), G.G. Pooley (6)

(1) IAAT - Astronomie, Sand 1, 72076 Tübingen, Germany
(2) MPE, Giessenbachstr. 1, 85748 Garching, Germany
(3) ISDC, Ch. d'Écogia 16, 1290 Versoix, Switzerland
(4) Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
(5) MIT/CSR, Cambridge, MA 02139, USA
(6) Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK

To be published in: Proc. X-Ray Timing 2003: Rossi and Beyond (P. Kaaret, F.K. Lamb, and J.H. Swank eds.), AIP Conf. Proc.

Abstract. We present a study of the long-term variability of Cyg X-1 using data from the RXTE/ASM and the RXTE/PCA during the time between the two soft states of 1996 and 2001/2002. This period has been characterized by many short ASM flaring episodes which we have identified as "failed state transitions". The 150 d period which has been seen before and shortly after the 1996 soft state is not obviously present in the ASM rate during most of this time. Applying selection criteria from our pointed RXTE/PCA observations to exclude the flaring episodes we show that the 150 d period can indeed still be significantly detected in the hard state. Furthermore, while the selected hard state count rate, it is still pronounced in the temporal evolution of the corresponding hardness ratios. The Ryle radio flux is also consistent with the 150 d period being present but distorted during this time.

Preprint (719 kb PDF file including figures)

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