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Astron. Astrophys. 355, 271-290 (2000)

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A model-independent analysis of the variability of GRS 1915+105

T. Belloni 1,2, M. Klein-Wolt 1, M. Méndez 1,3, M. van der Klis 1 and J. van Paradijs 1,4

1 Astronomical Institute "Anton Pannekoek", University of Amsterdam and Center for High-Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
3 Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, 1900 La Plata, Argentina
4 Physics Department, University of Alabama in Huntsville, Huntsville, AL 35899, USA

Received 25 October 1999 / Accepted 5 January 2000


We analyzed 163 observations of the microquasar GRS 1915+105 made with the Rossi X-ray Timing Explorer (RXTE) in the period 1996-1997. For each observation, we produced light curves and color-color diagrams. We classified the observations in 12 separate classes, based on their count rate and color characteristics. From the analysis of these classes, we reduced the variability of the source to transitions between three basic states: a hard state corresponding to the non-observability of the innermost parts of the accretion disk, and two softer states with a fully observable disk. These two soft states represent different temperatures of the accretion disk, related to different local values of the accretion rate. The transitions between these states can be extremely fast. The source moves between these three states following certain patterns and avoiding others, giving rise to a relatively large but limited number of variability classes. These results are the first step towards a linking of the properties of this exceptional source with standard black-hole systems and with accretion disk models.

Key words: black hole physics – stars: binaries: close – stars: individual: GRS 1915+105 – X-rays: stars

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000