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Preprint A/02

Coronal-Temporal Correlations in GX339-4: Hysteresis, Possible Reflection Changes, and Implications for ADAFs

Michael A. Nowak (1,2), Joern Wilms (3), James B. Dove (4)

(1) JILA, University of Colorado, Campus Box 440, Boulder, CO 80309-0440, U.S.A.
(2) current address, MIT-CXC, NE80-6077, 77 Massachusetts Ave., Cambridge, MA 02139, U.S.A.
(3) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(4) Dept. of Physics, Metropolitan State College of Denver, C.B. 69, P.O. Box 173362, Denver, CO 80217-3362, U.S.A.

2002, MNRAS 332, 856-878

Abstract. We present spectral fits and timing analysis of Rossi X-ray Timing Explorer observations of GX339-4. These observations were carried out over a span of more than two years and encompassed both the soft/high and hard/low states. Two observations were simultaneous with Advanced Satellite for Cosmology and Astrophysics observations. Hysteresis in the soft state/hard state transition is observed. The hard state exhibits a possible anti-correlation between coronal compactness (i.e., spectral hardness) and the covering fraction of cold, reflecting material. The correlation between 'reflection fraction' and soft X-ray flux, however, appears to be more universal. Furthermore, low flux, hard state observations - taken over a decline into quiescence- show that the Fe line, independent of 'reflection fraction', remains broad and at a roughly constant equivalent width, counter to expectations from ADAF models. All power spectral densities (PSD) of the hard state X-ray lightcurves are describable as the sum of just a few broad, quasi-periodic features with frequencies that roughly scale as coronal compactness, l_c, to the -3/2 power. This is interpretable in a simple, toy model of an efficient spherical corona as variations of l_c ~ R_t, where R_t is the 'transition radius' between the corona and the outer thin disc. Similar to observations of Cyg X-1, time lags between soft and hard variability anti-correlate with coronal compactness. A stronger correlation is seen between the time lags and the 'reflection fraction'. These latter facts might suggest that the time lags are associated with the known, spatially very extended, synchroton emitting outflow.

Key words: -

Paper (753k gzip'ed Postscript including figures), astro-ph/0201383

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