Multiwavelength Observations of GX 339-4 in 1996. II. Rapid X-ray Variability

Abstract

As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present the rapid X-ray variability observed July 26 using the RXTE when the source was in a hard state (= soft X-ray low state). We found that the source was extremely variable, with many bright flares. The flares have relatively symmetric time profiles. There are a few time intervals where the flux rises steadily and then drops suddenly, sometimes to a level lower than the average before the increase. Hardness ratios showed that the source was slightly softer when the flux was brighter. The power density spectra (PDS) were also complicated and we found that broken power laws do not provide adequate fits to any of them. Instead a pair of zero-centered Lorentzians gives a good general description of the shape of the PDS. We found several quasi-periodic oscillations (QPO), including some that are harmonically spaced with the most stable frequency at 0.35 Hz. While the overall rms variability of the source was close to being constant throughout the observation (29% integrating between 0.01 and 50 Hz), there is a small but significant change in the PDS shape with time. More importantly, we show that the soft 2-5 keV band is more variable than the harder 5-10 and 10-40 keV bands, which is unusual for this source and for other black hole candidates. Cross correlation functions (CCF) between these bands show that the light curve for the 10-40 keV band lags that of the 2-5 keV band by 5 msec.

Submitted to Astrophysical Journal. 20 pages. 8 figures

References in corpus (3)

• The EXOSAT data on GX 339-4: further evidence for an ``intermediate'' state
• Multiwavelength Observations of GX 339-4 in 1996. II. Rapid X-ray Variability
• Multiwavelength Observations of GX 339-4 in 1996. III. Keck Spectroscopy

Cited by in corpus (11)

• Radio / X-ray correlation in the low/hard state of GX 339--4
• X-ray and gamma-ray spectra and variability of the black-hole candidate GX 339-4
• Cross-spectral analysis of the X-ray variability of Mrk 421
• Understanding Spectral Variability and Time Lags in Accreting Black Holes
• Impact of reverberation in flared accretion discs on temporal characteristics of X-ray binaries
• The Energy Dependence of the Aperiodic Variability for Cygnus X-1, GX 339-4, GRS 1758-258, & 1E 1740.7-2942
• Simultaneous Observations of GRS 1758-258 in 1997 by VLA, IRAM, SEST, RXTE and OSSE: Spectroscopy and Timing
• A Lack of Radio Emission from Neutron Star Low Mass X-ray Binaries
• Multiwavelength Observations of GX 339-4 in 1996. II. Rapid X-ray Variability
• Multiwavelength Observations of GX 339-4 in 1996. III. Keck Spectroscopy
• Multiwavelength Observations of GX 339-4 in 1996. I. Daily Light Curves and X-ray and Gamma-Ray Spectroscopy