Ten Microsecond Time Resolution Studies of Cygnus X-1
Abstract
Time variability analyses have be applied to data composed of event times of X-rays emitted from the binary system Cygnus X-1 to search for unique black hole signatures. The X-ray data analyzed was collected at ten microsecond time resolution or better from two instruments, the High Energy Astrophysical Observatory (HEAO) A-1 detector and the Rossi X-ray Timing Explorer (XTE) Proportional Counter Array (PCA). HEAO A-1 and RXTE/PCA collected data from 1979-79 and from 1996 on with energy sensitivity from 1-25 keV and 2-60 keV, respectively. Variability characteristics predicted by various models of an accretion disk around a black hole have be searched for in the data. Drop-offs or quasi-periodic oscillations (QPOs) in the Fourier power spectra are expected from some of these models. A re-examination of an analysis of the Cygnus X-1 data from HEAO A-1 by Meekins, et. al. indicates that the reported excess variability at the ten millisecond time scale can be attributed to instrumental effects. The Fourier spectral technique was applied to the HEAO A-1 and RXTE/PCA data with careful consideration given for correcting the Poisson noise floor for instrumental effects. The resulting noise-subtracted Fourier power spectrum is described by a ~1/f power-law with a break at 3 Hz in the HEAO A-1 data and between 10-20 Hz in the RXTE/PCA data. Evidence for a drop-off may be interpreted from the faster fall off in variability at frequencies greater than the observed breaks. Both breaks occur within the range of Keplerian frequencies associated with the inner edge radii of advection-dominated accretion disks predicted for Cyg X-1. The break between 10-20 Hz is also near the sharp rollover predicted by Nowak and Wagoner's model of accretion disk turbulence. Evidence is seen in the RXTE/PCA data for marginal excess power at frequencies from 100-4000 Hz with 33% of the power spectrum at those frequencies exceeding the 95% confidence level upper limit for detecting a signal in the presence of Poisson noise. No QPOs were observed in the data for quality factors Q > 9 with a 95% confidence level upper limit for the fractional rms amplitude at 1.2% for a 16 Msolar black hole.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1997
- Bibcode:
- 1997PhDT.........6W
- Keywords:
-
- BLACK HOLES;
- Physics: Astronomy and Astrophysics