Timescale Resolved Spectroscopy of Cyg X-1

TL;DR

This paper introduces timescale-resolved spectroscopy (TRS), a new method combining timing and spectral analysis, applied to Cyg X-1, revealing how spectral parameters evolve across different timescales and states.

Contribution

The paper presents TRS as a novel approach that links spectral components to timescales, providing new insights into spectral variability in X-ray binaries.

Findings

TRS produces results consistent with frequency-resolved spectra.

Spectral parameters evolve systematically with timescale.

Different spectral states show distinct timescale-dependent behaviors.

Abstract

We propose the timescale-resolved spectroscopy (TRS) as a new method to combine the timing and spectral study. TRS is based on the time domain power spectrum and reflects the variable amplitudes of spectral components on different timescales. We produce the TRS with the RXTE PCA data for Cyg X-1 and studied the spectral parameters (the power law photon index and the equivalent width of the iron fluorescent line) as a function of timescale. The results of TRS and frequency-resolved spectra (FRS) have been compared, and similarities have been found for the two methods with the identical motivations. We also discover the correspondences between the evolution of photon index with timescale and the evolution of the equivalent width with timescale. The observations can be divided into three types according to the correspondences and different type is connected with different spectral state.