Shu-Ping Yan, a doctoral student whom is advised by Professor Na Wang from Xinjiang Astronomical Observatory, CAS, has analysed the aperiodic X-ray variability and quasi-periodic oscillation (QPO) from the accretion flow in microqusar GRS 1915+105 by using archived data. An convenient and effective technique was developed to analyze the X-ray variability for the first time. The related papers have been published in The Astrophysical Journal (2013, ApJ, 767, 44) and Monthly Notices of the Royal Astronomical Society (2013, MNRAS, 434, 59).

 

Accretion is an important process in the evolutions of celestial bodies. Studying the X-ray variabilities of the accretion flow is one of the most important pathways to understand the flow. GRS 1915+105 produces superluminal radio jets, and shows various X-ray light curves and complex timing phenomena. Even in the χ state, the simplest state of GRS 1915+105, only part of the energy spectra can be explained. According to a comparison between the radio and X-ray emissions, the authors deduced that the jet results in peculiar energy spectra. The analysis on the spectra of the low-frequency QPO amplitude suggested a possible origin of the QPO in the corona. GRS 1915+105 is sometimes in the ρ state during which it oscillates quasi-periodically between two more basic states. The detailed ρ cycle evolution of the low-frequency QPO is also naturally explained by tying the QPO to the corona. The ratio of the power density spectrum (PDS) continuum amplitude spectrum to the QPO amplitude spectrum showed that the accretion disk has high-frequency (> 10 Hz) variations. Due to the dissipation or filter effect of the flow, all of the higher frequency (e.g., > several Hz) variations produced in the disk may be smoothed out, and the observed higher frequency variations might predominantly comes from the corona. The authors thus suggested that the high-frequency disk variations might be contributed to X-ray heating of the disk by the varying corona emission.