CFHT UM2019 - Presentation Details

Abstract Details

Title: AstroSat observation of GX 5-1: Spectral and timing evolution

Presenter: Yashpal Bhulla


We report on the first analysis of AstroSat observation of the Z-source GX 5-1on February 26-27, 2017. The hardness-intensity plot reveals that the source tracedout the horizontal and normal branches. The 0.7-20 keV spectra from simultaneousSXT and LAXPC data at different locations of the hardness-intensity plot can be welldescribed by a disk emission and a thermal Comptonized component. The ratio ofthe disk flux to the total i.e. the disk flux fraction increases monotonically along thehorizontal to the Normal one. Thus, the difference between the Normal and Horizontalbranches is that in the normal branch, the disk dominates the flux while in the horizontal one it is Comptonized component which dominates. The inner disk temperature radii changes dramatically or that the disk is irradiated by the thermal component changing its hardness factor. The power spectra reveal a Quasi periodic Oscillation whose frequency changes from ∼ 30 Hz to 50 Hz. The frequency is found to correlatewell with the disk fraction. In the 3-20 keV LAXPC band the rms of the QPO increaseswith energy as a power-law, while the harder X-ray seems to lag the soft ones with a time-delay of a milliseconds. The results suggest that both the temporal and spectral properties of the source are determined by the geometry of the system which is characterized by the disk flux fraction and that the QPO has its origin in thecorona producing the thermal Comptonized component.