X-ray Spectral Analysis of the Steady States of GRS 1915+105

TL;DR

This study analyzes the X-ray spectral states of GRS 1915+105, revealing distinct soft and hard states with different disk and coronal behaviors, and correlating X-ray and radio emissions to understand accretion processes.

Contribution

It provides a detailed spectral analysis of GRS 1915+105's steady states, identifying correlations between disk, corona, and radio emissions, and linking spectral states to accretion models.

Findings

Steady-soft and steady-hard states are identified with distinct spectral properties.

In steady-hard states, disk truncation varies with accretion rate and correlates with coronal flux.

Radio and X-ray flux correlations follow known tracks, supporting accretion-jet connection models.

Abstract

We report on the X-ray spectral behavior within the steady states of GRS 1915+105. Our work is based on the full data set on the source obtained using the Proportional Counter Array on the Rossi X-ray Timing Explorer and 15 GHz radio data obtained using the Ryle Telescope. The steady observations within the X-ray data set naturally separated into two regions in the color-color diagram and we refer to them as steady-soft and steady-hard. GRS 1915+105 displays significant curvature in the coronal component in both the soft and hard data within the {\it RXTE}/PCA bandpass. A majority of the steady-soft observations displays a roughly constant inner disk radius (R_in), while the steady-hard observations display an evolving disk truncation which is correlated to the mass accretion rate through the disk. The disk flux and coronal flux are strongly correlated in steady-hard observations and very weakly correlated in the steady-soft observations. Within the steady-hard observations we observe two particular circumstances when there are correlations between the coronal X-ray flux and the radio flux with log slopes \eta~0.68 +/- 0.35 and \eta ~ 1.12 +/- 0.13. They are consistent with the upper and lower tracks of Gallo et al. (2012), respectively. A comparison of model parameters to the state definitions show that almost all steady-soft observations match the criteria of either thermal or steep power law state, while a large portion of the steady-hard observations match the hard state criteria when the disk fraction constraint is neglected.