Two Years of INTEGRAL monitoring of GRS 1915+105 Part 2: X-Ray Spectro-Temporal Analysis

TL;DR

This study analyzes two years of INTEGRAL, RXTE, and Ryle Telescope data on GRS 1915+105, revealing correlations between X-ray spectral states, radio flares, and jet ejections, with detailed timing and spectral analysis of cycles and QPOs.

Contribution

It provides new insights into the connection between X-ray spectral/timing features and jet ejections, highlighting the role of the coronal medium as the ejected material.

Findings

Soft X-ray spikes trigger ejections by coinciding with suppression of the coronal hard X-ray component.

The X-ray spectrum during steady state indicates a hard-intermediate state with strong radio emission.

The QPO spectrum differs from the Comptonized component, challenging models of global corona oscillations.

Abstract

(abridged) This is the second paper presenting the results of two years of monitoring of GRS 1915+105 with \integral and \rxte and the Ryle Telescope. We present the X-ray spectral and temporal analysis of four observations which showed strong radio to X-ray correlations. During one observation GRS 1915+105 was in a steady state, while during the three others it showed cycles of X-ray dips and spikes (followed by radio flares). We present the time-resolved spectroscopy of these cyclesand show that in all cases the hard X-ray component (the Comptonized emission from a coronal medium) is suppressed in coincidence with a soft X-ray spike that ends the cycle. We interpret these results as evidence that the soft X-ray spike is the trigger of the ejection, and that the ejected medium is the coronal material. In the steady state observation, the X-ray spectrum is indicative of the hard-intermediate state, with the presence of a relatively strong emission at 15 GHz. The X-ray spectra are the sum of a Comptonized component and an extra power law extending to energies >200 keV without any evidence for a cut-off. We observe a possible correlation of the radio flux with that of the power law component, which may indicate that we see direct emission from the jet at hard X-ray energies. We study the energy dependence of a ~4 Hz QPO during the hard-intermediate state observation. The QPO-``spectrum'' is well modeled by a power law with a cut-off at an energy about 11 keV that clearly differs from the relative contribution of the Comptonized component to the overall flux. This may rule out models of global oscillations of the Compton corona.