Hard X-ray emission of the microquasar GRO J1655-40 during the rise of its 2005 outburst

TL;DR

This study analyzes high-energy X-ray data from the 2005 outburst of the microquasar GRO J1655-40, revealing the evolution of a high energy cut-off linked to thermal Comptonization and jet activity.

Contribution

It provides detailed measurements of plasma parameters and the evolution of the high energy cut-off during the outburst rise, integrating INTEGRAL, RXTE, and Swift data.

Findings

High energy cut-off decreased during the outburst rise.

Electron temperature estimated at 30-40 keV.

High energy cut-off disappeared as the jet turned off.

Abstract

We present the analysis of the high energy emission of the Galactic black hole GRO J1655-40 at the beginning of its 2005 outburst. The data from 458 ks of INTEGRAL observations, spread over 4 weeks, are analyzed, along with the existing simultaneous RXTE and Swift data. The high energy data allow us to detect the presence of a high energy cut-off and to study its evolution during the outburst rise. This high energy feature is generally related to thermal mechanisms in the framework of Comptonization models from which we can estimate the plasma parameters. We found an electron temperature of about 30-40 keV and an optical depth around 1.8-2.1. The high energy cut-off decreased along with the radio flux, and disappeared as the jet turned off.