Wind, jet, hybrid corona and hard X-ray flares: multiwavelength evolution of GRO J1655-40 during the 2005 outburst rise

TL;DR

This study analyzes the multiwavelength evolution of GRO J1655-40 during its 2005 outburst, revealing complex interactions between X-ray flares, radio emissions, and winds, modeled with hybrid Comptonization.

Contribution

It demonstrates that a single hybrid Comptonization model with reflection explains the hard X-ray flares without additional components, highlighting the role of non-thermal electrons and winds.

Findings

Hard X-ray flares coincide with radio flares and winds.

A hybrid Comptonization model fits the data during flares.

Winds and radio flares coexist during state transitions.

Abstract

We have investigated the complex multiwavelength evolution of GRO J1655-40 during the rise of its 2005 outburst. We detected two hard X-ray flares, the first one during the transition from the soft state to the ultra-soft state, and the second one in the ultra-soft state. The first X-ray flare coincided with an optically thin radio flare. We also observed a hint of increased radio emission during the second X-ray flare. To explain the hard flares without invoking a secondary emission component, we fit the entire data set with the eqpair model. This single, hybrid Comptonization model sufficiently fits the data even during the hard X-ray flares if we allow reflection fractions greater than unity. In this case, the hard X-ray flares correspond to a Comptonizing corona dominated by non-thermal electrons. The fits also require absorption features in the soft and ultra-soft state which are likely due to a wind. In this work we show that the wind and the optically thin radio flare co-exist. Finally, we have also investigated the radio to optical spectral energy distribution, tracking the radio spectral evolution through the quenching of the compact jet and rise of the optically thin flare, and interpreted all data using state transition models.