High energy spectral study of the black hole Cygnus X-1 with INTEGRAL

TL;DR

This study analyzes extensive INTEGRAL data of Cygnus X-1, classifying spectral states and revealing a persistent high-energy tail in both states, with improved software enabling more accurate flux measurements.

Contribution

The paper introduces a refined method for extracting high-energy spectra and extends the exposure time for the soft state, providing more precise spectral parameters and detection of a hard tail in both states.

Findings

Detection of a high-energy tail in both spectral states.

Extended exposure time for the soft state improves spectral analysis.

Refined software yields lower flux estimates consistent with other instruments.

Abstract

We present the analysis of an extended \textit{INTEGRAL} dataset of the high-mass microquasar Cygnus X-1. We first classify, in a model-independent way, all the \textit{INTEGRAL} individual pointings taken between 2003 and 2016 in three basic spectral states. This, in particular, allows us to triple the exposure time of the soft state in comparison with previous publication. We then study the spectral properties of the 5--400 keV stacked spectra of the soft and hard states and provide the parameters obtained with our modelling. Using a refined alternative method of extracting the Compton double events of the IBIS telescope, we then extract high-energy ($>$400 keV) spectra in the two states. We do detect an hard tail in both states. Our refined analysis allows us to obtain a hard state (count) spectrum at a flux lower than previously published by our team. Although a full estimate of the calibration property of this improved software is still needed, this seems to be more inline with the hard state hard tail seen with other instruments.