On the behavior of the black hole candidate 1E 1740.7-2942's corona based on long-term INTEGRAL database

TL;DR

This study analyzes a long-term INTEGRAL dataset to understand the corona behavior in the black hole candidate 1E 1740.7-2942, revealing that thermal comptonization dominates its hard X-ray spectra and producing an extensive light curve in Eddington units.

Contribution

It provides the first homogeneous long-term analysis of 1E 1740.7-2942's X-ray spectra, establishing thermal comptonization as the main emission mechanism and creating the longest X-ray light curve in Eddington units.

Findings

Thermal comptonization explains most of the observed spectra.

Produced the longest hard X-ray light curve in Eddington units.

Long-term homogeneous analysis improves understanding of corona behavior.

Abstract

One of the most straightforward ways to explain the hard X-ray spectra observed in X-ray binaries is to assume that comptonization of soft photons from the accretion disk is occurring. The region where this process takes place, called the corona, is characterized by only two parameters: its thermal energy $kT$ and its optical depth $\tau$. Hard X-ray spectra analysis is, thus, an imperative tool in diagnosing the behavior of these parameters. The lack of consistency in obtaining/analysing long-term databases, however, may have been hindering this kind of characterization from being attained. With the aim of better understanding the corona behavior in the black hole candidate 1E 1740.7-2942, we performed a homogeneous analysis for a large hard X-ray data set from the ISGRI telescope on-board the INTEGRAL satellite. Results from modelling the spectra show that, for most of our sample, unsaturated thermal comptonization is the main mechanism responsible for the hard X-ray spectra observed in 1E 1740.7-2942. Moreover, such extensive database allowed us to produce what is probably the longest hard X-ray light curve of 1E 1740.7-2942 and whose units -- due to recent findings regarding dynamical quantities of the system -- could be expressed in % of Eddington's luminosity.