INTEGRAL observations of Sco X-1: evidence for Comptonization up to 200 keV

TL;DR

This study analyzes extensive INTEGRAL satellite data of Sco X-1, revealing a strong correlation between thermal and nonthermal fluxes, supporting Comptonization as the mechanism for hard X-ray tail production up to 200 keV.

Contribution

It provides the longest IBIS dataset on Sco X-1 and offers evidence that Comptonization explains the hard X-ray tails in this source.

Findings

Strong correlation between thermal and nonthermal fluxes.

Supports Comptonization as the mechanism for hard X-ray tails.

Data covers up to 200 keV, the highest energy range studied.

Abstract

We have analyzed a long-term database for Sco X-1 obtained with the telescope IBIS onboard the INTEGRAL satellite in order to study the hard X-ray behavior of Sco X-1 from 20 up to 200 keV. Besides the data used for producing of the INTEGRAL catalog of sources, this is the longest (412 ks) database of IBIS on Sco X-1 up to date. The production of hard X-ray tails in low-mass X-ray binaries is still a matter of debate. Since most of the fits to the high-energy part of the spectra are done with powerlaw models, the physical mechanism for the hard X-ray tail production is unclear. The purpose of this study is to better constrain those possible mechanisms. Our main result shows a strong correlation between the fluxes in the thermal and nonthermal part of Sco X-1 spectra. We thus suggest that Comptonization of lower energy photons is the mechanism for producing hard X-ray tails in Sco X-1.