High energy characteristics of Neutron star low mass X-ray binaries as seen by INTEGRAL: the 4U 1722-30 case

TL;DR

This study analyzes the long-term energy behavior of the neutron star low mass X-ray binary 4U 1722-30 using INTEGRAL data from 2003 to 2009, revealing persistent emission with multiple outbursts and unique spectral features.

Contribution

It provides a detailed analysis of 4U 1722-30's long-term behavior and proposes a physical explanation for its peculiar 2008 outburst, highlighting its distinct characteristics.

Findings

Persistent emission with multiple bright outbursts

No transition to quiescent state observed

Unique spectral features during the 2008 outburst

Abstract

We report here results on the long time behaviour of the variable source 4U 1722-30, obtained from INTEGRAL non-continuous observations carried out between 2003 and 2009. During this period 4U 1722-30 shows a general persistent emission along with several bright outbursts resembling those of transient X-ray sources/X-ray novae. However the source never switches into a real quiescent state, with very weak or undetectable flux level, as it normally occurs in transient sources. We compare here flux ratios and spectral state variations measured during the different outbursts and highlight the peculiar character of the 2008 outburst, for which we also propose a specific physical explanation.