Observations of Supergiant Fast X-ray Transients with LOFT

TL;DR

This paper reviews Supergiant Fast X-ray Transients, highlighting their extreme variability and discussing how the LOFT mission can advance understanding of these enigmatic high mass X-ray binaries.

Contribution

It summarizes current knowledge of SFXTs and explores how LOFT's capabilities will improve their study and understanding.

Findings

LOFT will enhance detection of low luminosity states.

LOFT's sensitivity will improve outburst characterization.

Current knowledge is limited by observational constraints.

Abstract

Supergiant Fast X-ray transients are a subclass of high mass X-ray binaries displaying a peculiar and still poorly understood extreme variability in the X-ray domain. These sources undergo short sporadic outbursts (LX ~ 10^36 - 10^37 erg/s), lasting few ks at the most, and spend a large fraction of their time in an intermediate luminosity state at about LX ~ 10^33 - 10^34 erg/s. The sporadic and hardly predictable outbursts of supergiant fast X-ray transients were so far best discovered by large field of view (FOV) coded-mask instruments; their lower luminosity states require, instead, higher sensitivity focusing instruments to be studied in sufficient details. In this contribution, we provide a summary of the current knowledge on Supergiant Fast X-ray Transients and explore the contribution that the new space mission concept LOFT, the Large Observatory For X-ray Timing, will be able to provide in the field of research of these objects.