The INTEGRAL Galactic Plane Scanning

TL;DR

The INTEGRAL Galactic Plane Scanning has provided the most sensitive hard X-ray survey of our Galaxy, discovering numerous transient sources and characterizing their properties, significantly advancing our understanding of the X-ray binary population.

Contribution

This paper presents a comprehensive survey of the Galactic Plane using INTEGRAL, highlighting the detection of transient sources and their variability, which was not previously achieved with such sensitivity.

Findings

Detection of numerous transient sources across various time scales

Most sensitive hard X-ray survey of the Galaxy to date

Characterization of spectral and timing properties of sources

Abstract

After the first nine years of INTEGRAL operational life, the discovery of new sources and source types, a large fraction of which are highly transient or highly absorbed, is certainly one of the most compelling results and legacies of INTEGRAL. Frequent monitoring of the Galactic Plane in AO8 and AO9 campaigns allowed us to detect transient sources, both known and new, confirming that the gamma-ray sky is dominated by the extreme variability of different classes of objects. Regular scans of the Galactic Plane by INTEGRAL provide the most sensitive hard X-ray wide survey to date of our Galaxy, with flux limits of the order of 0.3 mCrab for an exposure time of ~2Ms. Many transient sources have been detected on a wide range of time scales (~hours to months) and identified by triggered followup observations, mainly by Swift/XRT and optical/infrared telescopes. These discoveries are very important to characterize the X-ray binary population in our Galaxy, that is necessary input for evolution studies. The transient source monitoring is crucial to sample a variety of physical conditions corresponding to a large span in luminosity. The long exposure times available allow us to define the spectral and timing properties of the known sources and the global properties of each object class.