INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey. Part I: Image Reconstruction

TL;DR

This paper introduces an improved image reconstruction method for the INTEGRAL/IBIS 7-year all-sky hard X-ray survey, significantly reducing systematic noise and enhancing sensitivity, especially near the Galactic Plane and Center.

Contribution

The paper presents novel enhancements to the IBIS/ISGRI image reconstruction technique, including background modeling and wavelet filtering, to improve sensitivity and systematic noise suppression in the survey.

Findings

Systematic noise reduced by ~44% in the Galactic Center region.

Sensitivity improved to 3.7E-12 erg/s/cm2 in the 17-60 keV band.

Survey covers 90% of the sky down to specified flux limits.

Abstract

This paper is the first in a series devoted to the hard X-ray whole sky survey performed by the INTEGRAL observatory over seven years. Here we present an improved method for image reconstruction with the IBIS coded mask telescope. The main improvements are related to the suppression of systematic effects which strongly limit sensitivity in the region of the Galactic Plane (GP), especially in the crowded field of the Galactic Center (GC). We extended the IBIS/ISGRI background model to take into account the Galactic Ridge X-ray Emission (GRXE). To suppress residual systematic artifacts on a reconstructed sky image we applied nonparametric sky image filtering based on wavelet decomposition. The implemented modifications of the sky reconstruction method decrease the systematic noise in the ~20 Ms deep field of GC by ~44%, and practically remove it from the high-latitude sky images. New observational data sets, along with an improved reconstruction algorithm, allow us to conduct the hard X-ray survey with the best currently available minimal sensitivity 3.7E-12 erg/s/cm2 ~0.26 mCrab in the 17-60 keV band at a 5 sigma detection level. The survey covers 90% of the sky down to the flux limit of 6.2E-11 erg/s/cm2 (~4.32 mCrab) and 10% of the sky area down to the flux limit of 8.6E-12 erg/s/cm2 (~0.60 mCrab).