SRG/ART-XC All-Sky X-ray Survey: Sensitivity Assessment Based on Aperture Photometry

TL;DR

This paper evaluates the sensitivity of the SRG/ART-XC all-sky X-ray survey to point sources using aperture photometry, providing a method to determine flux upper limits across the sky with implications for studying variable and transient sources.

Contribution

It introduces a new sensitivity assessment method based on aperture photometry and statistical approaches, enhancing the analysis of X-ray survey data.

Findings

Consistent upper flux limits obtained via Poisson and Bayesian methods.

The sensitivity assessment aids in identifying variable and transient X-ray sources.

An accessible upper limit service is provided online.

Abstract

The Spectrum-Roentgen-Gamma (SRG) observatory continues to operate successfully in orbit at the Lagrange point L2. The Mikhail Pavlinsky ART-XC telescope has demonstrated high efficiency in conducting X-ray surveys both over large sky regions and the entire celestial sphere. A recently published source catalog, based on data from the first four and partially completed fifth sky scans, contains 1,545 objects detected in the 4-12 keV energy range. In this work, using the same sky survey data, we assess the sensitivity to point source detection across the celestial sphere based on X-ray aperture photometry - that is, we calculate the upper flux limit in the 4-12 keV band at any given significance level. The method is implemented using both Poisson statistics and Bayesian inference, with consistent results between the two approaches. This information is important for studying variable and transient X-ray sources, as well as sources that are not detected with sufficient statistical significance in the ART-XC all-sky survey. The ART-XC upper limit service is available at https://www.srg.cosmos.ru/uplim.