Inflight calibration of SRG/ART-XC point spread function at large off-axis angles

TL;DR

This paper calibrates the off-axis point spread function of the ART-XC telescope using in-flight data, demonstrating its consistency with ground calibration and providing an analytic model for use in all-sky surveys.

Contribution

It presents the first in-flight calibration of the ART-XC PSF at large off-axis angles, including an analytic parametrization as a function of energy.

Findings

The in-flight PSF matches ground calibration results.

The Crab Nebula shows extended structure consistent with Sco X-1.

An analytic model of the PSF as a function of energy is provided.

Abstract

The knowledge of the point spread function (PSF) of the Mikhail Pavlinsky Astronomical Roentgen Telescope - X-ray Concentrator (ART-XC) telescope aboard the Spectrum-Roentgen-Gamma (SRG) observatory plays an especially crucial role in the detection of point X-ray sources in the all-sky survey and the studies of extended X-ray objects with low surface brightness. In this work, we calibrate the far off-axis shape of the ART-XC PSF using in-flight data of Sco X-1 and the Crab Nebula, in all-sky survey or scan mode, respectively. We demonstrate that the so-called "slewing" ART-XC PSF (in contrast to the on-axis PSF), in convolution with the detector pixels, is consistent with ground calibration performed at the Marshall Space Flight Center, and can be used to model the PSF up to large off-axis distances in all-sky survey or scan modes. The radial profile of the Crab Nebula in the 4-12 keV band shows an extended structure out to ~150" and is consistent with Sco X-1 at larger off-axis angles. Finally, we performed an analytic parametrization of the slewing ART-XC PSF as a function of energy.