Imaging Analysis of the Hard X-ray Telescope ProtoEXIST2 and New Techniques for High Resolution Coded Aperture Telescopes

TL;DR

This paper presents innovative imaging analysis techniques for high-resolution coded-aperture X-ray telescopes, demonstrated with ProtoEXIST2 balloon data, improving detection sensitivity and background modeling in low photon count scenarios.

Contribution

Introduction of two novel techniques—self-background modeling and Poisson-statistics based significance evaluation—for enhancing high-resolution coded-aperture X-ray imaging.

Findings

Improved detection sensitivity demonstrated with ProtoEXIST2 data.

Effective background modeling using continuous scan or dithering.

Validation of techniques through comparison with simulated backgrounds.

Abstract

Wide-field (> 100 deg$^2$) hard X-ray coded-aperture telescopes with high angular resolution (< 2') will enable a wide range of time domain astrophysics. For instance, transient sources such as gamma-ray bursts can be precisely localized without assistance of secondary focusing X-ray telescopes to enable rapid followup studies. On the other hand, high angular resolution in coded-aperture imaging introduces a new challenge in handling the systematic uncertainty: average photon count per pixel is often too small to establish a proper background pattern or model the systematic uncertainty in a time scale where the model remains invariant. We introduce two new techniques to improve detection sensitivity, which are designed for, but not limited to high resolution coded-aperture system: a self-background modeling scheme which utilizes continuous scan or dithering operations, and a Poisson-statistics based probabilistic approach to evaluate the significance of source detection without subtraction in handling the background. We illustrate these new imaging analysis techniques in high resolution coded-aperture telescope using the data acquired by the wide-field hard X-ray telescope ProtoEXIST2 during the high-altitude balloon flight in Fall, 2012. We review the imaging sensitivity of ProtoEXIST2 during the flight, and demonstrate the performance of the new techniques using our balloon flight data in comparison with simulated ideal Poisson background.