Searching for periods in X-ray observations using Kuiper's test. Application to the ROSAT PSPC archive

TL;DR

This paper introduces a Kuiper's test-based method for detecting long-period signals in X-ray data, effectively handling observational discontinuities and contamination, leading to the discovery of 28 new periodic sources in the ROSAT archive.

Contribution

It presents a novel application of Kuiper's test with a semi-analytical trial correction method for long-period detection in X-ray observations.

Findings

Successfully recovered periods in contaminated frequency domains

Identified 28 new periodic-source candidates in ROSAT data

Demonstrated robustness against observational discontinuities

Abstract

We use Kuiper's test to detect periodicities in X-ray and gamma-ray observations. Like Rayleigh's test, it uses the individual photon arrival times, and is therefore well suited to the analysis of faint sources. Our method makes it possible to take into account the discontinuities in the observation, and to completely get rid of the contamination that results from them. This makes it particularly adapted to the search of periods long compared to the total observation duration. We propose a semi-analytical approach to determine the effective number of trial frequencies when searching for unknown periods over a frequency range. This approach can be easily adapted to other tests. We show that, using Kuiper's test, we can recover periods in frequency domains where other tests are completely confused by contamination. We finally search the entire ROSAT Position-Sensitive Proportional Counter (PSPC) archive for long periods, and find 28 new periodic-source candidates.