Improving Sensitivity to Weak Pulsations with Photon Probability Weighting

TL;DR

This paper introduces enhanced statistical tests for gamma-ray pulsar detection that weight photons by their probability of originating from the pulsar, significantly improving sensitivity and background rejection.

Contribution

It develops photon probability weighting methods using instrument response and spectral models, increasing pulsation detection sensitivity by over 50%.

Findings

Sensitivity to pulsars increased by more than 50%.

Null distribution for the H-test extended to complex light curves.

Improved detection may increase the gamma-ray pulsar sample.

Abstract

All gamma-ray telescopes suffer from source confusion due to their inability to focus incident high-energy radiation, and the resulting background contamination can obscure the periodic emission from faint pulsars. In the context of the Fermi Large Area Telescope, we outline enhanced statistical tests for pulsation in which each photon is weighted by its probability to have originated from the candidate pulsar. The probabilities are calculated using the instrument response function and a full spectral model, enabling powerful background rejection. With Monte Carlo methods, we demonstrate that the new tests increase the sensitivity to pulsars by more than 50% under a wide range of conditions. This improvement may appreciably increase the completeness of the sample of radio-loud gamma-ray pulsars. Finally, we derive the asymptotic null distribution for the H-test, expanding its domain of validity to arbitrarily complex light curves.