High-Resolution Measurements with the CTAO Southern Array: The Case for Pulsar Wind Nebulae

TL;DR

The paper demonstrates that future high-resolution gamma-ray observations with the CTAO Southern Array can significantly improve understanding of pulsar wind nebulae by constraining magnetic field and electron distributions, especially when combined with X-ray data.

Contribution

It shows that CTAO's improved angular resolution and novel reconstruction algorithms will enhance the study of PWNe, despite limitations in photon statistics.

Findings

Future CTAO observations can constrain magnetic field and electron distributions in PWNe.

High angular resolution improves model differentiation when combined with X-ray data.

Photon statistics remain a limiting factor at multi-TeV energies.

Abstract

The advent of the Cherenkov Telescope Array Observatory (CTAO) and recent advances in reconstruction of gamma-ray photons with Cherenkov telescopes are bound to push the limit of angular resolution to an unprecedented precision of less than one arcminute at tens of TeV. Naturally, such instrumental improvements open up possibilities for new and interesting scientific studies. We aim to show that the study of pulsar wind nebulae (PWNe) in particular is bound to profit from these high-resolution measurements. This is because PWNe are the dominant Galactic source population at TeV energies, exhibit hard spectra up to hundreds of TeV and from X-ray observations are known to possess plentiful structure on arcminute scales. Using HESS J1813-178 and MSH 15-52 as examples, we create simple leptonic models of the TeV morphology of these sources based on X-ray observations and existing gamma-ray measurements. Then, assuming different models for the exposure and point spread function of the observatory, we create mock observations with the future CTAO southern array. We use these to assess the ability of these observations to differentiate between models and study the physics of these sources, in particular to infer the structure of the magnetic field and electron distributions. We find that future observations with the CTAO southern array at multi-TeV energies - in combination with existing X-ray measurements - will likely be able to constrain the distributions of magnetic field and high-energy electrons in these sources. We demonstrate that the sensitivity of these measurements can be significantly enhanced with the improved angular resolution achievable with novel reconstruction algorithms. However, we also show that in the relevant multi-TeV regime, signal-photon statistics remain a limitation and trading event statistics for improved angular resolution is not necessarily advantageous.