Sensitivity of the Cherenkov Telescope Array to the Detection of Intergalactic Magnetic Fields

TL;DR

This paper explores how the Cherenkov Telescope Array can detect intergalactic magnetic fields by analyzing the secondary gamma-ray signals from extragalactic sources, using simulations to improve current limits.

Contribution

It introduces a simulation-based method to assess CTA's sensitivity to IGMF, considering source activity and energy, enhancing current detection capabilities.

Findings

Current IGMF limits can be significantly improved.

Sensitivity depends on source activity duration.

Maximum gamma-ray energy influences detection prospects.

Abstract

Very high energy (VHE; energy $E \gtrsim 100\,$GeV) $\gamma$-rays originating from extragalactic sources undergo pair production with low-energy photons of background radiation fields. These pairs can inverse-Compton-scatter background photons, initiating an electromagnetic cascade. The spatial and temporal structure of this secondary $\gamma$-ray signal is altered as the $e^+e^-$ pairs are deflected in an intergalactic magnetic field (IGMF). We investigate how VHE observations with the future Cherenkov Telescope Array with its high angular resolution and broad energy range, can potentially probe the IGMF. We identify promising sources and simulate $\gamma$-ray spectra over a wide range of values of the IGMF strength and coherence length using the publicly available ELMAG Monte Carlo code. Combining simulated observations in a joint likelihood approach, we find that current limits on the IGMF can be significantly improved. The projected sensitivity depends strongly on the time a source has been $\gamma$-ray active and on the emitted maximum $\gamma$-ray energy.