Speaker
Description
The origin of magnetic fields on cosmological scales remains one of the longstanding problems in cosmology. Magnetic fields observed in galaxies and clusters are typically explained through the amplification of weak seed fields. However, the nature of these weak seed fields remains largely unknown. Two scenarios are usually considered: the cosmological and the astrophysical scenarios.
To distinguish between these formation scenarios, it is crucial to search for signatures of magnetization in cosmic voids, which are regions devoid of large-scale structures. In this context, gamma-ray observations of extragalactic sources offer a powerful tool to measure or constrain the Intergalactic Magnetic Field (IGMF). Very High Energy (VHE) photons (E > 100 GeV) cannot propagate over large distances because they interact with the Extragalactic Background Light (EBL) via γγ pair production. The resulting electron-positron pairs then inverse Compton (IC) scatter photons from the Cosmic Microwave Background (CMB) up to γ-ray energies, initiating an electromagnetic cascade.
If a non-negligible IGMF is present, it deflects the pairs, leading to the so-called pair-echo emission in the case of Gamma-Ray Bursts (GRBs) emitting VHE photons. The characteristics of the pair-echo emission—such as its duration, time extension, and temporal profile—depend on the IGMF, providing a powerful tool to measure or constrain it.
In this contribution, we simulate afterglow emission for GRBs with different physical properties and investigate the possibility of detection of pair-echo emission in the GeV and tens of GeV bands. Specifically, we simulate the pair-echo emission from GRBs located up to redshift 1 for different IGMF configurations. We explore the IGMF strengths for which the pair-echo emission can dominate or compete with the afterglow, as a function of key GRB features such as jet opening angle, distance, and energetics. Our findings provide important predictions for the detection of pair echoes with current and upcoming gamma-ray observatories.
