Relevance of photon-photon dispersion within the jet for blazar axionlike particle searches

TL;DR

This paper investigates how photon-photon dispersion within blazar jets affects ALP-photon mixing, revealing significant impacts at energies above 100 GeV that could influence future gamma-ray observations and ALP searches.

Contribution

It models the jet environment of 3C454.3 to evaluate the impact of various photon fields on ALP-photon mixing, highlighting the importance of including full dispersion effects in such analyses.

Findings

Full dispersion calculations can significantly reduce ALP-photon conversion probability at >100 GeV.

Photon-photon dispersion effects are crucial for accurate ALP searches in gamma-ray astronomy.

Implications for future observations with Cherenkov Telescope Array and similar instruments.

Abstract

Axionlike particles (ALPs) could mix with photons in the presence of astrophysical magnetic fields. Searching for this effect in gamma-ray observations of blazars has provided some of the strongest constraints on ALP parameter space so far. Previously, photon-photon dispersion of gamma-rays off of the CMB has been shown to be important for these calculations, and is universally included in ALP-photon mixing models. Here, we assess the effects of dispersion off of other photon fields within the blazar (produced by the accretion disk, the broad line region, the dust torus, starlight, and the synchrotron field) by modelling the jet and fields of the flat spectrum radio quasar 3C454.3 and propagating ALPs through the model both with and without the full dispersion calculation. We find that the full dispersion calculation can strongly affect the mixing, particularly at energies above 100 GeV -- often reducing the ALP-photon conversion probability. This could have implications for future searches planned with, e.g., the Cherenkov Telescope Array, particularly those looking for a reduced opacity of the universe at the highest energies.