Very-high-energy quasars hint at ALPs

TL;DR

This paper proposes that photon-axion-like particle (ALP) oscillations within flat spectrum radio quasars can naturally explain the unexpected observation of very-high-energy photons above 30 GeV, challenging existing astrophysical models.

Contribution

It introduces a novel explanation for VHE quasar observations based on photon-ALP oscillations within the source, within the framework of conventional models.

Findings

Photon-ALP oscillations can occur inside FSRQs within allowed parameter ranges.

This mechanism explains the detection of VHE photons above 30 GeV from quasars.

The proposed model aligns with existing astrophysical constraints.

Abstract

One of the mysteries of very-high-energy (VHE) astrophysics is the observation of flat spectrum radio quasars (FSRQs) above about 30 GeV, because at those energies their broad line region should prevent photons produced by the central engine to escape. Although a few astrophysical explanations have been put forward, they are totally ad hoc. We show that a natural explanation emerges within the conventional models of FSRQs provided that photon-ALP oscillations take place inside the source for the model parameters within an allowed range.