# On the impact of magnetic-field models in galaxy clusters on constraints on axion-like particles from the lack of irregularities in high-energy spectra of astrophysical sources

## TL;DR

This study examines how different magnetic field models in galaxy clusters affect constraints on axion-like particles derived from high-energy spectra, highlighting the importance of magnetic field structure in astrophysical ALP searches.

## Contribution

It introduces the impact of regular magnetic fields on ALP constraints, revising previous limits that assumed purely turbulent fields, and emphasizes the need for detailed magnetic field measurements.

## Key findings

- Regular magnetic fields relax ALP constraints compared to turbulent fields.
- The difference in constraints estimates the theoretical uncertainty in ALP studies.
- Highlights the importance of magnetic field measurements in astrophysical ALP constraints.

## Abstract

Photons may convert to axion-like particles (ALPs) in external magnetic fields. Under certain conditions, this effect should result in irregular features in observed spectra of astrophysical sources. Lack of such irregularities in particular spectra was used to constrain ALP parameters, with two most popular sources being the radio galaxy NGC 1275 and the blazar PKS 2155-304. The effect and, consequently, the constraints, depend on the magnetic fields through which the light from the source is propagated. Here, we revisit ALP constraints from gamma-ray observations of NGC 1275 taking into account the regular magnetic field of the X-ray cavity observed around this radio galaxy. This field was not accounted for in previous studies, which assumed a model of purely turbulent fields with coherence length much smaller than the cavity size. For the purely regular field, ALP constraints are relaxed considerably, compared to the purely turbulent one. While the actual magnetic field around a source is an unknown sum of the turbulent and ordered components, the difference in results gives an estimate of the theoretical uncertainty of the study and calls for detailed measurements of magnetic fields around sources used to constrain ALP properties in this approach.