How Do Magnetic Field Models Affect Astrophysical Limits on Light Axion-like Particles? An X-Ray Case Study with NGC 1275
Publication Date
2022Journal Title
Astrophysical Journal
ISSN
0004-637X
Publisher
American Astronomical Society
Volume
930
Issue
1
Language
en
Type
Article
This Version
VoR
Metadata
Show full item recordCitation
Matthews, J., Reynolds, C., Marsh, M., Sisk-Reynés, J., & Rodman, P. (2022). How Do Magnetic Field Models Affect Astrophysical Limits on Light Axion-like Particles? An X-Ray Case Study with NGC 1275. Astrophysical Journal, 930 (1) https://doi.org/10.3847/1538-4357/ac5625
Abstract
Axion-like particles (ALPs) are a well-motivated extension to the standard
model of particle physics, and X-ray observations of cluster-hosted AGN
currently place the most stringent constraints on the ALP coupling to
electromagnetism, $g_{a \gamma}$, for very light ALPs ($m_a\lesssim10^{-11}$
eV). We revisit limits obtained by Reynolds et al. (2020) using Chandra X-ray
grating spectroscopy of NGC 1275, the central AGN in the Perseus cluster,
examining the impact of the X-ray spectral model and magnetic field model. We
also present a new publicly available code, ALPro, which we use to solve the
ALP propagation problem. We discuss evidence for turbulent magnetic fields in
Perseus and show that it can be important to resolve the magnetic field
structure on scales below the coherence length. We re-analyse the NGC 1275
X-ray spectra using an improved data reduction and baseline spectral model. We
find the limits are insensitive to whether a partially covering absorber is
used in the fits. At low $m_a$ ($m_a\lesssim10^{-13}$ eV), we find marginally
weaker limits on $g_{a \gamma}$ (by $0.1-0.3$ dex) with different magnetic
field models, compared to Model B from Reynolds et al. (2020). A Gaussian
random field (GRF) model designed to mimic $\sim50$ kpc scale coherent
structures also results in only slightly weaker limits. We conclude that the
existing Model B limits are robust assuming that $\beta_{\rm pl}\approx100$,
and are insensitive to whether cell-based or GRF methods are used. However,
astrophysical uncertainties regarding the strength and structure of cluster
magnetic fields persist, motivating high sensitivity RM observations and
tighter constraints on the radial profile of $\beta_{\rm pl}$.
Keywords
330, High-Energy Phenomena and Fundamental Physics
Sponsorship
Engineering and Physical Sciences Research Council (EP/P020259/1)
Science and Technology Facilities Council (ST/S000623/1)
European Commission Horizon 2020 (H2020) ERC (834203)
STFC (ST/V50659X/1)
Science and Technology Facilities Council (2442592)
Identifiers
apjac5625, ac5625, aas37208
External DOI: https://doi.org/10.3847/1538-4357/ac5625
This record's URL: https://www.repository.cam.ac.uk/handle/1810/336892
Rights
Licence:
http://creativecommons.org/licenses/by/4.0/
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