Astrophysical limits on very light axion-like particles from Chandra grating spectroscopy of NGC 1275

Understand

Axions/axion-like particles (ALPs) are a well motivated extension of the Standard Model and are generic within String Theory.

• The X-ray transparency of the intracluster medium (ICM) in galaxy clusters is a powerful probe of light ALPs (with mass $<10^{-11}\,{\rm eV}$); as X-ray photons from an embedded or background source propagate through the magnetized ICM, they may undergo energy-dependent quantum mechanical conversion into ALPs (and vice versa), imprinting distortions on the X-ray spectrum.
• We present Chandra data for the active galactic nucleus NGC1275 at the center of the Perseus cluster.
• Employing a 490ks High-Energy Transmission Gratings (HETG) exposure, we obtain a high-quality 1-9keV spectrum free from photon pileup and ICM contamination.