Abstract
Axions may be produced in abundance inside stellar cores and then convert into observable x rays in the Galactic magnetic fields. We focus on the Quintuplet and Westerlund 1 super star clusters, which host large numbers of hot, young stars including Wolf-Rayet stars; these stars produce axions efficiently through the axion-photon coupling. We use Galactic magnetic field models to calculate the expected x-ray flux locally from axions emitted from these clusters. We then combine the axion model predictions with archival Nuclear Spectroscopic Telescope Array (NuSTAR) data from 10-80keV to search for evidence of axions. We find no significant evidence for axions and constrain the axion-photon coupling g_{aγγ}≲3.6×10^{-12} GeV^{-1} for masses m_{a}≲5×10^{-11} eV at 95% confidence.
Highlights
Ultralight axionlike particles that couple weakly to ordinary matter are natural extensions to the standard model
Strong constraints on gaγγ for low-mass axions come from the CERN Axion Solar Telescope (CAST) experiment [9], which searches for axions produced in the Solar plasma that free stream to Earth and convert to x rays in the magnetic field of the CAST detector
We produce some of the strongest constraints to date on gaγγ for ma ≲ 10−9 eV through x-ray observations with the Nuclear Spectroscopic Telescope Array (NuSTAR) telescope [11] of super star clusters (SSCs)
Summary
Ultralight axionlike particles that couple weakly to ordinary matter are natural extensions to the standard model. We show that these stars, and as a result the SSCs, are highly efficient at producing axions with energies ∼10–100 keV through the Primakoff process.
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