X-ray Searches for Axions from Super Star Clusters

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 - 80 keV to search for evidence of axions. We find no significant evidence for axions and constrain the axion-photon coupling $g_{a\gamma \gamma }\lesssim 3.6\times 10^{-12}$ GeV${}^{-1}$ for masses $m_a\lesssim 5\times 10^{-11}$ eV at 95\% confidence.

Comments: 8+18 pages, 3+21 figures, version published in PRL. Supplementary Data at https://github.com/bsafdi/axionSSC