doi:10.1103/18sn-hxtbengRuz, J.Todarello, E.Vogel, J. K.Rodriguez Candón, F.Giannotti, M.Grefenstette, B.Hudson, H.S.Hannah, I. G.García Irastorza, I.Kim, C. S.Regis, M.Smith, D. M.Taoso, M.Trujillo Bueno, J.NuSTAR as an Axion HelioscopeART-2025-145851We present a novel approach to investigating axions and axionlike particles by studying their potential conversion into x-rays within the Sun’s atmospheric magnetic field. Utilizing high-sensitivity data from the nuclear spectroscopic telescope array (NuSTAR) collected during the 2020 solar minimum, along with advanced solar atmospheric magnetic field models, we establish a new limit on the axion-photon coupling strength ⁢≲7.3×10−12  GeV−1 at 95% CL for axion masses ≲4×10−7  eV. This constraint surpasses current ground-based experimental limits, studying previously unexplored regions of the axion-photon coupling parameter space up to masses of ≲3.4 ×10−4  eV. These findings mark a significant advancement in our ability to probe axion properties and strengthen indirect searches for dark matter candidates.2025http://zaguan.unizar.es/record/16379110.1103/18sn-hxtbhttp://zaguan.unizar.es/record/163791oai:zaguan.unizar.es:163791Physical Review Letters 135, 141001 (2025), 7byhttps://creativecommons.org/licenses/by/4.0/deed.esinfo:eu-repo/semantics/openAccess