The neutron star mass and radius of Aql X‑1 from quiescent X‑ray emissions

We report the quiescent spectra of neutron star (NS) in Aql X‑1 from XMM‑Newton and Chandra. The NS atmosphere model, NSATMOS, is applied to fit the quiescent spectra. The Monte Carlo Markov Chain algorithm is used to constrain the NS mass and radius in Aql X‑1. We find that the absolute flux calibration between XMM‑Newton and Chandra for Aql X‑1 is in good agreement with each other. The NS mass and radius of Aql X‑1 are obtained.