NIRCam color–magnitude diagram of the sources in the Westerlund 1 field (gray dots). The red symbols mark the colors and magnitudes of the NIRCam sources with an X-ray counterpart. The dashed lines are PARSEC isochrones with ages of 1 (top), 3, 5, 7, and 9 Myr (bottom), drawn adopting a distance of 4230 pc and A_v=10 mag. The magnitudes corresponding to the masses on the left are taken from the 5 Myr isochrones. The extinction vector is drawn assuming the color excesses provided by the PARSEC website. The crosses on the right show the median error bars in bins of 2 mag in width (e.g., the first, barely visible, point accounts for stars in the 16–18 mag bin).