On measuring the Hubble constant with X-ray reverberation mapping of active galactic nuclei

We show that X-ray reverberation mapping can be used to measure the distance to type 1 active galactic nuclei (AGNs). This is because X-ray photons originally emitted from the ‘corona’ close to the black hole irradiate the accretion disc and are reemitted with a characteristic ‘reflection’ spectrum that includes a prominent ∼6.4 keV iron emission line. The shape of the reflection spectrum depends ...