An Etymological Dictionary of Astronomy and Astrophysics

A broad → absorption feature observed in → X-ray spectra of → active galactic nuclei (AGN).
It is caused by material associated with the → interstellar medium in our → Galaxy and/or the host galaxy of the AGN or cold material near the AGN.

→ Quasars commonly have their X-ray spectrum absorbed by cold gas between us and the quasar X-ray source (along our → line of sight). This is particularly common in less luminous quasars. See also → warm absorber.

See also: → cold; → absorber.