Given the task definition and input, reply with output. From the given sentence, extract the phrase (often noun or verb) that carries the given relationship. The generated phrase should be present in the sentence.

Given Relationship: 'be author of', Sentence: 'In " Guests of the Ayatollah : The First Battle in America 's War With Militant Islam , " Mark Bowden , the celebrated author of " Black Hawk Down , " takes us back to the Iran of 1979 and the America of the Carter White House , painstakingly recounting the 444 days of the Iranian hostage crisis .'
author