Asteroid 19741, Callahan, was discovered on January 5, 2000 by the Lincoln Laboratory Near-Earth Asteroid Research (LINEAR) Team at Socorro, New Mexico. It has a period of 3 years, 135 days.
It was named for Fairfield, Ohio middle-school teacher Diane Callahan, who mentored a finalist in the 2003 Discovery Channel Youth Science Challenge, a middle school science fair.
Diane Callahan
Possibly the most famous person with the last name Callahan is a fictional character, the iconic San Francisco police detective "Dirty" Harry Callahan, who was known for his tough, expediency-first attitude toward crime and disdain for legal niceties. Another is Father Donald Callahan in Stephen King's novel 'salem's Lot, a Catholic priest who took on a vampire and lost badly due to his wavering faith in his own God.
It is this that seems to inform asteroid Callahan's meaning: tough or jungle-like attitude toward real or perceived anti-social behavior, or its opposite.