A Somerset County man accused of sexually assaulting a child in New Jersey was arrested at a Salt Lake City, Utah airport shortly after he landed there, authorities said. The Somerset County Prosecutor’s Office was notified on Oct. 19 by the North Plainfield Police Department that a 9-year-old girl had reported to them that she had been sexually assaulted, according to a joint statement from the agencies. The girl accused Fabian Osuna-Vargas, 39, of North Plainfield, of assaulting her earlier that day in the borough, the statement said. Osuna-Vargas was charged with aggravated sexual assault a…