A 90-year-old man has died of injuries sustained in a fire that tore through his South Boston apartment over the weekend, fire officials said Tuesday. Andrew Pano was pronounced dead Monday at Massachusetts General Hospital, where he had been taken following the one-alarm fire on E Street. An unidentified elderly woman who lived on the top floor of the three-decker is in serious condition at Brigham and Women’s Hospital, officials said. The cause of Saturday’s fire was determined to be an electrical short circuit in Pano’s bedroom, Boston Fire Department spokesman Steve MacDonald said.Catalina Gaitan can be reached at firstname.lastname@example.org. Follow her on Twitter at @catalina_gaitan.