Authorities are investigating the second homicide in Boston this year, an early morning shooting of a man in South Boston on Monday, police said. Police said they responded to to an address on West Second Street at around 2:51 a.m. and found the victim lying on the ground. The man was taken to Tufts Medical Center, where he was pronounced dead, police said. Police did not release the victim’s name or any other details. No arrests have been made.