Following a double shooting at Ruggles station Friday, the alleged gunman and another man with an illegal firearm were arraigned Tuesday, authorities said. Terrell Harris, 19, is accused of shooting two men in the lower busway before fleeing the station, police said. While searching for Harris on an MBTA bus, police allegedly found Kelvin Thames, 18, with a semiautomatic handgun under his seat. Both men were arraigned in Roxbury Municipal Court on charges of unlawful possession of a firearm and related gun charges. Harris faces additional charges of assault and battery with a dangerous weapon, the Suffolk district attorney’s office said. Not-guilty pleas were entered on their behalf.Jennifer Smith can be reached at firstname.lastname@example.org.