A Dorchester man was arrested early Thursday morning after a search turned up two unsecured loaded guns in his Washington Street apartment, the Suffolk district attorney’s office said. Magnetic Tom, who also goes by Tom Magnetic, 30, pleaded not guilty in Dorchester District Court to two counts each of unlawful possession of a firearm, improper storage of a firearm, and unlawful possession of ammunition, prosecutors said. Tom, who was convicted of drug distribution charges in 2003 and 2005, was arraigned as a Level 2 armed career criminal and was ordered held on $100,000 cash bail.Colin A. Young can be reached firstname.lastname@example.org. Follow him on Twitter@ColinAYoung.