The news was reported moments ago by NFL media insider Ian Rapoport, who says the deal is worth one year for three million dollars. Supposedly Johnson turned down twice as much from other teams:
DE Charles Johnson agreed to a 1-year deal with the #Panthers for 3M, source said. He turned down $6M from other teams
— Ian Rapoport (@RapSheet) March 9, 2016
This comes as something of a surprise, of course.
Johnson was in the last year of his contract with Carolina prior to his recent release.