Is Crown of Gondor legal in Standard, Modern, and Commander?

Crown of Gondor is legal in: Legacy, Vintage, Commander.

Crown of Gondor

Q: What type of card is Crown of Gondor?

Crown of Gondor is a Legendary Artifact — Equipment. Its oracle text reads: "Equipped creature gets +1/+1 for each creature you control. When a legendary creature you control enters, if there is no monarch, you become the monarch. Equip {4}. This ability costs {3} less to activate if you're the monarch."