Is Ancestral Katana legal in Standard, Modern, and Commander?

Ancestral Katana is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper.

What type of card is Ancestral Katana?

Ancestral Katana is an Artifact — Equipment. Its oracle text reads: "Whenever a Samurai or Warrior you control attacks alone, you may pay {1}. When you do, attach this Equipment to it. Equipped creature gets +2/+1. Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)"