Short answers, pulled from the story.
Astronomers revealed images of Vanth on the 13th of November 2005 using the Hubble Space Telescope. Michael Brown and Terry-Ann Suer identified this faint dot as a satellite during their survey for objects around large trans-Neptunian bodies.
Fiction writer Sonya Taaffe proposed the name Vanth on the 23rd of March 2009 through a blog post by Michael Brown. The International Astronomical Union approved the name after assessing standard procedures, and the Minor Planet Center published the official citation on the 30th of March 2010.
Orcus and Vanth sit approximately 6,800 kilometers apart from each other's centers while revolving around their shared barycenter every 9.54 days. This configuration places the system's balance point outside the body of Orcus itself with Vanth orbiting at an orbital radius of about 5,870 kilometers.
A single observatory in Hokkaido Japan detected a stellar occultation on the 1st of March 2014 that lasted three seconds but did not provide meaningful constraints on the diameter. Five observatories participated in observing another occultation on the 7th of March 2017 which tightly constrained possible diameters assuming a spherical shape for the object.
Hydrodynamic simulations by Sota Arakawa and colleagues suggest an impactor struck Orcus at an oblique angle greater than 45 degrees about 4 billion years ago shortly after the formation of the Solar System. The collision left a large fragment in orbit that eventually became Vanth while both bodies remained molten for at least 10,000 years allowing tidal interactions to circularize the orbit.