(17) Thomas & Steiman-Cameron, 'V2301 Ophiuchi: An X-ray bright eclipsing AM Herculis
object', ApJ., 515, 404-413 (1999)
Their main contention and they key to their theory is that Nova Cygni 1975 happened in an AM Herculis system, a binary star in which a cool normal star and a highly magnetized white dwarf star are bound together by gravity.
Stockman told SCIENCE NEWS that they can't calculate a value for the field but they estimate it as strong enough to assign the nova to an AM Herculis system.
Spectra indicate the source to be of the AM Herculis
type, in which a white dwarf spins in synchronism with its orbital period around a massive companion.