Theta class (starship)

The Theta-class raider was a type of starship used by the Miradorn during the 2360s and 70s.

The Theta-class raider was armed with dual forward photon torpedo launchers and dual forward plasma charge emitters and could easily outgun a Starfleet runabout. Its maximum velocity was capable of exceeding warp 5. (DS9: "Vortex")

Background

The runabout's computer identified it as "Miradorn vessel, Theta-class", suggesting this type of vessel is built by this civilization. Of course, it is unlikely that the Miradorn use the Human Greek alphabet, so "theta" may be a Starfleet designation.
Baran's mercenary vessel, later seen in TNG: "Gambit, Part I" and "Gambit, Part II", was not specified as a Theta-class, however, based on its numerous character similarities (maximum warp, similar ship and crew size), same generalized identification (a "mercenary ship"), and unmodified studio model, it may be reasonably assumed that is of the same (or similar) class.
For more information on this studio model, see DS9 studio models.
A model of the Miradorn starship was released by Galoob as part of their Star Trek Micro Machines collection.