The dynamics of a relativistic blast wave propagating through magnetized
medium is considered taking into account possible inhomogeneities of density
and magnetic field and additional energy supply. Under the simplifying
assumption of a spherically symmetric explosion in a medium with toroidal
magnetic field self-similar solutions for the internal dynamics of the flow are
derived. In the weakly magnetized case, when the bulk of the flow may be
described by the unmagnetized solutions, there is a strongly magnetized sheath
near the contact discontinuity (when it exists). Self-similar solutions inside
the sheath are investigated. In the opposite limit of strongly magnetized
upstream plasma new analytical self-similar solutions are found. Possible
application to the physics of Gamma-Ray Bursts is discussed.Comment: 12 pages, 3 figures, accepted by Physics of Fluid