Relativistic Magnetic Explosions

Abstract Many explosive astrophysical events, like magnetars’ bursts and flares, are magnetically driven. We consider dynamics of such magnetic explosions—relativistic expansion highly magnetized overpressurized clouds. The corresponding qualitatively different from fluid explosions due to the topological constraint conservation flux. Using analytical, relativistic MHD as well force-free calculations, we find that creation a relativistically expanding, causally disconnected flow obeys threshold condition: it requires sufficiently high initial overpressure quick decrease pressure in external medium (the preexplosion wind). In subcritical case cloud just “puffs up” quietly expands with preflare wind. also compact analytical solution Prendergast’s problem—expansion plasma into vacuum.