Influence of an Internal Magnetar on Supernova Remnant Expansion

Most of the proposed associations between magnetars and supernova remnantsuffer from age problems. Usually, supernova remnants ages are determined froman approximation of the Sedov-Taylor phase relation between radius and age, fora fixed energy of the explosion ~ 10^{51} erg. Those ages do not generallyagree with the characteristic ages of the (proposed) associated magnetars. Weshow quantitatively that, by taking into account the energy injected on thesupernova remnant by magnetar spin-down, a faster expansion results, improvingmatches between characteristic ages and supernova remnants ages. However, themagnetar velocities inferred from observations would inviabilize someassociations. Since characteristic ages may not be good age estimators, theirinfluence on the likelihood of the association may not be as important. In this work we present simple numerical simulations of supernova remnantsexpansion with internal magnetars, and apply it to the observed objects. Ashort initial spin period, thought to be important for the very generation ofthe magnetic field, is also relevant for the modified expansion of the remnant.We next analyze all proposed associations case-by-case, addressing thelikelyhood of each one, according to this perspective. We consider a largerexplosion energy and reasses the characteristic age issue, and conclude thatabout 50% of the associations can be true ones, provided SGRs and AXPs aremagnetars.Comment: 30 pages, AAStex, 5 figures, format fixe