SUPERNOVA FALLBACK ONTO MAGNETARS AND PROPELLER-POWERED SUPERNOVAE

We explore fallback accretion onto newly born magnetars during the supernova of massive stars. Strong magnetic fields (similar to 10(15) G) and short spin periods (similar to 1-10 ms) have an important influence on how the magnetar interacts with the infalling material. At long spin periods, weak magnetic fields, and high accretion rates, sufficient material is accreted to form a black hole, as is commonly found for massive progenitor stars. When B less than or similar to 5 x 10(14) G, accretion causes the magnetar to spin sufficiently rapidly to deform triaxially and produces gravitational waves, but only for approximate to 50-200 s until it collapses to a black hole. Conversely, at short spin periods, strong magnetic fields, and low accretion rates, the magnetar is in the propeller regime and avoids becoming a black hole by expelling incoming material. This process spins down the magnetar, so that gravitational waves are only expected if the initial protoneutron star is spinning rapidly. Even when the magnetar survives, it accretes at least approximate to 0.3 M-circle dot, so we expect magnetars born within these types of environments to be more massive than the 1.4 M-circle dot typically associated with neutron stars. The propeller mechanism converts the similar to 10(52) erg of spin energy in the magnetar into the kinetic energy of an outflow, which shock heats the outgoing supernova ejecta during the first similar to 10-30 s. For a small similar to 5 M-circle dot hydrogen-poor envelope, this energy creates a brighter, faster evolving supernova with high ejecta velocities similar to(1-3) x 10(4) km s(-1) and may appear as a broad-lined Type Ib/c supernova. For a large greater than or similar to 10 M-circle dot hydrogen-rich envelope, the result is a bright Type IIP supernova with a plateau luminosity of greater than or similar to 10(43) erg s(-1) lasting for a timescale of similar to 60-80 days.