We explore fallback accretion onto newly born magnetars during the supernova of massive stars .
Strong magnetic fields ( \sim 10 ^ { 15 } { G } ) and short spin periods ( \sim 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 \lesssim 5 \times 10 ^ { 14 } { G } , accretion causes the magnetar to spin sufficiently rapidly to deform triaxially and produce gravitational waves , but only for \approx 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 \approx 0.3 M _ { \odot } , so we expect magnetars born within these types of environments to be more massive than the 1.4 M _ { \odot } typically associated with neutron stars .
The propeller mechanism converts the \sim 10 ^ { 52 } { ergs } of spin energy in the magnetar into the kinetic energy of an outflow , which shock heats the outgoing supernova ejecta during the first \sim 10 - 30 { s } .
For a small \sim 5 M _ { \odot } hydrogen-poor envelope , this energy creates a brighter , faster evolving supernova with high ejecta velocities \sim ( 1 - 3 ) \times 10 ^ { 4 } { km s ^ { -1 } } and may appear as a broad-lined Type Ib/c supernova .
For a large \gtrsim 10 M _ { \odot } hydrogen-rich envelope , the result is a bright Type IIP supernova with a plateau luminosity of \gtrsim 10 ^ { 43 } { ergs s ^ { -1 } } lasting for a timescale of \sim 60 - 80 { days } .