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Published August 1, 2011 | Published
Journal Article Open

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 (~10^(15) G) and short spin periods (~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 ≾ 5 × 10^(14) G, accretion causes the magnetar to spin sufficiently rapidly to deform triaxially and produces gravitational waves, but only for ≈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 ≈0.3 M_☉, so we expect magnetars born within these types of environments to be more massive than the 1.4 M_☉ typically associated with neutron stars. The propeller mechanism converts the ~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 ~10-30 s. For a small ~5 M_☉ hydrogen-poor envelope, this energy creates a brighter, faster evolving supernova with high ejecta velocities ~(1-3) × 10^4 km s^(–1) and may appear as a broad-lined Type Ib/c supernova. For a large ≳ 10 M_☉ hydrogen-rich envelope, the result is a bright Type IIP supernova with a plateau luminosity of ≳ 10^(43)erg s^(–1) lasting for a timescale of ~60-80 days.

Additional Information

© 2011 The American Astronomical Society. Received 2011 March 31; accepted 2011 May 14; published 2011 July 13. We thank Lars Bildsten, Luc Dessart, Brian Metzger, Robert Quimby, Uli Sperhake, and Todd Thompson for their helpful suggestions. We also thank Evan O'Connor for providing core collapsemodels for initial fallback calculations and estimates of the importance of an accretion disk. This work was supported through NSF grants AST-0855535, PHY-0960291, and OCI-0905046, and by the Sherman Fairchild Foundation. A.L.P. was supported in part by NASA ATP grant NNX07AH06G.

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Published - Piro2011p15614Astrophys_J.pdf


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