2008ApJ...676.1130M -
Astrophys. J., 676, 1130-1150 (2008/April-1)
On the conditions for neutron-rich gamma-ray burst outflows.
METZGER B.D., THOMPSON T.A. and QUATAERT E.
Abstract (from CDS):
We calculate the structure and neutron content of neutrino-heated magnetohydrodynamic winds driven from the surface of newly formed magnetars (``protomagnetars'') and from the midplane of hyperaccreting disks, two of the possible central engines for GRBs and hyperenergetic SNe. Both the surface of protomagnetars and the midplane of neutrino-cooled accretion flows (NDAFs) are electron degenerate and neutron-rich (neutron-to-proton ratio n/p≫1). If this substantial free neutron excess is preserved to large radii in ultrarelativistic outflows, several important observational consequences may result. Weak interaction processes, however, can drive n/p to ∼1 in the nondegenerate regions that obtain just above the surfaces of NDAFs and protomagnetars. Our calculations show that mildly relativistic (Lorentz factor Γ≲10) neutron-rich outflows from NDAFs are possible in the presence of a strong poloidal magnetic field. However, neutron-rich winds possess a minimum mass-loss rate that likely precludes simultaneously neutron-rich and ultrarelativistic (Γ≳100) NDAF winds accompanying a substantial accretion power. In contrast, protomagnetars are capable of producing neutron-rich long-duration GRB outflows ∼10-30 s following core bounce for submillisecond rotation periods; such outflows would, however, accompany only extremely energetic events, in which the GRB+SN energy budget exceeds ∼4x1052 ergs. Neutron-rich highly relativistic outflows may also be produced during some short-duration GRBs by geometrically thick accretion disks formed from compact object mergers. The implications for r-process nucleosynthesis, optical transients due to nonrelativistic neutron-rich winds, and nickel production in protomagnetar and NDAF winds are also briefly discussed.
Abstract Copyright:
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Journal keyword(s):
Accretion, Accretion Disks - Gamma Rays: Bursts - Nuclear Reactions, Nucleosynthesis, Abundances - Stars: Magnetic Fields - Stars: Neutron - Stars: Winds, Outflows - Stars: Supernovae: General
Simbad objects:
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