Compact remnant mass function: dependence on the explosion mechanism and metallicity Reporter: Chen Wang 06/03/2014 Fryer et al. 2012, ApJ, 749, 91

Outline Introduction Supernova engines Remnant masses from single-star collapse Prescriptions for compact object formation in binaries Conclusions and observational implications

Introduction The mass distribution of neutron stars and stellar-mass black holes provides vital clues into the nature of stellar core collapse and the physical engine responsible for supernova explosions Derive mass distributions of stellar compact remnants with the current understanding of supernova engines.

Introduction —— Accurate measurements NS: from observations of close pulsar binary systems. at least bimodal and likely has a wide spread ranging from low masses up to the maximum BH: from observations of X-ray binaries and modeling of photometric and spectroscopic data extend to high masses (Ozel et al. 2010; Farr et al. 2011) A mass gap between the maximum NS mass and

Introduction Timmes et al. (1996) based their estimates on the iron core masses, predicting a bimodal distribution of remnant masses. (two of the assumptions may lead to erroneous results) Fryer & Kalogera (2001) estimated remnant masses using collapse calculations to guide the relation between initial stellar mass and final remnant mass. NSs: a peak at with a significant tail out to the maximum NS mass. (has been borne out) BHs: an extended, continuous exponential distribution without a mass gap. (the mass gap could be introduced only if a discontinuity exists in the relationship between the supernova explosion energy and progenitor mass. ) mass-loss was neglected !

Introduction —— models Convection-enhanced, neutrino-driven supernova explosion Two post-explosion engines (additional energy is released ) Magnetar Collapsar Fast-convection explosions Delayed-convection explosions This variant will have minimal fallback (rotation)

Supernova engines The remnant formation process : a. stellar collapse and bounce b. convective engine c. post-explosion fallback

a. stellar collapse and bounce Collapse : election capture dissociation of the core elements endothermic Remove the degeneracy pressure Accelerate the compression ! Runaway collapse with velocities comparable to the speed of light

a. stellar collapse and bounce The collapse halts when the core reaches nuclear densities. This abrupt halt causes a bounce shock to move out of the core, starting at The shock moves out until neutrino losses sap its energy reservoir, causing it to stall (at roughly ) M< Energy in neutrinos kinetic energy

b. convective engine M> There is a convective region between the proto-NS where the shock is launched and the position where it stalls. A number of instabilities can develop in the convective region e.g., the Rayleigh-Taylor and the standing accretion shock instability (SASI) Convection-enhanced, neutrino-driven supernova explosion

b. convective engine M>11 Assume that the energy in the supernova explosion is the energy stored in this convective region A supernova explosion occurs if the energy in this region can overcome the ram pressure of the infalling stellar material Time Energy the amount of material accredited onto the proto-NS the amount of fallback

b. convective engine fast–convection explosions (in the first 250ms) delayed-convection explosions (SASI) The total available explosion energy decrease with time A peak near

basic models Rapid model: explosion within the first 250ms an explosion occurs when the accretion rate drops below 3 Delayed model: when the accretion rate drops below 1

Remnant masses from single-star collapse Stars below ~11Msun the fate of collapse is the same for all of explosion models uncertainties: 1. fallback 2. explosion mechanism 3. stellar evolution

Remnant masses from single-star collapse Stars between ~11Msun and ~30Msun determined by the amount of material that falls back onto the proto-NS after the launch of the explosion (energy in the explosion ) Dotted: rapid explosion alone Solid: delayed explosion alone Dot-dashed: rapid explosion with collapsar Dashed: delayed explosion with magnetar

Remnant masses from single-star collapse Stars above ~30Msun depend on the mass loss from stellar wind

Remnant masses from single-star collapse Stars above ~30Msun these mass distributions do not include any additional explosions produced by magnetars or collapsars. magnetar outbursts will prevent fallback, turning some of our BH remnants into NSs. collapsars will limit the amount of BH accretion, turning massive BH systems into low-mass systems

Remnant masses from single-star collapse rapid explosion model

Sources of uncertainty below 11Msun uncertainties in modeling mass loss and convection (the lower limit for NS formation) differences in the results of core-collapse models (the mass of the NSs) Above 11Msun assume that the standard convective engine is the correct engine for most supernova assume the maximum efficiency for ejecting stellar material assume that the proto-NS lacks an energy reservoir All of these effects would drive our final remnant mass lower, so the remnant mass is overestimated

Prescriptions for compact object formation in binaries Binary evolution effectively leads to wider initial progenitor masses for ECS NS formation. Metallicity and wind mass loss may also influence the ECS NS formation range

Observational implications X-ray binary remnant mass distribution Explosion energy distributions of supernovae Gravitational wave signals