Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta

Journal Article · Tue Jul 04 00:00:00 EDT 2017 · Classical and Quantum Gravity

DOI:https://doi.org/10.1088/1361-6382/aa7a77· OSTI ID:1523373

Fernández, Rodrigo ^[1]; Foucart, Francois ^[2]; Kasen, Daniel ^[3]; Lippuner, Jonas ^[4]; Desai, Dhruv ^[5]; Roberts, Luke F. ^[6]

---

1. University of Alberta, Edmonton, AB (Canada); University of California, Berkeley, CA (United States)
2. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Nuclear Science Division
3. University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Nuclear Science Division
4. California Institute of Technology (CalTech), Pasadena, CA (United States)
5. University of California, Berkeley, CA (United States)
6. Michigan State University, East Lansing, MI (United States)

Here we investigate the ejecta from black hole—neutron star mergers by modeling the formation and interaction of mass ejected in a tidal tail and a disk wind. The outflows are neutron-rich, giving rise to optical/infrared emission powered by the radioactive decay of r-process elements (a kilonova). Here we perform an end-to-end study of this phenomenon, where we start from the output of a fully-relativistic merger simulation, calculate the post-merger hydrodynamical evolution of the ejecta and disk winds including neutrino physics, determine the final nucleosynthetic yields using post-processing nuclear reaction network calculations, and compute the kilonova emission with a radiative transfer code. We study the effects of the tail-to-disk mass ratio by scaling the tail density. A larger initial tail mass results in fallback matter becoming mixed into the disk and ejected in the subsequent disk wind. Relative to the case of a disk without dynamical ejecta, the combined outflow has lower mean electron fraction, faster speed, larger total mass, and larger absolute mass free of high-opacity Lanthanides or Actinides. In most cases, the nucleosynthetic yield is dominated by the heavy r-process contribution from the unbound part of the dynamical ejecta. A Solar-like abundance distribution can however be obtained when the total mass of the dynamical ejecta is comparable to the mass of the disk outflows. The kilonova has a characteristic duration of 1 week and a luminosity of ~ 10⁴¹ erg s^-1 , with orientation effects leading to variations of a factor ~2 in brightness. At early times (< 1 d) the emission includes an optical component from the (hot) Lanthanide-rich material, but the spectrum evolves quickly to the infrared thereafter.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF); National Aeronautics and Space Administration (NASA); University of Alberta; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC02-05CH11231; AST-1206097; PF4-150122; NAS8-03060
• OSTI ID: 1523373
• Journal Information: Classical and Quantum Gravity, Vol. 34, Issue 15; ISSN 0264-9381
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
accretion
accretion disks
dense matter
gravitational waves
hydrodynamics
neutrinos
nuclear reactions
nucleosynthesis
abundances.