Radioactivity and thermalization in the ejecta of compact object mergers and their impact on kilonova light curves

Journal Article · Sat Oct 01 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/829/2/110· OSTI ID:22868640

Barnes, Jennifer; Kasen, Daniel ^[1]; Wu, Meng-Ru; Martínez-Pinedo, Gabriel ^[2]

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1. Departments of Physics and Astronomy, 366 LeConte Hall, University of California, Berkeley, CA 94720 (United States)
2. Institut für Kernphysik (Theoriezentrum), Technische Universität Darmstadt, Schlossgartenstraße 2, D-64289 Darmstadt (Germany)

One promising electromagnetic signature of compact object mergers are kilonovae: approximately isotropic radioactively powered transients that peak days to weeks post-merger. Key uncertainties in kilonova modeling include the emission profiles of the radioactive decay products—non-thermal β-particles, α-particles, fission fragments, and γ-rays—and the efficiency with which their kinetic energy is absorbed by the ejecta. The radioactive energy emitted, along with its thermalization efficiency, sets the luminosity budget and is therefore crucial for predicting kilonova light curves. We outline uncertainties in the radioactivity, describe the processes by which the decay products transfer energy to the ejecta, and calculate time-dependent thermalization efficiencies for each particle type. We determine the net thermalization efficiency and explore its dependence on r-process yields—in particular, the production of α-decaying translead nuclei—and on ejecta mass, velocity, and magnetic fields. We incorporate our results into detailed radiation transport simulations, and calculate updated kilonova light curve predictions. Thermalization effects reduce kilonova luminosities by a factor of roughly 2 at peak, and by an order of magnitude at later times (15 days or more after explosion). We present analytic fits to time-dependent thermalization efficiencies, which can be used to improve light curve models. We revisit the putative kilonova that accompanied gamma-ray burst 130603B, and estimate the mass ejected in that event. We find later time kilonova light curves can be significantly impacted by α-decay from translead isotopes; data at these times may therefore be diagnostic of ejecta abundances.

• OSTI ID: 22868640
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 829; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ALPHA PARTICLES
APPROXIMATIONS
BETA PARTICLES
BLACK HOLES
COMPUTERIZED SIMULATION
COSMIC GAMMA BURSTS
FISSION FRAGMENTS
FORECASTING
LUMINOSITY
MAGNETIC FIELDS
NUCLEAR DECAY
NUCLEOSYNTHESIS
R PROCESS
RADIANT HEAT TRANSFER
RADIATION TRANSPORT
STARS
THERMALIZATION