RADIOACTIVITY AND THERMALIZATION IN THE EJECTA OF COMPACT OBJECT MERGERS AND THEIR IMPACT ON KILONOVA LIGHT CURVES

By J. Barnes, D. Kasen, Meng-Ru Wu, G. Mart'inez-Pinedo. 2016

178 citations recorded by the source corpus.

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 -particles, -particles, fission fragments, and -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 -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 -decay from translead isotopes; data at these times may therefore be diagnostic of ejecta abundances.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/f5603d1bc7af8266b30cdd4774f01b8b6217d9f6

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Citations in the corpus

Origin of the heaviest elements: The rapid neutron-capture process (2019, methodology): “the production of actinides with important consequences for late time kilonova light curves (Barnes et al., 2016; Rosswog et al., 2017; Wanajo, 2018; Wu et al., 2019; Zhu et al., 2018; Holmbeck et al., 2019b) and U/Th cosmochronometry (see section VIII.”
Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers (2017, background): “…rates reported here are upper limits to the bolometric luminosities of kilonovae from the disk outflow, since the conversion of energy from radioactive decay products into thermal energy of the ejecta has a limited efficiency (e.g., Metzger et al. 2010; Hotokezaka et al. 2016; Barnes et al. 2016).”
A Magnetar Origin for the Kilonova Ejecta in GW170817 (2018, background): “The thermalization efficiency varies with the density of the mass shell, with a high value at early times ≈0.5–0.7 due to the efficient exchange of beta decay and gamma-ray products (Metzger et al. 2010; Barnes et al. 2016; Hotokezaka et al. 2016; Waxman et al. 2017).”
Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers (2017, methodology): “…with a spherical analytic wind solution, mixed composition opacity, detailed r-process heating from nucleosynthesis network, partitioning of the heating rates between decay products, and individual thermalization of different decay products (following the approach of Barnes et al. 2016).”
Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes (2017, background): “…to generate a relatively rapidly evolving optical/infrared transient—referred to as kilonova or macronova (e.g., Li & Paczyński 1998; Metzger et al. 2010; Roberts et al. 2011; Barnes & Kasen 2013; Tanaka & Hotokezaka 2013; Kasen, Fernández, & Metzger 2015; Metzger et al. 2015; Barnes et al. 2016).”
The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars (2017, methodology): “Coordinate- and time-dependent thermalization of nuclear energy is calculated using empirical fits developed in Barnes et al. (2016) and Rosswog et al. (2017).”
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South (2017, background): “Our highest-quality spectrum is a good match to a fiducial one-component red kilonova model from Kasen et al. (2017), despite many theoretical uncertainties in the atomic data and heating rate (e.g., Barnes et al. 2016; Hotokezaka et al. 2016).”