Radioactive Heating Rate of r-process Elements and Macronova Light Curve

Abstract

We study the heating rate of r-process nuclei and thermalization of decay products in neutron star merger ejecta and macronova (kilonova) light curves. Thermalization of charged decay products, i.e., electrons, α-particles, and fission fragments is calculated according to their injection energy. The γ-ray thermalization processes are also properly calculated by taking the γ-ray spectrum of each decay into account. We show that the β-decay heating rate at later times approaches a powerlaw decline as ∝ t −2.8 , which agrees with the result of Waxman et al. (2019). We present a new analytic model to calculate macronova light curves, in which the density structure of the ejecta is accounted for. We demonstrate that the observed bolometric light curve and temperature evolution of the macronova associated with GW170817 are reproduced well by the β-decay heating rate with the solar r-process abundance pattern. We interpret the break in the observed bolometric light curve around a week as a result of the diffusion wave crossing a significant part of the ejecta rather than a thermalization break. We also show that the time-weighted integral of the bolometric light curve (Katz integral) is useful to provide an estimate of the total r-process mass from the observed data, which is independent of the highly uncertain radiative transfer. For the macronova in GW170817, the ejecta mass is robustly estimated as ≈ 0.05M for A min ≤ 72 and 85 ≤ A min ≤ 130 with the solar r-process abundance pattern. The code for computation of the heating rate and light curve for given initial nuclear abundances is publicly available.

Measuring the Hubble constant with a sample of kilonovae

“…While other models for kilonovae exist at this point, e.g., ref. 32 , they have been shown to give similar light-curve fits to GW170817, and so the expectation is they would give similar results to those here.…”

Implications of the search for optical counterparts during the second part of the Advanced LIGO’s and Advanced Virgo’s third observing run: lessons learned for future follow-up observations

“…To include the uncertainty in distance, we sample from a Gaussian distribution consistent with this uncertainty and add it to the model light curves. In this analysis, we employ three kilonova models based on Kasen et al (2017), Bulla (2019), and Hotokezaka & Nakar (2020), in order to compare any potential systematic effects. These models use similar heating rates (Metzger et al 2010;Korobkin et al 2012), while using different treatments of the radiative transfer.…”

“…Model III (Hotokezaka & Nakar 2020) depends on the ejecta mass M ej , the dividing velocity between the inner and outer component v ej , the lower and upper limit of the velocity distribution v min and v max , and the opacity of the two components, κ low and κ high . We allow the sampling to vary −3 ≤ log 10 (…”

“…4 shows the ejecta mass constraints for S191213g based on the observations from ZTF ( Probability density for the total ejecta mass for the BNS events, S191213g and S200213t, and employed light-curve models. From the left to the right, we show constraints as a function of lanthanide fraction for the Kasen et al (2017) Model, as a function of inclination angle (from a polar orientation, system viewed face-on) for the Bulla (2019) Model, and as a function of the opacity of the two components, κ low and κ high for the Hotokezaka & Nakar (2020) Model. The dashed lines are the upper limits that contain 90 per cent of the probability density.…”

Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey

“…The field of multimessenger astrophysics has experienced dramatic growth in the past few years, thanks to the development and increased sensitivities of instruments like the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO; Aasi et al 2015), the Virgo Interferometer (Acernese et al 2014), IceCube (Achterberg et al 2006), and ANTARES (Ageron et al 2011). Furthermore, real-time alert streams of detections made by instruments such as the Astrophysical Multimessenger Observatory Network (AMON; Smith et al 2013;Keivani et al 2017) and the Gamma-ray Coordination Network (GCN; Barthelmy et al 1998) have made it possible for the astronomical community to target the sources of gravitational waves (Coughlin et al 2019a;Doctor et al 2019;Hosseinzadeh et al 2019;Andreoni et al 2020;Garcia et al 2020, among several others from the previous LIGO/Virgo observing runs) and high-energy neutrinos (Abbasi et al 2012;Aartsen et al 2015;The IceCube Collaboration et al 2018;Kankare et al 2019;Morgan et al 2019;Stein et al 2020, among several others) in search of an electromagnetic signal within hours of the first detection of astrophysical events.…”