possis: predicting spectra, light curves, and polarization for multidimensional models of supernovae and kilonovae

Abstract

We present possis, a time-dependent three-dimensional Monte Carlo code for modelling radiation transport in supernovae and kilonovae. The code incorporates wavelength-and time-dependent opacities and predicts viewing-angle dependent spectra, light curves and polarization for both idealized and hydrodynamical explosion models. We apply the code to a kilonova model with two distinct ejecta components, one including lanthanide elements with relatively high opacities and the other devoid of lanthanides and characterized by lower opacities. We find that a model with total ejecta mass M ej = 0.04 M and half-opening angle of the lanthanide-rich component Φ = 30 • provides a good match to GW 170817/AT 2017gfo for orientations near the polar axis (i.e. for a system viewed close to face-on). We then show how crucial is the use of self-consistent multi-dimensional models in place of combining one-dimensional models to infer important parameters such as the ejecta masses. We finally explore the impact of M ej and Φ on the synthetic observables and highlight how the relatively fast computation times of possis make it well-suited to perform parameter-space studies and extract key properties of supernovae and kilonovae. Spectra calculated with possis in this and future studies will be made publicly available.

Measuring the Hubble constant with a sample of kilonovae

“…The systematics from using a particular kilonova model will remain, but the idea is that a sufficient sample of kilonovae will average out variations in the kilonovae. However, the relative consistency between the results of the two models 24,25 yields some confidence that we are still statistics dominated. We caution that the systematic uncertainty could still be significantly larger than what is assumed here, but the expectation is that the difference between the models should be resolved with future observations.…”

GROWTH on S190814bv: Deep Synoptic Limits on the Optical/Near-infrared Counterpart to a Neutron Star–Black Hole Merger

“…GW170817 faded faster (almost 2 mag in g in 24 hours) and reddened faster (from g − z = −0.3 to +1.3 in 24 hours) than any known or theorized transient (e.g., Cow-perthwaite et al 2017;Kilpatrick et al 2017;Drout et al 2017;Kasliwal et al 2017). Theoretical models (e.g., Tanaka et al 2018;Bulla 2019;Hotokezaka & Nakar 2019) also suggest that kilonovae arising from mergers with at least one NS are rapidly evolving transients. Requiring a photometric evolution faster than 0.1 mag/day to be considered a counterpart candidate is thus conservative, corresponding to evolution more than an order of magnitude slower than GW170817.…”

“…We used the upper limits obtained with DECam and kilonova simulations to constrain the parameter space of the possible EM counterpart to S190814bv. Specifically, we consider the kilonova models developed by Bulla (2019) and Hotokezaka & Nakar (2019).…”

“…We first compare DECam limits to 2D kilonova models computed with the Monte Carlo radiative transfer code possis (Bulla 2019). These models assume a two-component ejecta geometry, with a lanthaniderich component distributed around the equatorial plane and characterized by an half-opening angle φ and a lanthanide-poor component at higher latitudes (see Fig-0 200 400 Figure 7.…”

Extracting high-level information from gamma-ray burst supernova spectra

“…In time domain astrophysics both types of codes have been throughly used to model many different transient sources including: core collapse supernovae (e.g., Hoflich 1991; Baron et al 1995;Fisher 2000;Mazzali et al 2000;Thomas et al 2011;Jerkstrand et al 2012), thermonuclear supernovae (e.g., Kasen et al 2006;Kromer & Sim 2009;Kerzendorf & Sim 2014;Ashall et al 2016;Hoeflich et al 2017;Goldstein & Kasen 2018;Ashall et al 2018), and more recently kilonova (e.g., Tanaka & Hotokezaka 2013;Smartt et al 2017;Bulla 2019). However, previous work has concentrated on the results obtained from these models, and often E-mail:chris.ashall24@gmail.com neglected to explain the exact modeling method, fitting procedure or associated errors.…”