Radiative diffusion in a time-dependent outflow: a model for fast blue optical transients

TL;DR

This paper introduces a radiative diffusion model with a time-dependent outflow to explain Fast Blue Optical Transients, fitting observed light curves and estimating outflow properties, suggesting a massive star collapse origin.

Contribution

It develops a novel radiative diffusion model with a time-dependent outflow to interpret FBOTs, combining analytical and numerical methods for better accuracy.

Findings

Estimated outflow mass of 1-5 solar masses

Ejection duration of a few days

Consistent modeling results for three FBOTs

Abstract

Fast Blue Optical Transients (FBOTs) are luminous transients with fast evolving (typically $t_{\rm rise}<12\ \rm days$) light curve and blue color (usually $\rm {-0.2\ >\ g-r\ >\ -0.3}$) that cannot be explained by a supernova-like explosion. We propose a radiative diffusion in a time-dependent outflow model to interpret such special transients. In this model, we assume a central engine ejects continuous outflow during a few days. We consider the ejection of the outflow to be time-dependent. The outflow is optically thick initially and photons are frozen in it. As the outflow expands over time, photons gradually escape, and our work is to model such an evolution. Numerical and analytical calculations are considered separately, and the results are consistent. We apply the model to three typical FBOTs: PS1-10bjp, ZTF18abukavn, and ATLAS19dqr. The modeling finds the total mass of the outflow ($\sim 1-5 {M_{\odot}}$), and the total time of the ejection ($\sim$ a few days) for them, leading us to speculate that they may be the result of the collapse of massive stars.