The volumetric rate of calcium-rich transients in the local universe

TL;DR

This paper measures the local universe's calcium-rich transient rate, finding it higher than previous estimates and sufficient to explain observed calcium abundances in galaxy clusters, using data from the Palomar Transient Factory.

Contribution

First measurement of calcium-rich transient rate in the local universe using PTF data, with implications for galaxy cluster chemical enrichment.

Findings

Calcium-rich transient rate is 1.21e-5 events per year per Mpc^3.

Rate accounts for 33-94% of local type Ia supernova rate.

Calcium-rich transients are often offset far from host galaxies.

Abstract

We present a measurement of the volumetric rate of `calcium-rich' optical transients in the local universe, using a sample of three events from the Palomar Transient Factory (PTF). This measurement builds on a detailed study of the PTF transient detection efficiencies, and uses a Monte Carlo simulation of the PTF survey. We measure the volumetric rate of calcium-rich transients to be higher than previous estimates: $1.21^{+1.13}_{-0.39}\times10^{-5}$ events yr$^{-1}$ Mpc$^{-3}$. This is equivalent to 33-94% of the local volumetric type Ia supernova rate. This calcium-rich transient rate is sufficient to reproduce the observed calcium abundances in galaxy clusters, assuming an asymptotic calcium yield per calcium-rich event of ~0.05$\mathrm{M}_{\odot}$. We also study the PTF detection efficiency of these transients as a function of position within their candidate host galaxies. We confirm as a real physical effect previous results that suggest calcium-rich transients prefer large physical offsets from their host galaxies.