Standardizing Type Ia supernovae using Near Infrared rebrightening time

TL;DR

This study evaluates the near-infrared rebrightening time (t2) of Type Ia supernovae as a potential standardization parameter, finding it comparable to traditional methods and useful for future cosmological analyses.

Contribution

The paper introduces t2 as an alternative standardization parameter for SNIa brightness, demonstrating its effectiveness compared to stretch and its redundancy when combined with color corrections.

Findings

t2 outperforms stretch in residual scatter without color correction

t2 and stretch provide similar residual scatter when combined with color

t2 could serve as a robustness check in future high-redshift supernova studies

Abstract

Accurate standardisation of Type Ia supernovae (SNIa) is instrumental to the usage of SNIa as distance indicators. We analyse a homogeneous sample of 22 low-z SNIa, observed by the Carnegie Supernova Project (CSP) in the optical and near infra-red (NIR). We study the time of the second peak in the NIR band due to re-brightening, t2, as an alternative standardisation parameter of SNIa peak brightness. We use BAHAMAS, a Bayesian hierarchical model for SNIa cosmology, to determine the residual scatter in the Hubble diagram. We find that in the absence of a colour correction, t2 is a better standardisation parameter compared to stretch: t2 has a 1 sigma posterior interval for the Hubble residual scatter of [0.250, 0.257] , compared to [0.280, 0.287] when stretch (x1) alone is used. We demonstrate that when employed together with a colour correction, t2 and stretch lead to similar residual scatter. Using colour, stretch and t2 jointly as standardisation parameters does not result in any further reduction in scatter, suggesting that t2 carries redundant information with respect to stretch and colour. With a much larger SNIa NIR sample at higher redshift in the future, t2 could be a useful quantity to perform robustness checks of the standardisation procedure.