Cosmological Distance Measurement of 12 Nearby Supernovae IIP with ROTSE-IIIB

TL;DR

This paper introduces a new image differencing technique for ROTSE-IIIb supernova observations, improving detection efficiency and enabling precise distance measurements of nearby Type IIP supernovae to estimate the Hubble constant.

Contribution

The study develops a novel image differencing method for ROTSE data and applies it to measure distances using the Expanding Photosphere Method for Type IIP supernovae.

Findings

20% increase in detection efficiency

Hubble constant measured as 72.9 km/s/Mpc

Method yields competitive distance estimates with limited data

Abstract

We present cosmological analysis of 12 nearby ($z<0.06$) Type IIP supernovae (SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise photometry, we present a new image differencing technique that is implemented for the first time on the ROTSE SN photometry pipeline. With this method, we find up to a 20\% increase in the detection efficiency and significant reduction in residual RMS scatter of the SN lightcurves when compared to the previous pipeline performance. We use the published optical spectra and broadband photometry of well studied SNe IIP to establish temporal models for ejecta velocity and photospheric temperature evolution for our SNe IIP population. This study yields measurements that are competitive to other methods even when the data are limited to a single epoch during the photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and optical spectra, we apply these models to the respective photometric epochs for each SN in the ROTSE IIP sample. This facilitates the use of the Expanding Photosphere Method (EPM) to obtain distance estimates to their respective host galaxies. We then perform cosmological parameter fitting using these EPM distances from which we measure the Hubble constant to be $72.9^{+5.7}_{-4.3}~{\rm kms^{-1}~Mpc^{-1}}$, which is consistent with the standard $\Lambda CDM$ model values derived using other independent techniques.