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

Kavli Affiliate: Eli Rykoff

| First 5 Authors: Govinda Dhungana, Robert Kehoe, Ryan Staten, Jozsef Vinko, J. Craig Wheeler

| Summary:

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.

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