Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe

TL;DR

SN 2009nr, a nearby Type Ia supernova similar to SN 1991T, was observed early thanks to high-cadence all-sky surveys, revealing insights into its luminosity, spectral evolution, and progenitor environment.

Contribution

This study presents early detection and detailed observations of SN 2009nr, highlighting the utility of small telescope surveys for discovering nearby supernovae and challenging assumptions about their progenitor populations.

Findings

SN 2009nr is over-luminous with Mv=-19.6 mag.

Spectral evolution resembles SN 1991T early on, then normal SNe later.

Progenitor likely not associated with young stellar populations.

Abstract

We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the "prompt" component directly correlated with current star formation. The pre-discovery observation of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.