The first 48: Discovery and progenitor constraints on the Type Ia supernova 2013gy

TL;DR

This paper presents early observations and progenitor constraints for SN 2013gy, a normal Type Ia supernova, including its explosion time, companion size limits, and hydrogen mass constraints, enhancing understanding of supernova progenitors.

Contribution

The study provides the earliest detection of SN 2013gy and tight constraints on its progenitor system, including explosion timing and companion star properties, using multi-epoch photometry and nebular spectra.

Findings

Explosion occurred less than 48 hours before discovery.

Companion star radius constrained to ≤ 4 solar radii.

Hydrogen mass stripped from companion limited to < 0.018 solar masses.

Abstract

We present an early-phase $g$-band light curve and visual-wavelength spectra of the normal Type Ia supernova (SN) 2013gy. The light curve is constructed by determining the appropriate S-corrections to transform KAIT natural-system $B$- and $V$-band photometry and Carnegie Supernova Project natural-system $g$-band photometry to the Pan-STARRS1 $g$-band natural photometric system. A Markov Chain Monte Carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of $2.16^{+0.06}_{-0.06}$ and a time of first light of MJD 56629.4$^{+0.1}_{-0.1}$, which is $1.93^{+0.12}_{-0.13}$ days (i.e., $<48$~hr) before the discovery date (2013 December 4.84 UT) and $-19.10^{+0.12}_{-0.13}$ days before the time of $B$-band maximum (MJD 56648.5$\pm0.1$). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the Si II $\lambda$6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to $R_c \leq 4\,R_{\odot}$. In addition to our early-time constraints, we use a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of $< 0.018\,M_{\odot}$. Combined, these limits effectively rule out H-rich nondegenerate companions.