Discovery and progenitor constraints on the Type Ia supernova 2013gy^⋆

¹ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: simonholmbo@phys.au.dk; max@phys.au.dk
² Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
³ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
⁴ Department of Physics, Florida State University, 77 Chieftain Way, Tallahassee, FL 32306, USA
⁵ Carnegie Observatories, Las Campanas Observatory, Casilla 601, La Serena, Chile
⁶ Miller Institute for Basic Research in Science, University of California, Berkeley, CA 94720, USA
⁷ Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA
⁸ Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing, 100084, PR China
⁹ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, PR China
¹⁰ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, PR China
¹¹ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks, Rm 100, Norman, OK 73019-2061, USA
¹² Visiting Astronomer, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹³ Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603 La Serena, Chile
¹⁴ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA
¹⁵ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
¹⁶ INAF, Osservatorio Astronomico di Padova, 35122 Padova, Italy
¹⁷ National Astronomical Observatories of China, Beijing 100012, PR China
¹⁸ School of Science, Tianjin University of Technology, Tianjin 300384, PR China

Received: 5 October 2018
Accepted: 30 January 2019

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 h) 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 ± 0.1). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the Si IIλ6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to R_c ≤ 4 R_⊙. In addition to our early-time constraints, we used a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of < 0.018 M_⊙. Combined, these limits effectively rule out H-rich nondegenerate companions.