Observations of the very young Type Ia Supernova 2019np with early-excess emission
Hanna Sai, Xiaofeng Wang, N. Elias–Rosa, Yi Yang, Jujia Zhang, Weili Lin, Jun Mo, Anthony L. Piro, Xiangyun Zeng, A. Reguitti, P. J. Brown, C. R. Burns, Yongzhi Cai, A. Fiore, E. Y. Hsiao, J. Isern, Kiyoshi Itagaki, Wenxiong Li, Zhitong Li, P. J. Pessi, M. M. Phillips, S. Schuldt, Melissa Shahbandeh, M. Stritzinger, L. Tomasella, C. Vogl, Bo Wang, Lingzhi Wang, Chengyuan Wu, S. Yang, Jicheng Zhang, Tianmeng Zhang, Xinghan Zhang
Abstract
ABSTRACT Early-time radiative signals from Type Ia supernovae (SNe Ia) can provide important constraints on the explosion mechanism and the progenitor system. We present observations and analysis of SN 2019np, a nearby SN Ia discovered within 1–2 days after the explosion. Follow-up observations were conducted in optical, ultraviolet, and near-infrared bands, covering the phases from ∼−16.7 d to ∼+ 367.8 d relative to its B-band peak luminosity. The photometric and spectral evolutions of SN 2019np resemble the average behaviour of normal SNe Ia. The absolute B-band peak magnitude and the post-peak decline rate are Mmax(B) = −19.52 ± 0.47 mag and Δm15(B) = 1.04 ± 0.04 mag, respectively. No Hydrogen line has been detected in the nebular-phase spectra of SN 2019np. Assuming that the 56Ni powering the light curve is centrally located, we find that the bolometric light curve of SN 2019np shows a flux excess up to 5.0 per cent in the early phase compared to the radiative diffusion model. Such an extra radiation perhaps suggests the presence of an additional energy source beyond the radioactive decay of central nickel. Comparing the observed colour evolution with that predicted by different models, such as interactions of SN ejecta with circumstellar matter (CSM)/companion star, a double-detonation explosion from a sub-Chandrasekhar mass white dwarf (WD) and surface 56Ni mixing, we propose that the nickel mixing is more favoured for SN 2019np.