Observations of the Very Young Type Ia Supernova 2019np with Early-excess Emission

• Main Authors: Sai, Hanna, Wang, Xiaofeng, Elias-Rosa, Nancy, Yang, Yi, Zhang, Jujia, Lin, Weili, Mo, Jun, Piro, Anthony L, Zeng, Xiangyun, Andrea, Reguitti, Brown, Peter, Burns, Christopher R, Cai, Yongzhi, Fiore, Achille, Hsiao, Eric Y, Isern, Jordi, Itagaki, K, Li, Wenxiong, Li, Zhitong, Pessi, Priscila J, Phillips, M. M, Schuldt, Stefan, Shahbandeh, Melissa, Stritzinger, Maximilian D, Tomasella, Lina, Vogl, Christian, Wang, Bo, Wang, Lingzhi, Wu, Chengyuan, Yang, Sheng, Zhang, Jicheng, Zhang, Tianmeng, Zhang, Xinghan
• Format: Journal Article
• Language: English
• Published: 01-06-2022
• Subjects: Physics - High Energy Astrophysical Phenomena; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2205.15596

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
$\sim-$16.7 days to $\sim$+367.8 days relative to its $B-$band peak luminosity.
The photometric and spectral evolutions of SN 2019np resembles the average
behavior of normal SNe Ia. The absolute B-band peak magnitude and the post-peak
decline rate are $M_{\rm max}(B)=-19.52 \pm 0.47$mag and $\Delta m_{\rm15}(B)
=1.04 \pm 0.04$mag, respectively. No Hydrogen line has been detected in the
near-infrared and nebular-phase spectra of SN 2019np. Assuming that the
$^{56}$Ni 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% 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 color 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 $^{56}$Ni mixing, the
latter one is favored.