Hanna Sai, Xiaofeng Wang, Nancy Elias-Rosa, Yi Yang(杨轶), Jujia Zhang, Weili Lin, Jun Mo, Anthony L Piro, Xiangyun Zeng, Reguitti Andrea, Peter Brown, Christopher R Burns, Yongzhi Cai, Achille Fiore, Eric Y Hsiao, Jordi Isern, K Itagaki, Wenxiong Li, Zhitong Li, Priscila J Pessi, M M Phillips, Stefan Schuldt, Melissa Shahbandeh, Maximilian D Stritzinger, Lina Tomasella, Christian Vogl, Bo Wang, Lingzhi Wang, Chengyuan Wu, Sheng Yang, Jicheng Zhang, Tianmeng Zhang, Xinghan Zhang, National Natural Science Foundation of China, Beijing science and Technology Development, Chinese Academy of Sciences, Agencia Nacional de Promoción Científica y Tecnológica (Argentina), Swedish Research Council, Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), European Commission, and Generalitat de Catalunya
H. Sai et al., 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., Financial support for this work has been provided by the National Science Foundation of China (NSFC grants 12033003 and 11633002), the Scholar Program of Beijing Academy of Science and Technology (DZ:BS202002), and the Tencent XPLORER Prize. This work was partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences. J.Z. is supported by the National Natural Science Foundation of China (NSFC, grants 11773067, 12173082, 11403096), by the Youth Innovation Promotion Association, CAS (grant 2018081), and by the Ten Thousand Talents Program of Yunnan for Top-notch Young Talents. A.R. acknowledges support from ANID BECAS/DOCTORADO NACIONAL 21202412. SY acknowledge support from the G.R.E.A.T research environment, funded by Vetenskapsrådet, the Swedish Research Council, project number 2016-06012. Y.-Z. Cai is funded by China Postdoctoral Science Foundation (grant no. 2021M691821). This work has been supported by MINECO grant ESP2017-82674-R, by EU FEDER funds and by grants 2014SGR1458 and CERCA Programe of the Generalitat de Catalunya (JI). The research of Y.Y. is supported through the Bengier-Winslow-Robertson Fellowship. M. Stritzinger is supported by grants from the Villum Fonden (grant number 28021) and the Independent Research Fund Denmark (IRFD; 8021-00170B). Lingzhi Wang is sponsored (in part) by the Chinese Academy of Sciences (CAS), through a grant to the CAS South America Center for Astronomy (CASSACA) in Santiago, Chile. CYW is supported by the National Natural Science Foundation of China (NSFC grants 12003013). BW is supported by the National Key R&D Program of China (No. 2021YFA1600404), the Western Light Project of CAS (No. XBZG-ZDSYS-202117), the science research grants from the China Manned Space Project (No CMS-CSST-2021-A13).