Observations of the very young Type Ia Supernova 2019np with early-excess emission

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 days to ∼+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 Mmax(B) =−19.52 ± 0.47 mag and Δm15(B) =1.04 ± 0.04 mag, respectively. No Hydrogen line has been detected in the near-infrared and 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% 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 56Ni mixing, the latter one is favored.

The Core Normal Type Ia Supernova 2019np: An Overall Spherical Explosion with an Aspherical Surface Layer and an Aspherical 56Ni Core

“…A), where the two uncertainties represent the statistical and the systematic error, respectively. This estimate is consistent with the respective values of 58510.2±0.8 and 58509.64±0.06 reported by Sai et al (2022) and Burke et al (2022). All phases used throughout the present paper are given relative to the 𝐵-band maximum light at MJD 58509.72 (2019-01-26.72).…”

“…All phases used throughout the present paper are given relative to the 𝐵-band maximum light at MJD 58509.72 (2019-01-26.72). A comprehensive study of the SN by Sai et al (2022) concluded that its photometric and spectroscopic properties were similar to those of other normal Type Ia SNe. Sai et al (2022) detected a 5% excess in the early bolometric flux evolution of SN 2019np compared to radiative diffusion models (Arnett 1982;Chatzopoulos et al 2012), hinting at additional energy input compared to the radioactive decay of a Ni core.…”

“…A comprehensive study of the SN by Sai et al (2022) concluded that its photometric and spectroscopic properties were similar to those of other normal Type Ia SNe. Sai et al (2022) detected a 5% excess in the early bolometric flux evolution of SN 2019np compared to radiative diffusion models (Arnett 1982;Chatzopoulos et al 2012), hinting at additional energy input compared to the radioactive decay of a Ni core. They suggested that the blue and relatively fast-rising early light curves of SN 2019np are best fitted with the mixing of 56 Ni from the inner to the outer layers of the SN ejecta (Piro & Morozova 2016).…”

Prospects of Searching for Type Ia Supernovae with 2.5-m Wide Field Survey Telescope

“…The upper panel of Figure 3 displays the distribution of discovered early phase SNe Ia by the hypothesized Deep mode in the space of m dis versus redshift z. Compared with the discovered SNe Ia with early phase observations from ZTF or other studies [18,19,[22][23][24][25][26][27][28]42], the WFST can find much more early phase SNe Ia with higher redshift and fainter brightness. Thus, the Deep observation with the WFST would contribute a substantial sample of SNe Ia with early phase photometric data.…”

“…The early phase observations of SNe 2012cg, 2017cbv, 2018oh, 2019np, 2019yvq, and 2021aefx are also valuable for studying their physical origins [23][24][25][26][27][28].…”