分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hanna Sai
Xiaofeng Wang
Nancy Elias-Rosa
Yi Yang
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
摘要： 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.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jing Lu
Eric Y. Hsiao
Mark M. Phillips
Christopher R. Burns
Chris Ashall
Nidia Morrell
Lawrence Ng
Sahana Kumar
Melissa Shahbandeh
Peter Hoeflich
E. Baron
Syed Uddin
Maximilian D. Stritzinger
Nicholas B. Suntzeff
Charles Baltay
Scott Davis
Tiara R. Diamond
Gaston Folatelli
Francisco Förster
Jonathan Gagné
摘要： We present the largest and most homogeneous collection of near-infrared (NIR) spectra of Type Ia Supernovae (SNe Ia): 339 spectra of 98 individual SNe obtained as part of the Carnegie Supernova Project-II. These spectra, obtained with the FIRE spectrograph on the 6.5 m Magellan Baade telescope, have a spectral range of 0.8-2.5 $\mu$m. Using this sample, we explore the NIR spectral diversity of SNe Ia and construct a template of spectral time series as a function of the light-curve-shape parameter, color stretch sBV. Principal Component Analysis is applied to characterize the diversity of the spectral features and reduce data dimensionality to a smaller subspace. Gaussian process regression is then used to model the subspace dependence on phase and light-curve shape and the associated uncertainty. Our template is able to predict spectral variations that are correlated with sBV , such as the hallmark NIR features: Mg II at early times and the H-band break after peak. Using this template reduces the systematic uncertainties in K-corrections by $\sim$90% compared to those from the Hsiao template (Hsiao 2009). These uncertainties are on the level of 4 $\times$ 10$^{-4}$ mag on average. We have also explored a neural network approach using a conditional variational autoencoder that produces promising results for characterizing supernova spectra, though requires a larger data set to assemble comparable quality. This template can serve as the baseline spectral energy distribution for light-curve fitters and can identify peculiar spectral features that might point to compelling physics. The results presented here will substantially improve future SN Ia cosmological experiments, for both nearby and distant samples.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yi Yang
Dietrich Baade
Peter Hoeflich
Lifan Wang
Aleksandar Cikota
Ting-Wan Chen
Jamison Burke
Daichi Hiramatsu
Craig Pellegrino
D. Andrew Howell
Curtis McCully
Stefano Valenti
Steve Schulze
Avishay Gal-Yam
Lingzhi Wang
Alexei V. Filippenko
Keiichi Maeda
Mattia Bulla
Yuhan Yao
Justyn R. Maund
摘要： A rare class of supernovae (SNe) is characterized by strong interaction between the ejecta and several solar masses of circumstellar matter (CSM) as evidenced by strong Balmer-line emission. Within the first few weeks after the explosion, they may display spectral features similar to overluminous Type Ia SNe, while at later phase their observation properties exhibit remarkable similarities with some extreme case of Type IIn SNe that show strong Balmer lines years after the explosion. We present polarimetric observations of SN2018evt obtained by the ESO Very Large Telescope from 172 to 219 days after the estimated time of peak luminosity to study the geometry of the CSM. The nonzero continuum polarization decreases over time, suggesting that the mass loss of the progenitor star is aspherical. The prominent H$\alpha$ emission can be decomposed into a broad, time-evolving component and an intermediate-width, static component. The former shows polarized signals, and it is likely to arise from a cold dense shell (CDS) within the region between the forward and reverse shocks. The latter is significantly unpolarized, and it is likely to arise from shocked, fragmented gas clouds in the H-rich CSM. We infer that SN2018evt exploded inside a massive and aspherical circumstellar cloud. The symmetry axes of the CSM and the SN appear to be similar. SN\,2018evt shows observational properties common to events that display strong interaction between the ejecta and CSM, implying that they share similar circumstellar configurations. Our preliminary estimate also suggests that the circumstellar environment of SN2018evt has been significantly enriched at a rate of $\sim0.1$ M$_\odot$ yr$^{-1}$ over a period of $>100$ yr.
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