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Abstract Seeing pristine material from the donor star in a type Ia supernova (SN Ia) explosion can reveal the nature of the binary system. In this paper, we present photometric and spectroscopic observations of SN 2020esm, one of the best-studied SNe of the class of “super-Chandrasekhar” SNe Ia (SC SNe Ia), with data obtained −12 to +360 days relative to peak brightness, obtained from a variety of ground- and space-based telescopes. Initially misclassified as a type II supernova, SN 2020esm peaked at M B = −19.9 mag, declined slowly (Δ m 15 ( B ) = 0.92 mag), and had particularly blue UV and optical colors at early times. Photometrically and spectroscopically, SN 2020esm evolved similarly to other SC SNe Ia, showing the usual low ejecta velocities, weak intermediate-mass elements, and the enhanced fading at late times, but its early spectra are unique. Our first few spectra (corresponding to a phase of ≳10 days before peak) reveal a nearly pure carbon/oxygen atmosphere during the first days after explosion. This composition can only be produced by pristine material, relatively unaffected by nuclear burning. The lack of H and He may further indicate that SN 2020esm is the outcome of the merger of two carbon/oxygen white dwarfs. Modeling its bolometric light curve, we find an 56 Ni mass of 1.23 − 0.14 + 0.14 M ☉ and an ejecta mass of 1.75 − 0.20 + 0.32 M ☉ , in excess of the Chandrasekhar mass. Finally, we discuss possible progenitor systems and explosion mechanisms of SN 2020esm and, in general, the SC SNe Ia class.
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Possible circumstellar interaction origin of the early excess emission in thermonuclear supernovae
ABSTRACT Type Ia supernovae (SNe Ia) arise from the thermonuclear explosion in binary systems involving carbon–oxygen white dwarfs (WDs). The pathway of WDs acquiring mass may produce circumstellar material (CSM). Observing SNe Ia within a few hours to a few days after the explosion can provide insight into the nature of CSM relating to the progenitor systems. In this paper, we propose a CSM model to investigate the effect of ejecta−CSM interaction on the early-time multiband light curves of SNe Ia. By varying the mass-loss history of the progenitor system, we apply the ejecta−CSM interaction model to fit the optical and ultraviolet (UV) photometric data of eight SNe Ia with early excess. The photometric data of SNe Ia in our sample can be well matched by our CSM model except for the UV-band light curve of iPTF14atg, indicating its early excess may not be due to the ejecta−CSM interaction. Meanwhile, the CSM interaction can generate synchrotron radiation from relativistic electrons in the shocked gas, making radio observations a distinctive probe of CSM. The radio luminosity based on our models suggests that positive detection of the radio signal is only possible within a few days after the explosion at higher radio frequencies (e.g. ∼250 GHz); at lower frequencies (e.g. ∼1.5 GHz), the detection is difficult. These models lead us to conclude that a multimessenger approach that involves UV, optical, and radio observations of SNe Ia a few days past explosion is needed to address many of the outstanding questions concerning the progenitor systems of SNe Ia.
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- Award ID(s):
- 1817099
- PAR ID:
- 10471358
- Publisher / Repository:
- Monthly Notices of the Royal Astronomical Society
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 525
- Issue:
- 1
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 246 to 255
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stad2340
