Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Yuan Qi Ni
Dae-Sik Moon
Maria R. Drout
Abigail Polin
David J. Sand
Santiago Gonzalez-Gaitan
Sang Chul Kim
Youngdae Lee
Hong Soo Park
D. Andrew Howell
Peter E. Nugent
Anthony L. Piro
Peter J. Brown
Lluis Galbany
Jamison Burke
Daichi Hiramatsu
Griffin Hosseinzadeh
Stefano Valenti
Niloufar Afsariardchi
Jennifer E. Andrews
Abstract： Type Ia Supernovae are thermonuclear explosions of white dwarf stars. They play a central role in the chemical evolution of the Universe and are an important measure of cosmological distances. However, outstanding questions remain about their origins. Despite extensive efforts to obtain natal information from their earliest signals, observations have thus far failed to identify how the majority of them explode. Here, we present infant-phase detections of SN 2018aoz from a brightness of -10.5 absolute AB magnitudes -- the lowest luminosity early Type Ia signals ever detected -- revealing a hitherto unseen plateau in the $B$-band that results in a rapid redward color evolution between 1.0 and 12.4 hours after the estimated epoch of first light. The missing $B$-band flux is best-explained by line-blanket absorption from Fe-peak elements in the outer 1% of the ejected mass. The observed $B-V$ color evolution of the SN also matches the prediction from an over-density of Fe-peak elements in the same outer 1% of the ejected mass, whereas bluer colors are expected from a purely monotonic distribution of Fe-peak elements. The presence of excess nucleosynthetic material in the extreme outer layers of the ejecta points to enhanced surface nuclear burning or extended sub-sonic mixing processes in some normal Type Ia Supernova explosions.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jeniveve Pearson
Griffin Hosseinzadeh
David J. Sand
Jennifer E. Andrews
Jacob E. Jencson
Yize Dong
K. Azalee Bostroem
Stefano Valenti
Daryl Janzen
Nicolás Meza Retamal
Michael J. Lundquist
Samuel Wyatt
Rachael C. Amaro
Jamison Burke
D. Andrew Howell
Curtis McCully
Daichi Hiramatsu
Saurabh W. Jha
Nathan Smith
Joshua Haislip
Abstract： We present photometric and spectroscopic data of SN 2018lab, a low luminosity type IIP supernova (LLSN) with a V-band peak luminosity of $-15.1\pm0.1$ mag. SN 2018lab was discovered by the Distance Less Than 40 Mpc (DLT40) SNe survey only 0.73 days post-explosion, as determined by observations from the Transiting Exoplanet Survey Satellite (TESS). TESS observations of SN 2018lab yield a densely sampled, fast-rising, early time light curve likely powered by circumstellar medium (CSM) interaction. The blue-shifted, broadened flash feature in the earliest spectra ($<$2 days) of SN 2018lab provide further evidence for ejecta-CSM interaction. The early emission features in the spectra of SN 2018lab are well described by models of a red supergiant progenitor with an extended envelope and close-in CSM. As one of the few LLSNe with observed flash features, SN 2018lab highlights the need for more early spectra to explain the diversity of flash feature morphology in type II SNe.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Yuan Qi Ni
Dae-Sik Moon
Maria R. Drout
Abigail Polin
David J. Sand
Santiago GonzÁlez-GaitÁn
Sang Chul Kim
Youngdae Lee
Hong Soo Park
D. Andrew Howell
Peter E. Nugent
Anthony L. Piro
Peter J. Brown
LluÍs Galbany
Jamison Burke
Daichi Hiramatsu
Griffin Hosseinzadeh
Stefano Valenti
Niloufar Afsariardchi
Jennifer E. Andrews
Abstract： SN~2018aoz is a Type Ia SN with a $B$-band plateau and excess emission in the infant-phase light curves $\lesssim$ 1 day after first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN~2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show the SN is intermediate between two subtypes of normal Type Ia: Core-Normal and Broad-Line. The excess emission could have contributions from the radioactive decay of surface iron-peak elements as well as ejecta interaction with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on H$\alpha$ and He~I favour a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O~I] and He~I disfavours a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN~2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe~II] and [Ni~II]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1-D models are incompatible with the infant-phase excess emission, $B_{\rm max}-V_{\rm max}$ color, and absence of nebular-phase [Ca~II]. Although the explosion processes of SN~2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear normal after $\sim$ 1 day.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Ji-an Jiang
Keiichi Maeda
Miho Kawabata
Mamoru Doi
Toshikazu Shigeyama
Masaomi Tanaka
Nozomu Tominaga
Ken'ichi Nomoto
Yuu Niino
Shigeyuki Sako
Ryou Ohsawa
Malte Schramm
Masayuki Yamanaka
Naoto Kobayashi
Hidenori Takahashi
Tatsuya Nakaoka
Koji S. Kawabata
Keisuke Isogai
Tsutomu Aoki
Sohei Kondo
Abstract： In this Letter we report a discovery of a prominent flash of a peculiar overluminous Type Ia supernova, SN 2020hvf, in about 5 hours of the supernova explosion by the first wide-field mosaic CMOS sensor imager, the Tomo-e Gozen Camera. The fast evolution of the early flash was captured by intensive intranight observations via the Tomo-e Gozen high-cadence survey. Numerical simulations show that such a prominent and fast early emission is most likely generated from an interaction between $0.01~M_{\odot}$ circumstellar material (CSM) extending to a distance of $\sim$$10^{13}~\text{cm}$ and supernova ejecta soon after the explosion, indicating a confined dense CSM formation at the final evolution stage of the progenitor of SN 2020hvf. Based on the CSM-ejecta interaction-induced early flash, the overluminous light curve, and the high ejecta velocity of SN 2020hvf, we suggest that the SN 2020hvf may originate from a thermonuclear explosion of a super-Chandrasekhar-mass white dwarf ("super-$M\rm_{Ch}$ WD"). Systematical investigations on explosion mechanisms and hydrodynamic simulations of the super-$M\rm_{Ch}$ WD explosion are required to further test the suggested scenario and understand the progenitor of this peculiar supernova.
Peer Review Status:Awaiting Review
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