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 ± 0.1 mag. SN 2018lab was discovered by the ...Distance Less Than 40 Mpc (DLT40) SN 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 ejecta–circumstellar medium (CSM) interaction. The blueshifted, broadened flash feature in the earliest spectra (<2 days) of SN 2018lab provides 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 a 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 the flash feature morphology of Type II SNe.
Abstract
A thermonuclear explosion triggered by a He-shell detonation on a carbon–oxygen white-dwarf core has been predicted to have strong UV line blanketing at early times due to the iron-group ...elements produced during He-shell burning. We present the photometric and spectroscopic observations of SN 2016dsg, a subluminous peculiar Type I supernova consistent with a thermonuclear explosion involving a thick He shell. With a redshift of 0.04, the
i
-band peak absolute magnitude is derived to be around −17.5. The object is located far away from its host, an early-type galaxy, suggesting it originated from an old stellar population. The spectra collected after the peak are unusually red, show strong UV line blanketing and weak O
i
λ
7773 absorption lines, and do not evolve significantly over 30 days. An absorption line around 9700–10500 Å is detected in the near-infrared spectrum and is likely from the unburnt He in the ejecta. The spectroscopic evolution is consistent with the thermonuclear explosion models for a sub-Chandrasekhar-mass white dwarf with a thick He shell, while the photometric evolution is not well described by existing models.
Abstract
We present extensive optical photometric and spectroscopic observations of the high-velocity (HV) Type Ia supernova (SN Ia) 2017fgc, covering the phase from ∼12 days before to ∼389 days ...after maximum brightness. SN 2017fgc is similar to normal SNe Ia, with an absolute peak magnitude of
M
max
B
≈
−19.32 ± 0.13 mag and a post-peak decline of Δ
m
15
(
B
) = 1.05 ± 0.07 mag. Its peak bolometric luminosity is derived as (1.32 ± 0.13) × 10
43
erg s
−1
, corresponding to a
56
Ni mass of 0.51 ± 0.03
M
⊙
. The light curves of SN 2017fgc are found to exhibit excess emission in the
UBV
bands in the early nebular phase and pronounced secondary shoulder/maximum features in the
RrIi
bands. Its spectral evolution is similar to that of HV SNe Ia, with a maximum-light Si
ii
velocity of 15,000 ± 150 km s
−1
and a post-peak velocity gradient of ∼120 ± 10 km s
−1
day
−1
. The Fe
ii
and Mg
ii
lines blended near 4300 Å and the Fe
ii
, Si
ii
, and Fe
iii
lines blended near 4800 Å are obviously stronger than those of normal SNe Ia. Inspecting a large sample reveals that the strength of the two blends in the spectra, and the secondary peak in the
i
/
r
-band light curves, are found to be positively correlated with the maximum-light Si
ii
velocity. Such correlations indicate that HV SNe Ia may experience more complete burning in the ejecta and/or that their progenitors have higher metallicity. Examining the birthplace environment of SN 2017fgc suggests that it likely arose from a stellar environment with young and high-metallicity populations.
Abstract
We present multiband Hubble Space Telescope imaging of the calcium-rich supernova (SN) SN 2019ehk at 276-389 days after explosion. These observations represent the latest
B
-band to near-IR ...photometric measurements of a calcium-rich transient to date and allow for the first opportunity to analyze the late-time bolometric evolution of an object in this observational SN class. We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of
56
Co for which we derive a mass of
M
(
56
Co) = (2.8 ± 0.1) × 10
−2
M
⊙
. Furthermore, the rate of decline in bolometric luminosity requires the leakage of
γ
-rays on timescale
t
γ
= 53.9 ± 1.30 days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta. While our observations cannot constrain the exact masses of other radioactive isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of
M
(
57
Co)/M(
56
Co) ≤ 0.030. This limit is consistent with the explosive nucleosynthesis produced in the merger of low-mass white dwarfs, which is one of the favored progenitor scenarios in early-time studies of SN 2019ehk.
Abstract
We present JWST near-infrared (NIR) and mid-infrared (MIR) spectroscopic observations of the nearby normal Type Ia supernova (SN) SN 2021aefx in the nebular phase at +255 days past maximum ...light. Our Near Infrared Spectrograph (NIRSpec) and Mid Infrared Instrument observations, combined with ground-based optical data from the South African Large Telescope, constitute the first complete optical+NIR+MIR nebular SN Ia spectrum covering 0.3–14
μ
m. This spectrum unveils the previously unobserved 2.5−5
μ
m region, revealing strong nebular iron and stable nickel emission, indicative of high-density burning that can constrain the progenitor mass. The data show a significant improvement in sensitivity and resolution compared to previous Spitzer MIR data. We identify numerous NIR and MIR nebular emission lines from iron-group elements as well as lines from the intermediate-mass element argon. The argon lines extend to higher velocities than the iron-group elements, suggesting stratified ejecta that are a hallmark of delayed-detonation or double-detonation SN Ia models. We present fits to simple geometric line profiles to features beyond 1.2
μ
m and find that most lines are consistent with Gaussian or spherical emission distributions, while the Ar
iii
8.99
μ
m line has a distinctively flat-topped profile indicating a thick spherical shell of emission. Using our line profile fits, we investigate the emissivity structure of SN 2021aefx and measure kinematic properties. Continued observations of SN 2021aefx and other SNe Ia with JWST will be transformative to the study of SN Ia composition, ionization structure, density, and temperature, and will provide important constraints on SN Ia progenitor and explosion models.
Abstract
We present space-based ultraviolet/optical photometry and spectroscopy with the
Swift
Ultra-Violet/Optical Telescope and
Hubble Space Telescope
(
HST
), respectively, along with ground-based ...optical photometry and spectroscopy and near-infrared spectroscopy of supernova SN 2017erp. The optical light curves and spectra are consistent with a normal SN Ia. Compared to previous photometric samples in the near-ultraviolet (NUV), SN 2017erp has UV colors that are redder than NUV-blue SNe Ia corrected to similar optical colors. The chromatic difference between SNe 2011fe and 2017erp is dominated by the intrinsic differences in the UV rather than the expected dust reddening. This chromatic difference is similar to the SALT2 color law, derived from rest-frame ultraviolet photometry of higher redshift SNe Ia. Differentiating between intrinsic UV diversity and dust reddening can have important consequences for determining cosmological distances with rest-frame ultraviolet photometry. This ultraviolet spectroscopic series is the first from
HST
of a normal, albeit reddened, NUV-red SN Ia and is important for analyzing SNe Ia with intrinsically redder NUV colors. We show model comparisons suggesting that metallicity could be the physical difference between NUV-blue and NUV-red SNe Ia, with emission peaks from reverse fluorescence near 3000 Å implying a factor of ∼10 higher metallicity in the upper layers of SN 2017erp compared to SN 2011fe. Metallicity estimates are very model dependent, however, and there are multiple effects in the UV. Further models and UV spectra of SNe Ia are needed to explore the diversity of SNe Ia, which show seemingly independent differences in the near-UV peaks and mid-UV flux levels.
Abstract
We present the 30 minutes cadence Kepler/K2 light curve of the Type Ia supernova (SN Ia) SN 2018agk, covering approximately one week before explosion, the full rise phase, and the decline ...until 40 days after peak. We additionally present ground-based observations in multiple bands within the same time range, including the 1 day cadence DECam observations within the first ∼5 days after the first light. The Kepler early light curve is fully consistent with a single power-law rise, without evidence of any bump feature. We compare SN 2018agk with a sample of other SNe Ia without early excess flux from the literature. We find that SNe Ia without excess flux have slowly evolving early colors in a narrow range (
g
−
i
≈ −0.20 ± 0.20 mag) within the first ∼10 days. On the other hand, among SNe Ia detected with excess, SN 2017cbv and SN 2018oh tend to be bluer, while iPTF16abc’s evolution is similar to normal SNe Ia without excess in
g
−
i
. We further compare the Kepler light curve of SN 2018agk with companion-interaction models, and rule out the existence of a typical nondegenerate companion undergoing Roche lobe overflow at viewing angles smaller than 45°.
SN 2016gkg is a nearby SN IIb discovered shortly after explosion. Like several other Type IIb events with early-time data, SN 2016gkg displays a double-peaked light curve, with the first peak ...associated with the cooling of a low-mass extended progenitor envelope. We present unprecedented intranight-cadence multi-band photometric coverage of the first light curve peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite, and various amateur-operated telescopes. Fitting these data to analytical shock-cooling models gives a progenitor radius of ∼40-150 with ∼2-40 × 10−2 of material in the extended envelope (depending on the model and the assumed host-galaxy extinction). Our radius estimates are broadly consistent with values derived independently (in other works) from HST imaging of the progenitor star. However, the shock-cooling model radii are on the lower end of the values indicated by pre-explosion imaging. Hydrodynamical simulations could refine the progenitor parameters deduced from the shock-cooling emission and test the analytical models.
Abstract
Hydrogen-rich, core-collapse supernovae are typically divided into four classes: IIP, IIL, IIn, and IIb. Recent hydrodynamic modelling shows that circumstellar material is required to ...produce the early light curves of most IIP/IIL supernovae. In this scenario, IIL supernovae experience large amounts of mass-loss before exploding. We test this hypothesis on ASASSN-15oz, a Type IIL supernova. With extensive follow-up in the X-ray, UV, optical, IR, and radio, we present our search for signs of interaction and the mass-loss history indicated by their detection. We find evidence of short-lived intense mass-loss just prior to explosion from light-curve modelling, amounting in 1.5 M⊙ of material within 1800 R⊙ of the progenitor. We also detect the supernova in the radio, indicating mass-loss rates of 10−6 to 10−7 M⊙ yr−1 prior to the extreme mass-loss period. Our failure to detect the supernova in the X-ray and the lack of narrow emission lines in the UV, optical, and NIR do not contradict this picture and place an upper limit on the mass-loss rate outside the extreme period of <10−4 M⊙ yr−1. This paper highlights the importance gathering comprehensive data on more Type II supernovae to enable detailed modelling of the progenitor and supernova which can elucidate their mass-loss histories and envelope structures and thus inform stellar evolution models.
Abstract
SN 2018aoz is a Type Ia SN with a
B
-band plateau and excess emission in infant-phase light curves ≲1 day after the 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 that the SN is intermediate between two subtypes of normal Type Ia: core normal and broad line. The excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on H
α
and He
i
favor 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
disfavors 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 1D models are incompatible with the infant-phase excess emission,
B
max
–
V
max
color, and weak strength 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 to be normal after ∼1 day.
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