Abstract
SN 2017dio shows both spectral characteristics of a type-Ic supernova (SN) and signs of a hydrogen-rich circumstellar medium (CSM). Prominent, narrow emission lines of H and He are ...superposed on the continuum. Subsequent evolution revealed that the SN ejecta are interacting with the CSM. The initial SN Ic identification was confirmed by removing the CSM interaction component from the spectrum and comparing with known SNe Ic and, reversely, adding a CSM interaction component to the spectra of known SNe Ic and comparing them to SN 2017dio. Excellent agreement was obtained with both procedures, reinforcing the SN Ic classification. The light curve constrains the pre-interaction SN Ic peak absolute magnitude to be around
M
g
=
−
17.6
mag. No evidence of significant extinction is found, ruling out a brighter luminosity required by an SN Ia classification. These pieces of evidence support the view that SN 2017dio is an SN Ic, and therefore the first firm case of an SN Ic with signatures of hydrogen-rich CSM in the early spectrum. The CSM is unlikely to have been shaped by steady-state stellar winds. The mass loss of the progenitor star must have been intense,
M
˙
∼
0.02
(
ϵ
H
α
/
0.01
)
−
1
(
v
wind
/
500
km s
−1
)
(
v
shock
/
10,000 km s
−1
)
−3
M
⊙
yr
−1
, peaking at a few decades before the SN. Such a high mass-loss rate might have been experienced by the progenitor through eruptions or binary stripping.
A new class of ultra-long-duration (more than 10,000 seconds) γ-ray bursts has recently been suggested. They may originate in the explosion of stars with much larger radii than those producing normal ...long-duration γ-ray bursts or in the tidal disruption of a star. No clear supernova has yet been associated with an ultra-long-duration γ-ray burst. Here we report that a supernova (SN 2011kl) was associated with the ultra-long-duration γ-ray burst GRB 111209A, at a redshift z of 0.677. This supernova is more than three times more luminous than type Ic supernovae associated with long-duration γ-ray bursts, and its spectrum is distinctly different. The slope of the continuum resembles those of super-luminous supernovae, but extends further down into the rest-frame ultraviolet implying a low metal content. The light curve evolves much more rapidly than those of super-luminous supernovae. This combination of high luminosity and low metal-line opacity cannot be reconciled with typical type Ic supernovae, but can be reproduced by a model where extra energy is injected by a strongly magnetized neutron star (a magnetar), which has also been proposed as the explanation for super-luminous supernovae.
ABSTRACT
We present optical photometric and spectroscopic observations of the faint-and-fast evolving Type Iax supernova (SN) 2019gsc, extending from the time of g-band maximum until about 50 d ...post-maximum, when the object faded to an apparent r-band magnitude mr = 22.48 ± 0.11 mag. SN 2019gsc reached a peak luminosity of only Mg = −13.58 ± 0.15 mag, and is characterized with a post-maximum decline rate Δm15(g) = 1.08 ± 0.14 mag. These light curve parameters are comparable to those measured for SN 2008ha of Mg = −13.89 ± 0.14 mag at peak and Δm15(g) =1.80 ± 0.03 mag. The spectral features of SN 2019gsc also resemble those of SN 2008ha at similar phases. This includes both the extremely low ejecta velocity at maximum, ∼3000 km s−1, and at late-time (phase +54 d) strong forbidden iron and cobalt lines as well as both forbidden and permitted calcium features. Furthermore, akin to SN 2008ha, the bolometric light curve of SN 2019gsc is consistent with the production of ≈0.003 ± 0.001 M⊙ of 56Ni. The explosion parameters, Mej ≈ 0.13 M⊙ and Ek ≈ 12 × 1048 erg, are also similar to those inferred for SN 2008ha. We estimate a subsolar oxygen abundance for the host galaxy of SN 2019gsc (12 + log10(O/H) =8.10 ± 0.18 dex), consistent with the equally metal-poor environment of SN 2008ha. Altogether, our data set for SN 2019gsc indicates that this is a member of a small but growing group of extreme SN Iax that includes SN 2008ha and SN 2010ae.
Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a ..."normal" spiral galaxy (NGC 3191) in terms of stellar mass (several times 1010 M ) and metallicity (roughly solar). At redshift z = 0.031, Gaia17biu is also the lowest-redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I, while its peak luminosity (Mg = −21 mag) is substantially lower than that of Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the ∼0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with <5.4 × 1026 erg s−1 Hz−1 at 10 GHz, which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSN-I with known populations of gamma-ray-burst-like central engines.
Aims. We present a comprehensive dataset of optical and near-infrared photometry and spectroscopy of type Ia supernova (SN) 2016hnk, combined with integral field spectroscopy (IFS) of its host ...galaxy, MCG -01-06-070, and nearby environment. Our goal with this complete dataset is to understand the nature of this peculiar object. Methods. Properties of the SN local environment are characterized by means of single stellar population synthesis applied to IFS observations taken two years after the SN exploded. We performed detailed analyses of SN photometric data by studying its peculiar light and color curves. SN 2016hnk spectra were compared to other 1991bg-like SNe Ia, 2002es-like SNe Ia, and Ca-rich transients. In addition, we used abundance stratification modeling to identify the various spectral features in the early phase spectral sequence and also compared the dataset to a modified non-LTE model previously produced for the sublumnious SN 1999by. Results. SN 2016hnk is consistent with being a subluminous (MB = −16.7 mag, sBV=0.43 ± 0.03), highly reddened object. The IFS of its host galaxy reveals both a significant amount of dust at the SN location, residual star formation, and a high proportion of old stellar populations in the local environment compared to other locations in the galaxy, which favors an old progenitor for SN 2016hnk. Inspection of a nebular spectrum obtained one year after maximum contains two narrow emission lines attributed to the forbidden Ca II λλ7291,7324 doublet with a Doppler shift of 700 km s−1. Based on various observational diagnostics, we argue that the progenitor of SN 2016hnk was likely a near Chandrasekhar-mass (MCh) carbon-oxygen white dwarf that produced 0.108 M⊙ of 56Ni. Our modeling suggests that the narrow Ca II features observed in the nebular spectrum are associated with 48Ca from electron capture during the explosion, which is expected to occur only in white dwarfs that explode near or at the MCh limit.
Abstract
We present the results of an extensive observational campaign on the nearby Type Ibn SN 2015G, including data from radio through ultraviolet wavelengths. SN 2015G was asymmetric, showing ...late-time nebular lines redshifted by ∼1000 km s−1. It shared many features with the prototypical SN Ibn 2006jc, including extremely strong He i emission lines and a late-time blue pseudo-continuum. The young SN 2015G showed narrow P-Cygni profiles of He i, but never in its evolution did it show any signature of hydrogen – arguing for a dense, ionized and hydrogen-free circumstellar medium moving outward with a velocity of ∼1000 km s−1 and created by relatively recent mass-loss from the progenitor star. Ultraviolet through infrared observations show that the fading SN 2015G (which was probably discovered some 20 d post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. Archival HST images provide upper limits on the luminosity of SN 2015G's progenitor, while non-detections of any luminous radio afterglow and optical non-detections of outbursts over the past two decades provide constraints upon its mass-loss history.
We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of Mr = −17.98, a peak bolometric ...luminosity of ∼1.4 × 1043 erg s−1, and a rapid decline rate of 0.48 0.03 mag day−1 in the r band. The bolometric luminosity evolves too quickly to be explained by pure 56Ni heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of Mej = 0.10 0.05 M . Our spectral modeling suggests the ejecta is composed of intermediate mass elements including O, Si, and Mg and trace amounts of Fe-peak elements, which disfavors a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition, and high likelihood of additional powering-the core collapse of an ultra-stripped progenitor, the accretion induced collapse (AIC) of a white dwarf, and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favors either the AIC with magnetar powering or a white dwarf-neutron star merger with energy from disk wind shocks.
ABSTRACT
This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8 ± 0.9 d to reach a peak ...brightness of −19.70 ± 0.02 mag in the LSQgr band. Early spectra of LSQ13ddu showed the presence of weak and narrow $\mathrm{ He}\, {\small I}$ features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow $\mathrm{ He}\, {\small I}$ velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive 56Ni powering but can be explained through a combination of CSM interaction and an underlying 56Ni decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib.
Abstract
Using data from the Complete Nearby (redshift
z
host
< 0.02) sample of Type Ia Supernovae (CNIa0.02), we find a linear relation between two parameters derived from the
B
−
V
color curves of ...Type Ia supernovae: the
color stretch
s
BV
and the rising color slope
s
0
*
(
B
−
V
)
after the peak, and this relation applies to the full range of
s
BV
. The
s
BV
parameter is known to be tightly correlated with the peak luminosity, especially for
fast decliners
(dim Type Ia supernovae), and the luminosity correlation with
s
BV
is markedly better than with the classic light-curve width parameters such as Δ
m
15
(
B
). Thus, our new linear relation can be used to infer peak luminosity from
s
0
*
. Unlike
s
BV
(or Δ
m
15
(
B
)), the measurement of
s
0
*
(
B
−
V
)
does not rely on a well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.
Using data from the Complete Nearby (redshift z host < 0.02) sample of Type Ia Supernovae (CNIa0.02), we find a linear relation between two parameters derived from the B − V color curves of Type ...Ia supernovae: the color stretch s BV and the rising color slope s 0 * (B – V) after the peak, and this relation applies to the full range of s BV . The s BV parameter is known to be tightly correlated with the peak luminosity, especially for fast decliners (dim Type Ia supernovae), and the luminosity correlation with s BV is markedly better than with the classic light-curve width parameters such as Δm 15 (B). Thus, our new linear relation can be used to infer peak luminosity from s 0 * . Unlike s BV (or Δm 15 (B)), the measurement of s 0 * (B – V) does not rely on a well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.
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