53 research outputs found
LSQ13ddu: a rapidly evolving stripped-envelope supernova with early circumstellar interaction signatures
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 HeI 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 HeI 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
Chandra, HST/STIS, NICER, Swift, and TESS Detail the Flare Evolution of the Repeating Nuclear Transient ASASSN-14ko
ASASSN-14ko is a nuclear transient at the center of the AGN ESO 253-G003 that
undergoes periodic flares. Optical flares were first observed in 2014 by the
All-Sky Automated Survey for Supernovae (ASAS-SN) and their peak times are
well-modeled with a period of days and period derivative
of . Here we present ASAS-SN, Chandra, HST/STIS, NICER,
Swift, and TESS data for the flares that occurred in December 2020, April 2021,
July 2021, and November 2021. The HST/STIS UV spectra evolve from blue shifted
broad absorption features to red shifted broad emission features over 10
days. The Swift UV/optical light curves peaked as predicted by the timing
model, but the peak UV luminosities varied between flares and the UV flux in
July 2021 was roughly half the brightness of all other peaks. The X-ray
luminosities consistently decreased and the spectra became harder during the
UV/optical rise but apparently without changes in absorption. Finally, two
high-cadence TESS light curves from December 2020 and November 2018 showed that
the slopes during the rising and declining phases changed over time, which
indicates some stochasticity in the flare's driving mechanism. ASASSN-14ko
remains observationally consistent with a repeating partial tidal disruption
event, but, these rich multi-wavelength data are in need of a detailed
theoretical model.Comment: 25 pages, 14 figures, 4 tables; Submitted to ApJ, comments welcom
The carbon-rich type Ic supernova 2016adj in the iconic dust lane of Centaurus A: signatures of interaction with circumstellar hydrogen?
We present a comprehensive data set of supernova (SN) 2016adj located within
the central dust lane of Centaurus A. SN 2016adj is significantly reddened and
after correcting the peak apparent -band magnitude ()
for Milky Way reddening and our inferred host-galaxy reddening parameters
(i.e., and ), we estimate
it reached a peak absolute magnitude of . Detailed inspection of
the optical/NIR spectroscopic time-series reveals a carbon-rich SN Ic and not a
SN Ib/IIb as previously suggested in the literature. The NIR spectra shows
prevalent carbon-monoxide formation occurring already by +41 days past -band
maximum, which is days earlier than previously reported in the
literature for this object. Interestingly around two months past maximum, the
NIR spectrum of SN~2016adj begins to exhibit H features, with a +97~d medium
resolution spectrum revealing both Paschen and Bracket lines with absorption
minima of km/s, full-width-half-maximum emission velocities of
km/s, and emission line ratios consistent with a dense emission
region. We speculate these attributes are due to circumstellar interaction
(CSI) between the rapidly expanding SN ejecta and a H-rich shell of material
formed during the pre-SN phase. A bolometric light curve is constructed and a
semi-analytical model fit suggests the supernova synthesized 0.5 solar masses
of Ni and ejected 4.2 solar masses of material, though these values
should be approached with caution given the large uncertainties associated with
the adopted reddening parameters, possible CSI contamination, and known light
echo emission. Finally, inspection of Hubble Space Telescope archival data
yielded no progenitor detection.Comment: Submitted to A&A, comments are welcom
Serendipitous Nebular-phase JWST Imaging of SN Ia 2021aefx: Testing the Confinement of 56-Co Decay Energy
We present new 0.3-21 micron photometry of SN 2021aefx in the spiral galaxy
NGC 1566 at +357 days after B-band maximum, including the first detection of
any SN Ia at >15 micron. These observations follow earlier JWST observations of
SN 2021aefx at +255 days after the time of maximum brightness, allowing us to
probe the temporal evolution of the emission properties. We measure the
fraction of flux emerging at different wavelengths and its temporal evolution.
Additionally, the integrated 0.3-14 micron decay rate of mag/100 days is higher than the decline rate from the
radioactive decay of Co of mag/100 days. The most plausible
explanation for this discrepancy is that flux is shifting to >14 micron, and
future JWST observations of SNe Ia will be able to directly test this
hypothesis. However, models predicting non-radiative energy loss cannot be
excluded with the present data.Comment: Accepted for publication in ApJL; 11 pages, 4 figures, 2 tables in
two-column AASTEX63 forma
Revealing the progenitor of SN 2021zby through analysis of the shock-cooling light curve
We present early observations and analysis of the double-peaked Type IIb
supernova (SN IIb) 2021zby. captured the prominent early shock cooling
peak of SN 2021zby within the first 10 days after explosion with a
30-minute cadence. We present optical and near-infrared spectral series of SN
2021zby, including three spectra during the shock cooling phase. Using a
multi-band model fit, we find that the inferred properties of its progenitor
are consistent with a red supergiant or yellow supergiant, with an envelope
mass of 0.3-3.0 M and an envelope radius of 50-350. These inferred progenitor properties are similar to those of other
SNe IIb with double-peak feature, such as SNe 1993J, 2011dh, 2016gkg and
2017jgh. This study further validates the importance of the high cadence and
early coverage in resolving the shape of the shock cooling light curve, while
the multi-band observations, especially UV, is also necessary to fully
constrain the progenitor properties.Comment: 12 pages, 5 figures, 2 tables, submitted to ApJ
ASASSN-18am/SN 2018gk : An overluminous Type IIb supernova from a massive progenitor
ASASSN-18am/SN 2018gk is a newly discovered member of the rare group of
luminous, hydrogen-rich supernovae (SNe) with a peak absolute magnitude of mag that is in between normal core-collapse SNe and superluminous
SNe. These SNe show no prominent spectroscopic signatures of ejecta interacting
with circumstellar material (CSM), and their powering mechanism is debated.
ASASSN-18am declines extremely rapidly for a Type II SN, with a
photospheric-phase decline rate of . Owing to the
weakening of HI and the appearance of HeI in its later phases, ASASSN-18am is
spectroscopically a Type IIb SN with a partially stripped envelope. However,
its photometric and spectroscopic evolution show significant differences from
typical SNe IIb. Using a radiative diffusion model, we find that the light
curve requires a high synthesised mass and ejecta with high kinetic energy erg. Introducing a magnetar central engine still requires
and erg. The high
mass is consistent with strong iron-group nebular lines in its
spectra, which are also similar to several SNe Ic-BL with high
yields. The earliest spectrum shows "flash ionisation" features, from which we
estimate a mass-loss rate of . This wind density is too low to power the luminous light
curve by ejecta-CSM interaction. We measure expansion velocities as high as km/s for , which is remarkably high compared to other SNe
II. We estimate an oxygen core mass of using the [OI]
luminosity measured from a nebular-phase spectrum, implying a progenitor with a
zero-age main sequence mass of
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