686 research outputs found
Properties of Type II Plateau Supernova SNLS-04D2dc: Multicolor Light Curves of Shock Breakout and Plateau
Shock breakout is the brightest radiative phenomenon in a Type II supernova
(SN). Although it was predicted to be bright, the direct observation is
difficult due to the short duration and X-ray/ultraviolet-peaked spectra. First
entire observations of the shock breakouts of Type II Plateau SNe (SNe IIP)
were reported in 2008 by ultraviolet and optical observations by the {\it
GALEX} satellite and supernova legacy survey (SNLS), named SNLS-04D2dc and
SNLS-06D1jd. We present multicolor light curves of a SN IIP, including the
shock breakout and plateau, calculated with a multigroup radiation
hydrodynamical code {\sc STELLA} and an evolutionary progenitor model. The
synthetic multicolor light curves reproduce well the observations of
SNLS-04D2dc. This is the first study to reproduce the ultraviolet light curve
of the shock breakout and the optical light curve of the plateau consistently.
We conclude that SNLS-04D2dc is the explosion with a canonical explosion energy
ergs and that its progenitor is a star with a zero-age
main-sequence mass and a presupernova radius . The
model demonstrates that the peak apparent -band magnitude of the shock
breakout would be mag if a SN being identical to
SNLS-04D2dc occurs at a redshift , which can be reached by 8m-class
telescopes. The result evidences that the shock breakout has a great potential
to detect SNe IIP at z\gsim1.Comment: 5 pages, 5 figures. Accepted for publication in the Astrophysical
Journal Letter
Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
Observationally, supernovae (SNe) are divided into subclasses pertaining to
their distinct characteristics. This diversity reflects the diversity in the
progenitor stars. It is not entirely clear how different evolutionary paths
leading massive stars to become a SN are governed by fundamental parameters
such as progenitor initial mass and metallicity. This paper places constraints
on progenitor initial mass and metallicity in distinct core-collapse SN
subclasses, through a study of the parent stellar populations at the explosion
sites. Integral field spectroscopy (IFS) of 83 nearby SN explosion sites with a
median distance of 18 Mpc has been collected and analysed, enabling detection
and spectral extraction of the parent stellar population of SN progenitors.
From the parent stellar population spectrum, the initial mass and metallicity
of the coeval progenitor are derived by means of comparison to simple stellar
population models and strong-line methods. Additionally, near-infrared IFS was
employed to characterise the star formation history at the explosion sites. No
significant metallicity differences are observed among distinct SN types. The
typical progenitor mass is found to be highest for SN Ic, followed by type Ib,
then types IIb and II. SN IIn is the least associated with young stellar
populations and thus massive progenitors. However, statistically significant
differences in progenitor initial mass are observed only when comparing SNe IIn
with other subclasses. Stripped-envelope SN progenitors with initial mass
estimate lower than 25~ are found; these are thought to be the result
of binary progenitors. Confirming previous studies, these results support the
notion that core-collapse SN progenitors cannot arise from single-star channel
only, and both single and binary channels are at play in the production of
core-collapse SNe. [ABRIDGED]Comment: 18 pages, 10 figures, accepted to A&
Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South
Luminous AGNs are usually selected by their non-stellar colours or their
X-ray emission. Colour selection cannot be used to select low-luminosity AGNs,
since their emission is dominated by the host galaxy. Objects with low X-ray to
optical ratio escape even the deepest X-ray surveys performed so far. In a
previous study we presented a sample of candidates selected through optical
variability in the Chandra Deep Field South, where repeated optical
observations were performed for the STRESS supernova survey. We obtained new
optical spectroscopy for a sample of variability selected candidates with the
ESO NTT telescope. We analysed the new spectra, together with those existing in
the literature and studied the distribution of the objects in U-B and B-V
colours, optical and X-ray luminosity, and variability amplitude. A large
fraction (17/27) of the observed candidates are broad-line luminous AGNs,
confirming the efficiency of variability in detecting quasars. We detect: i)
extended objects which would have escaped the colour selection and ii) objects
of very low X-ray to optical ratio. Several objects resulted to be
narrow-emission line galaxies where variability indicates nuclear activity,
while no emission lines were detected in others. Some of these galaxies have
variability and X-ray to optical ratio close to active galactic nuclei, while
others have much lower variability and X-ray to optical ratio. This result can
be explained by the dilution of the nuclear light due to the host galaxy. Our
results demonstrate the effectiveness of supernova search programmes to detect
large samples of low-luminosity AGNs. A sizable fraction of the AGN in our
variability sample had escaped X-ray detection (5/47) and/or colour selection
(9/48). Spectroscopic follow-up to fainter flux limits is strongly encouraged.Comment: 14 pages, 11 figures, to appear in A&
Shock Breakout in Type II Plateau Supernovae: Prospects for High Redshift Supernova Surveys
Shock breakout is the brightest radiative phenomenon in a supernova (SN) but
is difficult to be observed owing to the short duration and X-ray/ultraviolet
(UV)-peaked spectra. After the first observation from the rising phase reported
in 2008, its observability at high redshift is attracting enormous attention.
We perform multigroup radiation hydrodynamics calculations of explosions for
evolutionary presupernova models with various main-sequence masses , metallicities , and explosion energies . We present multicolor
light curves of shock breakout in Type II plateau SNe, being the most frequent
core-collapse SNe, and predict apparent multicolor light curves of shock
breakout at various redshifts . We derive the observable SN rate and
reachable redshift as functions of filter and limiting magnitude by taking into account an initial mass function, cosmic star formation
history, intergalactic absorption, and host galaxy extinction. We propose a
realistic survey strategy optimized for shock breakout. For example, the
-band observable SN rate for mag is 3.3 SNe
degree day and a half of them locates at . It is clear
that the shock breakout is a beneficial clue to probe high- core-collapse
SNe. We also establish ways to identify shock breakout and constrain SN
properties from the observations of shock breakout, brightness, time scale, and
color. We emphasize that the multicolor observations in blue optical bands with
hour intervals, preferably over continuous nights, are essential
to efficiently detect, identify, and interpret shock breakout.Comment: 26 pages, 23 figures. Accepted for publication in the Astrophysical
Journal Supplement Serie
Large Polarization Degree of Comet 2P/Encke Continuum Based on Spectropolarimetric Signals During Its 2017 Apparition
Spectropolarimetry is a powerful technique for investigating the physical
properties of gas and solid materials in cometary comae without mutual
contamination, but there have been few spectropolarimetric studies to extract
each component. We attempt to derive the continuum polarization degree of comet
2P/Encke, free from influence of molecular emissions. The target is unique in
that it has an orbit dynamically decoupled from Jupiter like main-belt
asteroids, while ejecting gas and dust like ordinary comets. We observed the
comet using the Higashi-Hiroshima Optical and Near-Infrared Camera attached to
the Cassegrain focus of the 150-cm Kanata telescope on UT 2017 February 21 when
the comet was at the solar phase angle of 75.7 deg. We find that the continuum
polarization degree with respect to the scattering plane is 33.8+/-2.7 % at the
effective wavelength of 0.815 um, which is significantly higher than those of
cometary dust in a high-Pmax group at similar phase angles. Assuming that an
ensemble polarimetric response of 2P/Encke's dust as a function of phase angle
is morphologically similar with those of other comets, its maximum polarization
degree is estimated to > 40 % at the phase angle of ~100 deg. In addition, we
obtain the polarization degrees of the C2 swan bands (0.51-0.56 um), the NH2
alpha bands (0.62-0.69 um) and the CN-red system (0.78-0.94 um) in a range of
3-19 %, which depend on the molecular species and rotational quantum numbers of
each branch. The polarization vector aligns nearly perpendicularly to the
scattering plane with the average of 0.4 deg over a wavelength range of
0.50-0.97 um. From the observational evidence, we conjecture that the large
polarization degree of 2P/Encke would be attributable to a dominance of large
dust particles around the nucleus, which have remained after frequent
perihelion passages near the Sun.Comment: 9 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
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