1,201 research outputs found
The Outermost Ejecta of Type Ia Supernovae
The properties of the highest velocity ejecta of normal Type Ia supernovae
(SNe Ia) are studied via models of very early optical spectra of 6 SNe. At
epochs earlier than 1 week before maximum, SNe with a rapidly evolving Si II
6355 line velocity (HVG) have a larger photospheric velocity than SNe with a
slowly evolving Si II 6355 line velocity (LVG). Since the two groups have
comparable luminosities, the temperature at the photosphere is higher in LVG
SNe. This explains the different overall spectral appearance of HVG and LVG
SNe. However, the variation of the Ca II and Si II absorptions at the highest
velocities (v >~ 20,000 km/s) suggests that additional factors, such as
asphericity or different abundances in the progenitor white dwarf, affect the
outermost layers. The C II 6578 line is marginally detected in 3 LVG SNe,
suggesting that LVG undergo less intense burning. The carbon mass fraction is
small, only less than 0.01 near the photosphere, so that he mass of unburned C
is only <~ 0.01 Msun. Radioactive 56Ni and stable Fe are detected in both LVG
and HVG SNe. Different Fe-group abundances in the outer layers may be one of
the reasons for spectral diversity among SNe Ia at the earliest times. The
diversity among SNe Ia at the earliest phases could also indicate an intrinsic
dispersion in the width-luminosity relation of the light curve.Comment: 13 pages, 10 figures, Accepted for publication in The Astrophysical
Journa
Abundance stratification in Type Ia Supernovae - II: The rapidly declining, spectroscopically normal SN 2004eo
The variation of properties of Type Ia supernovae, the thermonuclear
explosions of Chandrasekhar-mass carbon-oxygen white dwarfs, is caused by
different nucleosynthetic outcomes of these explosions, which can be traced
from the distribution of abundances in the ejecta. The composition
stratification of the spectroscopically normal but rapidly declining SN2004eo
is studied performing spectrum synthesis of a time-series of spectra obtained
before and after maximum, and of one nebular spectrum obtained about eight
months later. Early-time spectra indicate that the outer ejecta are dominated
by oxygen and silicon, and contain other intermediate-mass elements (IME),
implying that the outer part of the star was subject only to partial burning.
In the inner part, nuclear statistical equilibrium (NSE) material dominates,
but the production of 56Ni was limited to ~0.43 \pm 0.05 Msun. An innermost
zone containing ~0.25 Msun of stable Fe-group material is also present. The
relatively small amount of NSE material synthesised by SN2004eo explains both
the dimness and the rapidly evolving light curve of this SN.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
The Type Ic Hypernova SN 2003dh/GRB 030329
The spectra of SN 2003dh, identified in the afterglow of GRB030329, are
modeled using radiation transport codes. It is shown that SN 2003dh had a high
explosion kinetic energy ( erg in spherical symmetry),
making it one of the most powerful hypernovae observed so far, and supporting
the case for association between hypernovae and Gamma Ray Bursts. However, the
light curve derived from fitting the spectra suggests that SN 2003dh was not as
bright as SN 1998bw, ejecting only \sim 0.35\Msun of \Nifs. The spectra of SN
2003dh resemble those of SN 1998bw around maximum, but later they look more
like those of the less energetic hypernova SN 1997ef. The spectra and the
inferred light curve can be modeled adopting a density distribution similar to
that used for SN 1998bw at \kms but more like that of SN 1997ef at
lower velocities. The mass of the ejecta is \sim 8\Msun, somewhat less than
in the other two hypernovae. The progenitor must have been a massive star (M
\sim 35-40\Msun), as for other hypernovae. The need to combine different
one-dimensional explosion models strongly indicates that SN 2003dh was an
asymmetric explosion.Comment: 11 pages, 1 table and 5 figures. To appear in the Astrophysical
Journal (Letters). Revised version taking referee's comments into account,
minor change
The nebular spectrum of the type Ia supernova 2003hv: evidence for a non-standard event
The optical and near-infrared late-time spectrum of the under-luminous Type
Ia supernova 2003hv is analysed with a code that computes nebular emission from
a supernova nebula. Synthetic spectra based on the classical explosion model W7
are unable to reproduce the large \FeIII/\FeII\ ratio and the low infrared flux
at year after explosion, although the optical spectrum of SN\,2003hv
is reproduced reasonably well for a supernova of luminosity intermediate
between normal and subluminous (SN\,1991bg-like) ones. A possible solution is
that the inner layers of the supernova ejecta (v \lsim 8000\,\kms) contain
less mass than predicted by classical explosion models like W7. If this inner
region contains \sim 0.5 \Msun of material, as opposed to \sim 0.9 \Msun in
Chandrasekhar-mass models developed within the Single Degenerate scenario, the
low density inhibits recombination, favouring the large \FeIII/\FeII\ ratio
observed in the optical, and decreases the flux in the \FeII\ lines which
dominate the IR spectrum. The most likely scenario may be an explosion of a
sub-Chandrasekhar mass white dwarf. Alternatively, the violent/dynamical merger
of two white dwarfs with combined mass exceeding the Chandrasekhar limit also
shows a reduced inner density.Comment: MNRAS, in pres
Subaru and Keck Observations of the Peculiar Type Ia Supernova 2006gz at Late Phases
Recently, a few peculiar Type Ia supernovae (SNe) that show exceptionally
large peak luminosity have been discovered. Their luminosity requires more than
1 Msun of 56Ni ejected during the explosion, suggesting that they might have
originated from super-Chandrasekhar mass white dwarfs. However, the nature of
these objects is not yet well understood. In particular, no data have been
taken at late phases, about one year after the explosion. We report on Subaru
and Keck optical spectroscopic and photometric observations of the SN Ia
2006gz, which had been classified as being one of these "overluminous" SNe Ia.
The late-time behavior is distinctly different from that of normal SNe Ia,
reinforcing the argument that SN 2006gz belongs to a different subclass than
normal SNe Ia. However, the peculiar features found at late times are not
readily connected to a large amount of 56Ni; the SN is faint, and it lacks [Fe
II] and [Fe III] emission. If the bulk of the radioactive energy escapes the SN
ejecta as visual light, as is the case in normal SNe Ia, the mass of 56Ni does
not exceed ~ 0.3 Msun. We discuss several possibilities to remedy the problem.
With the limited observations, however, we are unable to conclusively identify
which process is responsible. An interesting possibility is that the bulk of
the emission might be shifted to longer wavelengths, unlike the case in other
SNe Ia, which might be related to dense C-rich regions as indicated by the
early-phase data. Alternatively, it might be the case that SN 2006gz, though
peculiar, was actually not substantially overluminous at early times.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in The
Astrophysical Journa
The diversity of Type Ia Supernovae: evidence for systematics?
The photometric and spectroscopic properties of 26 well observed Type Ia
Supernovae (SNeIa) were analyzed with the aim to explore SNIa diversity. The
sample includes (Branch-)normal SNe as well as extreme events like SNe 1991T
and 1991bg, while the truly peculiar SNIa, SN2000cx and SN2002cx are not
included in our sample . A statistical treatment reveals the existence of three
different groups. The first group (FAINT) consists of faint SNeIa similar to
SN1991bg, with low expansion velocities and rapid evolution of SiII velocity. A
second group consists of ``normal'' SNeIa, also with high temporal velocity
gradient (HVG), but with brighter mean absolute magnitude =-19.3 and
higher expansion velocities than the FAINT SNe. The third group includes both
``normal'' and SN1991T-like SNeIa: these SNe populate a narrow strip in the
SiII velocity evolution plot, with a small velocity gradient (SVG), but have
absolute magnitudes similar to HVGs. While the FAINT and HVG SNeIa together
seem to define a relation between RSi(II) and Dm15(B), the SVG ones either do
not conform with that relation or define a new, looser one. The RSi(II)
pre-maximum evolution of HVGs is strikingly different from that of SVGs. The
impact of this evidence on the understanding of SNIa diversity, in terms of
explosion mechanisms, degree of ejecta mixing, and ejecta-CSM interaction, is
discussed.Comment: 9 pages, 3 figures, accepted for publication to ApJ; few referee's
comments adde
Detection of a light echo from SN1998bu
About 500d after explosion the light curve of the Type Ia SN1998bu suddenly
flattened and at the same time the spectrum changed from the typical nebular
emission to a blue continuum with broad absorption and emission features
reminiscent of the SN spectrum at early phases. We show that in analogy to
SN1991Tbu (Schmidt et al. 1994), this can be explained by the emergence of a
light echo from a foreground dust cloud. Based on a simple model we argue that
the amount of dust required can consistently explain the extinction which has
been estimated by completely independent methods. Because of the similar echo
luminosity but much higher optical depth of the dust in SN1998bu compared with
SN1991T, we expect that the echo ring size of SN1998bu grows faster than in
SN1991T. HST observations have indeed confirmed this prediction.Comment: 5 pages (including 3 figures) - Accepted for pubblication in ApJ
Letter
WISeREP - An Interactive Supernova Data Repository
We have entered an era of massive data sets in astronomy. In particular, the
number of supernova (SN) discoveries and classifications has substantially
increased over the years from few tens to thousands per year. It is no longer
the case that observations of a few prototypical events encapsulate most
spectroscopic information about SNe, motivating the development of modern tools
to collect, archive, organize and distribute spectra in general, and SN spectra
in particular. For this reason we have developed the Weizmann Interactive
Supernova data REPository - WISeREP - an SQL-based database (DB) with an
interactive web-based graphical interface. The system serves as an archive of
high quality SN spectra, including both historical (legacy) data as well as
data that is accumulated by ongoing modern programs. The archive provides
information about objects, their spectra, and related meta-data. Utilizing
interactive plots, we provide a graphical interface to visualize data, perform
line identification of the major relevant species, determine object redshifts,
classify SNe and measure expansion velocities. Guest users may view and
download spectra or other data that have been placed in the public domain.
Registered users may also view and download data that are proprietary to
specific programs with which they are associated. The DB currently holds >8000
spectra, of which >5000 are public; the latter include published spectra from
the Palomar Transient Factory, all of the SUSPECT archive, the
Caltech-Core-Collapse Program, the CfA SN spectra archive and published spectra
from the UC Berkeley SNDB repository. It offers an efficient and convenient way
to archive data and share it with colleagues, and we expect that data stored in
this way will be easy to access, increasing its visibility, usefulness and
scientific impact.Comment: To be published in PASP. WISeREP:
http://www.weizmann.ac.il/astrophysics/wiserep
On the progenitors of Type Ia supernovae
© 2018 Elsevier B.V. We review all the models proposed for the progenitor systems of Type Ia supernovae and discuss the strengths and weaknesses of each scenario when confronted with observations. We show that all scenarios encounter at least a few serious difficulties, if taken to represent a comprehensive model for the progenitors of all Type Ia supernovae (SNe Ia). Consequently, we tentatively conclude that there is probably more than one channel leading SNe Ia. While the single-degenerate scenario (in which a single white dwarf accretes mass from a normal stellar companion) has been studied in some detail, the other scenarios will need a similar level of scrutiny before any firm conclusions can be drawn
Luminosity distributions of Type Ia Supernovae
We have assembled a dataset of 165 low redshift, 0.06, publicly available type Ia supernovae (SNe Ia). We produce maximum light magnitude ( and ) distributions of SNe Ia to explore the diversity of parameter space that they can fill. Before correction for host galaxy extinction we find that the mean and of SNe Ia are mag and mag respectively. Host galaxy extinction is corrected using a new method based on the SN spectrum. After correction, the mean values of and of SNe Ia are and mag respectively. After correction for host galaxy extinction, `normal' SNeIa (mag) fill a larger parameter space in the Width-Luminosity Relation (WLR) than previously suggested, and there is evidence for luminous SNe Ia with large . We find a bimodal distribution in , with a pronounced lack of transitional events at =1.6 mag. We confirm that faster, low-luminosity SNe tend to come from passive galaxies. Dividing the sample by host galaxy type, SNe Ia from star-forming (S-F) galaxies have a mean mag, while SNe Ia from passive galaxies have a mean mag. Even excluding fast declining SNe, `normal' ( mag) SNe Ia from S-F and passive galaxies are distinct. In the -band, there is a difference of 0.40.13 mag between the median () values of the `normal' SN Ia population from passive and S-F galaxies. This is consistent with (10)% of `normal' SNe Ia from S-F galaxies coming from an old stellar population
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