799 research outputs found
Abundance stratification in Type Ia supernovae - V. SN 1986G bridging the gap between normal and subluminous SNe Ia
A detailed spectroscopic analysis of SN 1986G has been performed. SN 1986G
`bridges the gap' between normal and sub luminous type Ia supernova (SNe Ia).
The abundance tomography technique is used to determine the abundance
distribution of the elements in the ejecta. SN 1986G was found to be a low
energy Chandrasekhar mass explosion. Its kinetic energy was 70% of the standard
W7 model (0.9x10erg). Oxygen dominates the ejecta from the outermost
layers down to 9000kms , intermediate mass elements (IME) dominate
from 9000kms to 3500kms with Ni and Fe dominating
the inner layers 3500kms. The final masses of the main elements
in the ejecta were found to be, O=0.33M, IME=0.69M, stable NSE=0.21M,
Ni=0.14M. An upper limit of the carbon mass is set at C=0.02M. The
spectra of SN1986G consist of almost exclusively singly ionised species.
SN1986G can be thought of as a low luminosity extension of the main population
of SN Ia, with a large deflagration phase that produced more IMEs than a
standard SN Ia.Comment: Accepted for publication in MNRAS, update
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
Spectral Consequences of Deviation from Spherical Composition Symmetry in Type Ia Supernovae
We investigate the prospects for constraining the maximum scale of clumping
in composition that is consistent with observed Type Ia supernova flux spectra.
Synthetic spectra generated without purely spherical composition symmetry
indicate that gross asymmetries make prominent changes to absorption features.
Motivated by this, we consider the case of a single unblended line forming in
an atmosphere with perturbations of different scales and spatial distributions.
Perturbations of about 1% of the area of the photodisk simply weaken the
absorption feature by the same amount independent of the line of sight.
Conversely, perturbations of about 10% of the area of the photodisk introduce
variation in the absorption depth which does depend on the line of sight. Thus,
1% photodisk area perturbations may be consistent with observed profile
homogeneity but 10% photodisk area perturbations can not. Based on this, we
suggest that the absence of significant variation in the depths of Si II 6355
absorption features in normal Type Ia spectra near maximum light indicates that
any composition perturbations in these events are quite small. This also
constrains future three-dimensional explosion models to produce ejecta profiles
with only small scale inhomogeneities.Comment: 11 pages, 6 figure
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
Breaking the color-reddening degeneracy in type Ia supernovae
A new method to study the intrinsic color and luminosity of type Ia
supernovae (SNe Ia) is presented. A metric space built using principal
component analysis (PCA) on spectral series SNe Ia between -12.5 and +17.5 days
from B maximum is used as a set of predictors. This metric space is built to be
insensitive to reddening. Hence, it does not predict the part of color excess
due to dust-extinction. At the same time, the rich variability of SN Ia spectra
is a good predictor of a large fraction of the intrinsic color variability.
Such metric space is a good predictor of the epoch when the maximum in the B-V
color curve is reached. Multivariate Partial Least Square (PLS) regression
predicts the intrinsic B band light-curve and the intrinsic B-V color curve up
to a month after maximum. This allows to study the relation between the light
curves of SNe Ia and their spectra. The total-to-selective extinction ratio RV
in the host-galaxy of SNe Ia is found, on average, to be consistent with
typical Milky-Way values. This analysis shows the importance of collecting
spectra to study SNe Ia, even with large sample publicly available. Future
automated surveys as LSST will provide a large number of light curves. The
analysis shows that observing accompaning spectra for a significative number of
SNe will be important even in the case of "normal" SNe Ia.Comment: 11 pages, 11 figure
Optical studies of SN 2009jf: A type Ib supernova with an extremely slow decline and aspherical signature
Optical photometry and medium resolution spectroscopy of the type Ib
supernova SN 2009jf, during the period to +250days with respect to
the maximum are reported. The light curves are broad, with an extremely
slow decline. The early post-maximum decline rate in the band is similar to
SN 2008D, however, the late phase decline rate is slower than other studied
type Ib supernovae. With an absolute magnitude of
magnitude at peak, SN 2009jf is a normally bright supernova. The peak
bolometric luminosity and the energy deposition rate via Ni
Co chain indicate that
M of Ni was ejected during the explosion. He\,I 5876 \AA\ line
is clearly identified in the first spectrum of day , at a velocity of
km sec. The [O\,I] 6300-6364 \AA\ line seen in the nebular
spectrum has a multi-peaked and asymmetric emission profile, with the blue peak
being stronger. The estimated flux in this line implies \ga 1.34 M
oxygen was ejected. The slow evolution of the light curves of SN 2009jf
indicates the presence of a massive ejecta. The high expansion velocity in the
early phase and broader emission lines during the nebular phase suggest it to
be an explosion with a large kinetic energy. A simple qualitative estimate
leads to the ejecta mass of M M, and kinetic energy
E erg. The ejected mass estimate is indicative
of an initial main-sequence mass of \ga 20- 25 M.Comment: 14 pages, 13 figures; accepted for publication in MNRA
Spectra of supernovae in the nebular phase
When supernovae enter the nebular phase after a few months, they reveal
spectral fingerprints of their deep interiors, glowing by radioactivity
produced in the explosion. We are given a unique opportunity to see what an
exploded star looks like inside. The line profiles and luminosities encode
information about physical conditions, explosive and hydrostatic
nucleosynthesis, and ejecta morphology, which link to the progenitor properties
and the explosion mechanism. Here, the fundamental properties of spectral
formation of supernovae in the nebular phase are reviewed. The formalism
between ejecta morphology and line profile shapes is derived, including effects
of scattering and absorption. Line luminosity expressions are derived in
various physical limits, with examples of applications from the literature. The
physical processes at work in the supernova ejecta, including gamma-ray
deposition, non-thermal electron degradation, ionization and excitation, and
radiative transfer are described and linked to the computation and application
of advanced spectral models. Some of the results derived so far from
nebular-phase supernova analysis are discussed.Comment: Book chapter for 'Handbook of Supernovae,' edited by Alsabti and
Murdin, Springer. 51 pages, 14 figure
X-Ray, UV, and Optical Observations of Supernova 2006bp with Swift: Detection of Early X-Ray Emission
We present results on the X-ray and optical/UV emission from the type IIP SN
2006bp and the interaction of the SN shock with its environment, obtained with
the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on-board the Swift
observatory. SN 2006bp is detected in X-rays at a 4.5 sigma level of
significance in the merged XRT data from days 1 to 12 after the explosion. If
the X-ray luminosity of (1.8+/-0.4)E39 ergs/s is caused by interaction of the
SN shock with circumstellar material (CSM), deposited by a stellar wind from
the progenitor's companion star, a mass-loss rate of ~E-05 M_sun/yr is
inferred. The mass-loss rate is consistent with the non-detection in the radio
with the VLA on days 2, 9, and 11 after the explosion and characteristic of a
red supergiant progenitor with a mass around 12-15 M_sun prior to the
explosion. In combination with a follow-up XMM-Newton observation obtained on
day 21 after the explosion, an X-ray rate of decline with index 1.2+/-0.6 is
inferred. Since no other SN has been detected in X-rays prior to the optical
peak and since type IIP SNe have an extended 'plateau' phase in the optical, we
discuss the scenario that the X-rays might be due to inverse Compton scattering
of photospheric optical photons off relativistic electrons produced in
circumstellar shocks. However, due to the high required value of the Lorentz
factor (~10-100) we conclude that Inverse Compton scattering is an unlikely
explanation for the observed X-ray emission. The fast evolution of the
optical/ultraviolet spectral energy distribution and the spectral changes
observed with Swift reveal the onset of metal line-blanketing and cooling of
the expanding photosphere during the first few weeks after the outburst.Comment: 8 pages, 5 figures, accepted for publication in Ap
Two Type Ic supernovae in low-metallicity, dwarf galaxies: diversity of explosions
We present BVRI photometry and optical spectroscopy of two Type Ic supernovae
SN 2007bg and SN 2007bi discovered in wide-field, non-targeted surveys and
associated with sub-luminous blue dwarf galaxies. Neither SNe 2007bg nor 2007bi
were found in association with an observed GRB, but are found to inhabit
similar low-metallicity environments as GRB associated supernovae. The
radio-bright SN 2007bg is hosted by an extremely sub-luminous galaxy of
magnitude MB = -12.4+/-0.6 mag with an estimated oxygen abundance of
12+log(O/H) = 8.18+/-0.17. The lightcurve of SN 2007bg displays one of the
fastest post-maximum decline rates of all broad-lined Type Ic supernovae known
to date and, when combined with its high expansion velocities, a high kinetic
energy to ejected mass ratio (E_K/Mej ~ 2.7). We show that SN 2007bi is
possibly the most luminous Type Ic known, reaching a peak magnitude of MR ~
21.3 mag and displays a remarkably slow decline, following the radioactive
decay rate of 56Co to 56Fe throughout the course of its observed lifetime. From
a simple model of the bolometric light curve of SN 2007bi we estimate a total
ejected 56Ni mass of M_Ni = 3.5 - 4.5 solar masses, the largest 56Ni mass
measured in the ejecta of a supernova to date. There are two models that could
explain the high luminosity and large ejected 56Ni mass. One is a
pair-instability supernova (PISN) which has been predicted to occur for massive
stars at low metallicities. We measure the host galaxy metallicity of SN 2007bi
to be 12 + log(O/H) = 8.15+/-0.15 which is somewhat high to be consistent with
the PISN model. An alternative is the core-collapse of a C+O star of 20 - 40
solar masses which is the core of a star of originally 50 - 100 solar masses.
(Abridged)Comment: Minor changes. 19 pages, 21 Figures. Accepted by A&
Photometric and spectroscopic observations, and abundance tomography modelling of the Type Ia supernova SN 2014J located in M82
Spectroscopic and photometric observations of the nearby Type Ia Supernova (SN Ia) SN 2014J are presented. Spectroscopic observations were taken −8 to +10 d relative to Bband maximum, using FRODOSpec, a multipurpose integral-field unit spectrograph. The observations range from 3900 to 9000 Å. SN 2014J is located in M82 which makes it the
closest SN Ia studied in at least the last 28 yr. It is a spectroscopically normal SN Ia with high-velocity features.Wemodel the spectra of SN 2014J with a Monte Carlo radiative transfer code, using the abundance tomography technique. SN 2014J is highly reddened, with a host
galaxy extinction of E(B − V) = 1.2 (RV = 1.38). It has a �m15(B) of 1.08 ± 0.03 when corrected for extinction. As SN 2014J is a normal SN Ia, the density structure of the classical W7 model was selected. The model and photometric luminosities are both consistent with B-band maximum occurring on JD 245 6690.4 ± 0.12. The abundance of the SN 2014J behaves like other normal SN Ia, with significant amounts of silicon (12 per cent by mass)and sulphur (9 per cent by mass) at high velocities (12 300 km s−1) and the low-velocity ejecta (v < 6500 km s−1) consists almost entirely of 56Ni.
Key words: radiative transfer – techniques: spectroscopic – supernovae: general – supernovae: individual: SN 2014J
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