81 research outputs found
Determining the Type, Redshift, and Phase of a Supernova Spectrum
We present an algorithm to identify the types of supernova spectra, and
determine their redshift and phase. This algorithm, based on the correlation
techniques of Tonry & Davis, is implemented in the SuperNova IDentification
code (SNID). It is used by members of the ESSENCE project to determine whether
a noisy spectrum of a high-redshift supernova is indeed of type Ia, as opposed
to, e.g., type Ib/c. Furthermore, by comparing the correlation redshifts
obtained using SNID with those determined from narrow lines in the supernova
host galaxy spectrum, we show that accurate redshifts (with a typical error <
0.01) can be determined for SNe Ia for which a spectrum of the host galaxy is
unavailable. Last, the phase of an input spectrum is determined with a typical
accuracy of ~3 days.Comment: 10 pages, 7 figures. To appear in "The Multicoloured Landscape of
Compact Objects and their Explosive Progenitors: Theory vs Observations"
(Cefalu, Sicily, June 2006). Eds. L. Burderi et al. (New York: AIP
A one-dimensional Chandrasekhar-mass delayed-detonation model for the broad-lined Type Ia supernova 2002bo
We present 1D non-local thermodynamic equilibrium (non-LTE) time-dependent
radiative-transfer simulations of a Chandrasekhar-mass delayed-detonation model
which synthesizes 0.51 Msun of 56Ni, and confront our results to the Type Ia
supernova (SN Ia) 2002bo over the first 100 days of its evolution. Assuming
only homologous expansion, this same model reproduces the bolometric and
multi-band light curves, the secondary near-infrared (NIR) maxima, and the
optical and NIR spectra. The chemical stratification of our model qualitatively
agrees with previous inferences by Stehle et al., but reveals significant
quantitative differences for both iron-group and intermediate-mass elements. We
show that +/-0.1 Msun (i.e., +/-20 per cent) variations in 56Ni mass have a
modest impact on the bolometric and colour evolution of our model. One notable
exception is the U-band, where a larger abundance of iron-group elements
results in less opaque ejecta through ionization effects, our model with more
56Ni displaying a higher near-UV flux level. In the NIR range, such variations
in 56Ni mass affect the timing of the secondary maxima but not their magnitude,
in agreement with observational results. Moreover, the variation in the I, J,
and K_s magnitudes is less than 0.1 mag within ~10 days from bolometric
maximum, confirming the potential of NIR photometry of SNe Ia for cosmology.
Overall, the delayed-detonation mechanism in single Chandrasekhar-mass white
dwarf progenitors seems well suited for SN 2002bo and similar SNe Ia displaying
a broad Si II 6355 A line. Whatever multidimensional processes are at play
during the explosion leading to these events, they must conspire to produce an
ejecta comparable to our spherically-symmetric model.Comment: Accepted for publication in MNRAS. The hydrodynamical input and
synthetic spectra are available at https://www-n.oca.eu/supernova/home.html .
Minor changes from v1: corrected several typos and updated acknowledgement
Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation
The faster light-curve evolution of low-luminosity Type Ia supernovae (SNe
Ia) suggests that they could result from the explosion of white dwarf (WD)
progenitors below the Chandrasekhar mass (). Here we present 1D
non-LTE time-dependent radiative transfer simulations of pure central
detonations of carbon-oxygen WDs with a mass (M_\rm{tot}) between 0.88
M and 1.15 M, and a yield between 0.08
M and 0.84 M. Their lower ejecta density compared to
models results in a more rapid increase of the luminosity at early
times and an enhanced -ray escape fraction past maximum light.
Consequently, their bolometric light curves display shorter rise times and
larger post-maximum decline rates. Moreover, the higher
M(^{56}\rm{Ni})/M_\rm{tot} ratio at a given mass enhances the
temperature and ionization level in the spectrum-formation region for the less
luminous models, giving rise to bluer colours at maximum light and a faster
post-maximum evolution of the colour. For sub- models fainter
than mag at peak, the greater bolometric decline and faster
colour evolution lead to a larger -band post-maximum decline rate, . In particular, all of our previously-published models
(standard and pulsational delayed detonations) are confined to mag, while the sub- models with
M_\rm{tot}\lesssim 1 M extend beyond this limit to mag for a peak mag, in better agreement
with the observed width-luminosity relation (WLR). Regardless of the precise
ignition mechanism, these simulations suggest that fast-declining SNe Ia at the
faint end of the WLR could result from the explosion of WDs whose mass is
significantly below the Chandrasekhar limit.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
Radiative Properties of Pair-instability Supernova Explosions
We present non-LTE time-dependent radiative-transfer simulations of
pair-instability supernovae (PISNe) stemming from red-supergiant (RSG),
blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born
in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties
in convection and stellar mass-loss rates, our initial conditions come from
physically-consistent models that treat evolution from the main-sequence, the
onset of the pair-production instability, and the explosion phase. With our set
of input models characterized by large 56Ni and ejecta masses, and large
kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar,
and Ib/c light-curve morphologies, although they have larger peak bolometric
luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss
the spectral properties for each model during the photospheric and nebular
phases, including Balmer lines in II-P and II-pec at early times, the dominance
of lines from intermediate-mass-elements (IMEs) near the bolometric maximum,
and the strengthening of metal line blanketing thereafter. Having similar
He-core properties, all models exhibit similar post-peak spectra that are
strongly blanketed by FeII and FeI lines, characterized by red colors, and that
arise from photospheres/ejecta with a temperature of <4000K. Combined with the
modest line widths after bolometric peak, these properties contrast with those
of known super-luminous SNe suggesting that PISNe are yet to be discovered.
Being reddish, PISNe will be difficult to observe at high redshift except when
they stem from RSG explosions, in which case they could be used as metallicity
probes and distance indicators.Comment: accepted to MNRA
Stable nickel production in Type Ia supernovae: A smoking gun for the progenitor mass?
At present, there are strong indications that white dwarf (WD) stars with
masses well below the Chandrasekhar limit (MCh ~ 1.4 Msun) contribute a
significant fraction of SN Ia progenitors. The relative fraction of stable
iron-group elements synthesized in the explosion has been suggested as a
possible discriminant between MCh and sub-MCh events. In particular, it is
thought that the higher-density ejecta of MCh WDs, which favours the synthesis
of stable isotopes of nickel, results in prominent [Ni II] lines in late-time
spectra. We study the explosive nucleosynthesis of stable nickel in SNe Ia
resulting from MCh and sub-MCh progenitors. We explore the potential for lines
of [Ni II] at 7378 \AA\ and 1.94 microns in late-time spectra to serve as a
diagnostic of the exploding WD mass, using nonlocal thermodynamic equilibrium
radiative-transfer simulations with the CMFGEN code. We find that the radiative
proton-capture reaction 57Co(p,gamma)58Ni is the dominant production mode for
58Ni in both MCh and sub-MCh models, while the alpha-capture reaction on 54Fe
has a negligible impact on the final 58Ni yield. More importantly, we
demonstrate that the lack of [Ni II] lines in late-time spectra of sub-MCh
events is not always due to an under-abundance of stable Ni; rather, it results
from the higher ionization of Ni in the inner ejecta. Conversely, the strong
[Ni II] lines predicted in our 1D MCh models are completely suppressed when
56Ni is sufficiently mixed with the innermost layers, which are rich in stable
iron-group elements. [Ni II] lines in late-time SN Ia spectra have a complex
dependency on the abundance of stable Ni, which limits their use in
distinguishing among MCh and sub-MCh progenitors. However, we argue that a
low-luminosity SN Ia displaying strong [Ni II] lines would most likely result
from a Chandrasekhar-mass progenitor. [Abridged]Comment: Accepted for publication in A&A, replaced with accepted version (+
corrected a typo in the conclusions: "overabundance" replaced with "over
abundance"). 20 pages, 10 figures. Model spectra available at
https://zenodo.org/record/552808
Family dispute: do Type IIP supernova siblings agree on their distance?
Context: Type II supernovae provide a direct way to estimate distances
through the expanding photosphere method, which is independent of the cosmic
distance ladder. A recently introduced Gaussian process-based method allows for
a fast and precise modelling of spectral time series, which puts accurate and
computationally cheap Type II-based absolute distance determinations within
reach.
Aims: The goal of the paper is to assess the internal consistency of this new
modelling technique coupled with the distance estimation empirically, using the
spectral time series of supernova siblings, i.e. supernovae that exploded in
the same host galaxy.
Methods: We use a recently developed spectral emulator code, which is trained
on \textsc{Tardis} radiative transfer models and is capable of a fast maximum
likelihood parameter estimation and spectral fitting. After calculating the
relevant physical parameters of supernovae we apply the expanding photosphere
method to estimate their distances. Finally, we test the consistency of the
obtained values by applying the formalism of Bayes factors.
Results: The distances to four different host galaxies were estimated based
on two supernovae in each. The distance estimates are not only consistent
within the errors for each of the supernova sibling pairs, but in the case of
two hosts they are precise to better than 5\%.
Conclusions: Even though the literature data we used was not tailored for the
requirements of our analysis, the agreement of the final estimates shows that
the method is robust and is capable of inferring both precise and consistent
distances. By using high-quality spectral time series, this method can provide
precise distance estimates independent of the distance ladder, which are of
high value for cosmology.Comment: 20 pages, 20 figures, 6 tables, Accepted in A&
Towards More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere
Motivated by the recognition that variation in the optical transmission of
the atmosphere is probably the main limitation to the precision of ground-based
CCD measurements of celestial fluxes, we review the physical processes that
attenuate the passage of light through the Earth's atmosphere. The next
generation of astronomical surveys, such as PanSTARRS and LSST, will greatly
benefit from dedicated apparatus to obtain atmospheric transmission data that
can be associated with each survey image. We review and compare various
approaches to this measurement problem, including photometry, spectroscopy, and
LIDAR. In conjunction with careful measurements of instrumental throughput,
atmospheric transmission measurements should allow next-generation imaging
surveys to produce photometry of unprecedented precision. Our primary concerns
are the real-time determination of aerosol scattering and absorption by water
along the line of sight, both of which can vary over the course of a night's
observations.Comment: 41 pages, 14 figures. Accepted PAS
Lightcurves of Type Ia Supernovae from Near the Time of Explosion
We present a set of 11 type Ia supernova (SN Ia) lightcurves with dense,
pre-maximum sampling. These supernovae (SNe), in galaxies behind the Large
Magellanic Cloud (LMC), were discovered by the SuperMACHO survey. The SNe span
a redshift range of z = 0.11 - 0.35. Our lightcurves contain some of the
earliest pre-maximum observations of SNe Ia to date. We also give a functional
model that describes the SN Ia lightcurve shape (in our VR-band). Our function
uses the "expanding fireball" model of Goldhaber et al. (1998) to describe the
rising lightcurve immediately after explosion but constrains it to smoothly
join the remainder of the lightcurve. We fit this model to a composite observed
VR-band lightcurve of three SNe between redshifts of 0.135 to 0.165. These SNe
have not been K-corrected or adjusted to account for reddening. In this
redshift range, the observed VR-band most closely matches the rest frame
V-band. Using the best fit to our functional description of the lightcurve, we
find the time between explosion and observed VR-band maximum to be
17.6+-1.3(stat)+-0.07(sys) rest-frame days for a SN Ia with a VR-band Delta
m_{-10} of 0.52mag. For the redshifts sampled, the observed VR-band
time-of-maximum brightness should be the same as the rest-frame V-band maximum
to within 1.1 rest-frame days.Comment: 35 pages, 18 figures, 15 tables; Higher quality PDF available at
http://ctiokw.ctio.noao.edu/~sm/sm/SNrise/index.html; AJ accepte
The Multi-Epoch Nearby Cluster Survey: type Ia supernova rate measurement in z~0.1 clusters and the late-time delay time distribution
We describe the Multi-Epoch Nearby Cluster Survey (MENeaCS), designed to
measure the cluster Type Ia supernova (SN Ia) rate in a sample of 57 X-ray
selected galaxy clusters, with redshifts of 0.05 < z < 0.15. Utilizing our real
time analysis pipeline, we spectroscopically confirmed twenty-three cluster SN
Ia, four of which were intracluster events. Using our deep CFHT/Megacam
imaging, we measured total stellar luminosities in each of our galaxy clusters,
and we performed detailed supernova detection efficiency simulations. Bringing
these ingredients together, we measure an overall cluster SN Ia rate within
R_{200} (1 Mpc) of 0.042^{+0.012}_{-0.010}^{+0.010}_{-0.008} SNuM
(0.049^{+0.016}_{-0.014}^{+0.005}_{-0.004} SNuM) and a SN Ia rate within red
sequence galaxies of 0.041^{+0.015}_{-0.015}^{+0.005}_{-0.010} SNuM
(0.041^{+0.019}_{-0.015}^{+0.005}_{-0.004} SNuM). The red sequence SN Ia rate
is consistent with published rates in early type/elliptical galaxies in the
`field'. Using our red sequence SN Ia rate, and other cluster SNe measurements
in early type galaxies up to , we derive the late time (>2 Gyr) delay
time distribution (DTD) of SN Ia assuming a cluster early type galaxy star
formation epoch of z_f=3. Assuming a power law form for the DTD, \Psi(t)\propto
t^s, we find s=-1.62\pm0.54. This result is consistent with predictions for the
double degenerate SN Ia progenitor scenario (s\sim-1), and is also in line with
recent calculations for the double detonation explosion mechanism (s\sim-2).
The most recent calculations of the single degenerate scenario delay time
distribution predicts an order of magnitude drop off in SN Ia rate \sim 6-7 Gyr
after stellar formation, and the observed cluster rates cannot rule this out.Comment: 35 pages, 14 figures, ApJ accepte
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