846 research outputs found
Rates and Progenitors of Type Ia Supernovae
The remarkable uniformity of Type Ia supernovae (SNe Ia) has allowed
astronomers to use them as distance indicators to measure the properties and
expansion history of the Universe. However, SNe Ia exhibit intrinsic variation
in both their spectra and observed brightness. To reduce these systematic
uncertainties, we need a deeper understanding of the observed variations in SNe
Ia. Toward this end, the Nearby Supernova Factory (SNfactory) has been designed
to discover hundreds of SNe Ia in a systematic and automated fashion and study
them in detail.
A prototype run of the SNfactory search pipeline conducted from 2002 to 2003
discovered 83 SNe at a final rate of 12 SNe/month. A large, homogeneous search
of this scale offers an excellent opportunity to measure the rate of SNe Ia.
This dissertation presents a new method for analyzing the true sensitivity of a
multi-epoch supernova search and finds a SN Ia rate from --0.1 of
SNe Ia/yr/Mpc from a preliminary
analysis of a subsample of the SNfactory prototype search.
Several unusual supernovae were found in the course of the SNfactory
prototype search. One in particular, SN 2002ic, was the first SN Ia to exhibit
convincing evidence for a circumstellar medium and offers valuable insight into
the progenitors of SNe Ia.Comment: Ph.D. Dissertation, Dept. of Physics, UC Berkeley, 2004. You may find
a nice version with full-resolution figures at either
http://supernova.lbl.gov/~wwoodvas/Papers/ or
http://www.cfa.harvard.edu/~wmwood-vasey/Papers
Dark energy FRW cosmology - dynamical system reconstruction
We develop a simple method of dark energy reconstruction using a geometrical
form of the luminosity-distance relation. In this method the FRW dynamical
system with dark energy is reconstructed instead of the equation of state
parameter. We give several examples which illustrate the usefulness of our
method in fitting the redshift transition from the decelerating to accelerating
phase as the value of the Hubble function at the transition.Comment: Talk presented at Spanish Relativity Meeting 2007, Puerto de la Cruz,
Tenerife, Spain, 10-14 September 200
Photometry of SN 2002ic and Implications for the Progenitor Mass-Loss History
We present new pre-maximum and late-time optical photometry of the Type
Ia/IIn supernova 2002ic. These observations are combined with the published
V-band magnitudes of Hamuy et al. (2003) and the VLT spectrophotometry of Wang
et al. (2004) to construct the most extensive light curve to date of this
unusual supernova. The observed flux at late time is significantly higher
relative to the flux at maximum than that of any other observed Type Ia
supernova and continues to fade very slowly a year after explosion. Our
analysis of the light curve suggests that a non-Type Ia supernova component
becomes prominent days after explosion. Modeling of the non-Type Ia
supernova component as heating from the shock interaction of the supernova
ejecta with pre-existing circumstellar material suggests the presence of a
cm gap or trough between the progenitor system and the
surrounding circumstellar material. This gap could be due to significantly
lower mass-loss years prior to explosion or
evacuation of the circumstellar material by a low-density fast wind. The latter
is consistent with observed properties of proto-planetary nebulae and with
models of white-dwarf + asymptotic giant branch star progenitor systems with
the asymptotic giant branch star in the proto-planetary nebula phase.Comment: accepted for publication in Ap
The Three Faces of Omega_m: Testing Gravity with Low and High Redshift SN Ia Surveys
Peculiar velocities of galaxies hosting Type Ia supernovae generate a
significant systematic effect in deriving the dark energy equation of state w,
at level of a few percent. Here we illustrate how the peculiar velocity effect
in SN Ia data can be turned from a 'systematic' into a probe of cosmological
parameters. We assume a flat Lambda-Cold Dark Matter model (w=-1) and use low
and high redshift SN Ia data to derive simultaneously three distinct estimates
of the matter density Omega_m which appear in the problem: from the geometry,
from the dynamics and from the shape of the matter power spectrum. We find that
each of the three Omega_m's agree with the canonical value Omega_m=0.25 to
within 1 sigma, for reasonably assumed fluctuation amplitude and Hubble
parameter. This is consistent with the standard cosmological scenario for both
the geometry and the growth of structure. For fixed Omega_m = 0.25 for all
three Omega_m's, we constrain gamma = 0.72 +/- 0.21 in the growth factor
Omega_m(z)^gamma, so we cannot currently distinguish between standard Einstein
gravity and predictions from some modified gravity models. Future surveys of
thousands of SN Ia, or inclusion of peculiar velocity data, could significantly
improve the above tests.Comment: accepted for publication in MNRAS (Letters), 5 pages, 4 figures.
Small changes to improve the text and the figures. Some further discussion, 1
equation and 1 reference adde
SweetSpot: Near-Infrared Observations of Thirteen Type Ia Supernovae from a New NOAO Survey Probing the Nearby Smooth Hubble Flow
We present 13 Type Ia supernovae (SNe Ia) observed in the restframe
near-infrared (NIR) from 0.02 < z < 0.09 with the WIYN High-resolution Infrared
Camera (WHIRC) on the WIYN 3.5-m telescope. With only 1-3 points per light
curve and a prior on the time of maximum from the spectrum used to type the
object we measure an H-band dispersion of spectroscopically normal SNe Ia of
0.164 mag. These observations continue to demonstrate the improved standard
brightness of SNe Ia in H-band even with limited data. Our sample includes two
SNe Ia at z ~ 0.09, which represent the most distant restframe NIR H-band
observations published to date.
This modest sample of 13 NIR SNe Ia represent the pilot sample for
"SweetSpot" - a three-year NOAO Survey program that will observe 144 SNe Ia in
the smooth Hubble flow. By the end of the survey we will have measured the
relative distance to a redshift of z ~ 0.05 to 1%. Nearby Type Ia supernova (SN
Ia) observations such as these will test the standard nature of SNe Ia in the
restframe NIR, allow insight into the nature of dust, and provide a critical
anchor for future cosmological SN Ia surveys at higher redshift.Comment: 36 pages, 8 figures, Submitted to Ap
Novae as a Mechanism for Producing Cavities around the Progenitors of SN 2002ic and Other SNe Ia
We propose that a nova shell ejected from a recurrent nova progenitor system
created the evacuated region around the explosion center of SN 2002ic. In this
picture, periodic shell ejections due to nova explosions on a white dwarf sweep
up the slow wind from the binary companion, creating density variations and
instabilities that lead to structure in the circumstellar medium (CSM). Our
model naturally explains the observed gap between the supernova explosion
center and the CSM in SN 2002ic, accounts for the density variations observed
in the CSM, and resolves the coincidence problem of the timing of the explosion
of SN 2002ic with respect to the apparent cessation of mass-loss in the
progenitor system. We also consider such nova outburst sweeping as a generic
feature of Type Ia supernovae with recurrent nova progenitors.Comment: Accepted to ApJL. 11 pages, 1 tabl
Type Ia Supernova Light Curve Inference: Hierarchical Bayesian Analysis in the Near Infrared
We present a comprehensive statistical analysis of the properties of Type Ia
SN light curves in the near infrared using recent data from PAIRITEL and the
literature. We construct a hierarchical Bayesian framework, incorporating
several uncertainties including photometric error, peculiar velocities, dust
extinction and intrinsic variations, for coherent statistical inference. SN Ia
light curve inferences are drawn from the global posterior probability of
parameters describing both individual supernovae and the population conditioned
on the entire SN Ia NIR dataset. The logical structure of the hierarchical
model is represented by a directed acyclic graph. Fully Bayesian analysis of
the model and data is enabled by an efficient MCMC algorithm exploiting the
conditional structure using Gibbs sampling. We apply this framework to the
JHK_s SN Ia light curve data. A new light curve model captures the observed
J-band light curve shape variations. The intrinsic variances in peak absolute
magnitudes are: sigma(M_J) = 0.17 +/- 0.03, sigma(M_H) = 0.11 +/- 0.03, and
sigma(M_Ks) = 0.19 +/- 0.04. We describe the first quantitative evidence for
correlations between the NIR absolute magnitudes and J-band light curve shapes,
and demonstrate their utility for distance estimation. The average residual in
the Hubble diagram for the training set SN at cz > 2000 km/s is 0.10 mag. The
new application of bootstrap cross-validation to SN Ia light curve inference
tests the sensitivity of the model fit to the finite sample and estimates the
prediction error at 0.15 mag. These results demonstrate that SN Ia NIR light
curves are as effective as optical light curves, and, because they are less
vulnerable to dust absorption, they have great potential as precise and
accurate cosmological distance indicators.Comment: 24 pages, 15 figures, 4 tables. Accepted for publication in ApJ.
Corrected typo, added references, minor edit
Gamma-ray burst contributions to constraining the evolution of dark energy
We explore the gamma-ray bursts' (GRBs') contributions in constraining the
dark energy equation of state (EOS) at high () and at middle
redshifts () and estimate how many GRBs are needed to get
substantial constraints at high redshifts. We estimate the constraints with
mock GRBs and mock type Ia supernovae (SNe Ia) for comparisons. When
constraining the dark energy EOS in a certain redshift range, we allow the dark
energy EOS parameter to vary only in that redshift bin and fix EOS parameters
elsewhere to -1. We find that it is difficult to constrain the dark energy EOS
beyond the redshifts of SNe Ia with GRBs unless some new luminosity relations
for GRBs with smaller scatters are discovered. However, at middle redshifts,
GRBs have comparable contributions with SNe Ia in constraining the dark energy
EOS.Comment: 3 pages, 5 figures. Published in Astronomy and Astrophysics.
Corrected referenc
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