6,176 research outputs found
Diversity of Decline-Rate-Corrected Type Ia Supernova Rise Times: One Mode or Two?
B-band light-curve rise times for eight unusually well-observed nearby Type
Ia supernovae (SNe) are fitted by a newly developed template-building
algorithm, using light-curve functions that are smooth, flexible, and free of
potential bias from externally derived templates and other prior assumptions.
From the available literature, photometric BVRI data collected over many
months, including the earliest points, are reconciled, combined, and fitted to
a unique time of explosion for each SN. On average, after they are corrected
for light-curve decline rate, three SNe rise in 18.81 +- 0.36 days, while five
SNe rise in 16.64 +- 0.21 days. If all eight SNe are sampled from a single
parent population (a hypothesis not favored by statistical tests), the rms
intrinsic scatter of the decline-rate-corrected SN rise time is 0.96 +0.52
-0.25 days -- a first measurement of this dispersion. The corresponding global
mean rise time is 17.44 +- 0.39 days, where the uncertainty is dominated by
intrinsic variance. This value is ~2 days shorter than two published averages
that nominally are twice as precise, though also based on small samples. When
comparing high-z to low-z SN luminosities for determining cosmological
parameters, bias can be introduced by use of a light-curve template with an
unrealistic rise time. If the period over which light curves are sampled
depends on z in a manner typical of current search and measurement strategies,
a two-day discrepancy in template rise time can bias the luminosity comparison
by ~0.03 magnitudes.Comment: As accepted by The Astrophysical Journal; 15 pages, 6 figures, 2
tables. Explanatory material rearranged and enhanced; Fig. 4 reformatte
The Risetime of Nearby Type Ia Supernovae
We present calibrated photometric measurements of the earliest detections of
nearby type Ia supernovae (SNe Ia). The set of ~30 new, unfiltered CCD
observations delineate the early rise behavior of SNe Ia > 18 to 10 days before
maximum. Using simple empirical models, we demonstrate the strong correlation
between the risetime (i.e., the time between explosion and maximum), the
post-rise light-curve shape, and the peak luminosity. Using a variety of
light-curve shape methods, we find the risetime to B maximum for a SN Ia with
Delta m15(B)=1.1 mag and peak M_V=-19.45 mag to be 19.5+/-0.2 days. We find
that the peak brightness of SNe Ia is correlated with their risetime; SNe Ia
which are 0.10 mag brighter at peak in the B-band require 0.80+/-0.05 days
longer to reach maximum light.
We determine the effects of several possible sources of systematic errors,
but none of these significantly impacts the inferred risetime. Constraints on
SN Ia progenitor systems and explosion models are derived from a comparison
between the observed and theoretical predictions of the risetime.Comment: Submitted to the Astronomical Journal, 24 pages, 7 figure
The Rise Times of High and Low Redshift Type Ia Supernovae are Consistent
We present a self-consistent comparison of the rise times for low- and
high-redshift Type Ia supernovae. Following previous studies, the early light
curve is modeled using a t-squared law, which is then mated with a modified
Leibundgut template light curve. The best-fit t-squared law is determined for
ensemble samples of low- and high-redshift supernovae by fitting simultaneously
for all light curve parameters for all supernovae in each sample. Our method
fully accounts for the non-negligible covariance amongst the light curve
fitting parameters, which previous analyses have neglected. Contrary to Riess
et al. (1999), we find fair to good agreement between the rise times of the
low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of
the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2
days statistical), making any search for evidence of evolution based on a
comparison of rise times premature. Furthermore, systematic effects on rise
time determinations from the high-redshift observations, due to the form of the
late-time light curve and the manner in which the light curves of these
supernovae were sampled, can bias the high-redshift rise time determinations by
up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for
cosmology - do not suffer any significant bias, nor any significant increase in
uncertainty.Comment: 18 pages, 4 figures, Accepted for publication in the Astronomical
Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were
corrected and a few sentences were added for improved clarit
A spectroscopically confirmed z=1.327 galaxy-scale deflector magnifying a z~8 Lyman-Break galaxy in the Brightest of Reionizing Galaxies survey
We present a detailed analysis of an individual case of gravitational lensing
of a Lyman-Break galaxy (LBG) in a blank field, identified in Hubble
Space Telescope imaging obtained as part of the Brightest of Reionizing
Galaxies survey. To investigate the close proximity of the bright
() -dropout to a small group of foreground galaxies, we
obtained deep spectroscopy of the dropout and two foreground galaxies using
VLT/X-Shooter. We detect H-, H-, [OIII] and [OII] emission in
the brightest two foreground galaxies (unresolved at the natural seeing of
arcsec), placing the pair at . We can rule out emission lines
contributing all of the observed broadband flux in band at
, allowing us to exclude the candidate as a low redshift
interloper with broadband photometry dominated by strong emission lines. The
foreground galaxy pair lies at the peak of the luminosity, redshift and
separation distributions for deflectors of strongly lensed objects,
and we make a marginal detection of a demagnified secondary image in the
deepest () filter. We show that the configuration can be accurately
modelled by a singular isothermal ellipsoidal deflector and a S\'{e}rsic source
magnified by a factor of . The reconstructed source in the
best-fitting model is consistent with luminosities and morphologies of
LBGs in the literature. The lens model yields a group mass of
and a stellar mass-to-light ratio for the
brightest deflector galaxy of within its effective radius. The foreground galaxies'
redshifts would make this one of the few strong lensing deflectors discovered
at .Comment: Accepted for publication in MNRAS. 16 pages, 11 figures, 3 table
The Impact of Strong Gravitational Lensing on Observed Lyman-Break Galaxy Numbers at 4<z<8 in the GOODS and the XDF Blank Fields
Detection of Lyman-Break Galaxies (LBGs) at high-redshift can be affected by
gravitational lensing induced by foreground deflectors not only in galaxy
clusters, but also in blank fields. We quantify the impact of strong
magnification in the samples of , , , LBGs () observed in the XDF and GOODS/CANDELS fields, by investigating the
proximity of dropouts to foreground objects. We find that of bright
LBGs () by
foreground objects. This fraction decreases from at to
at . Since the observed fraction of strongly lensed
galaxies is a function of the shape of the luminosity function (LF), it can be
used to derive Schechter parameters, and , independently
from galaxy number counts. Our magnification bias analysis yields
Schechter-function parameters in close agreement with those determined from
galaxy counts albeit with larger uncertainties. Extrapolation of our analysis
to suggests that future surveys with JSWT, WFIRST and EUCLID
should find excess LBGs at the bright-end, even if there is an intrinsic
exponential cutoff of number counts. Finally, we highlight how the
magnification bias measurement near the detection limit can be used as probe of
the population of galaxies too faint to be detected. Preliminary results using
this novel idea suggest that the magnification bias at is not
as strong as expected if extends well below the current
detection limits in the XDF. At face value this implies a flattening of the LF
at . However, selection effects and completeness estimates
are difficult to quantify precisely. Thus, we do not rule out a steep LF
extending to .Comment: Submitted to ApJ on 18/12/201
Galaxy Zoo Supernovae
This paper presents the first results from a new citizen science project:
Galaxy Zoo Supernovae. This proof of concept project uses members of the public
to identify supernova candidates from the latest generation of wide-field
imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and
scoring model, and demonstrate the effectiveness of this novel method using
imaging data and transients from the Palomar Transient Factory (PTF). We
examine the results collected over the period April-July 2010, during which
nearly 14,000 supernova candidates from PTF were classified by more than 2,500
individuals within a few hours of data collection. We compare the transients
selected by the citizen scientists to those identified by experienced PTF
scanners, and find the agreement to be remarkable - Galaxy Zoo Supernovae
performs comparably to the PTF scanners, and identified as transients 93% of
the ~130 spectroscopically confirmed SNe that PTF located during the trial
period (with no false positive identifications). Further analysis shows that
only a small fraction of the lowest signal-to-noise SN detections (r > 19.5)
are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with >
8{\sigma} detections in the PTF imaging data. The Galaxy Zoo Supernovae project
has direct applicability to future transient searches such as the Large
Synoptic Survey Telescope, by both rapidly identifying candidate transient
events, and via the training and improvement of existing machine classifier
algorithms.Comment: 13 pages, 10 figures, accepted MNRA
The Subluminous and Peculiar Type Ia Supernova PTF09dav
PTF09dav is a peculiar subluminous type Ia supernova (SN) discovered by the
Palomar Transient Factory (PTF). Spectroscopically, it appears superficially
similar to the class of subluminous SN1991bg-like SNe, but it has several
unusual features which make it stand out from this population. Its peak
luminosity is fainter than any previously discovered SN1991bg-like SN Ia (M_B
-15.5), but without the unusually red optical colors expected if the faint
luminosity were due to extinction. The photospheric optical spectra have very
unusual strong lines of Sc II and Mg I, with possible Sr II, together with
stronger than average Ti II and low velocities of ~6000 km/s. The host galaxy
of PTF09dav is ambiguous. The SN lies either on the extreme outskirts (~41kpc)
of a spiral galaxy, or in an very faint (M_R>-12.8) dwarf galaxy, unlike other
1991bg-like SNe which are invariably associated with massive, old stellar
populations. PTF09dav is also an outlier on the light-curve-width--luminosity
and color--luminosity relations derived for other sub-luminous SNe Ia. The
inferred 56Ni mass is small (0.019+/-0.003Msun), as is the estimated ejecta
mass of 0.36Msun. Taken together, these properties make PTF09dav a remarkable
event. We discuss various physical models that could explain PTF09dav. Helium
shell detonation or deflagration on the surface of a CO white-dwarf can explain
some of the features of PTF09dav, including the presence of Sc and the low
photospheric velocities, but the observed Si and Mg are not predicted to be
very abundant in these models. We conclude that no single model is currently
capable of explaining all of the observed signatures of PTF09dav.Comment: Accepted for publication in Ap
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
Initial Hubble Diagram Results from the Nearby Supernova Factory
The use of Type Ia supernovae as distance indicators led to the discovery of
the accelerating expansion of the universe a decade ago. Now that large second
generation surveys have significantly increased the size and quality of the
high-redshift sample, the cosmological constraints are limited by the currently
available sample of ~50 cosmologically useful nearby supernovae. The Nearby
Supernova Factory addresses this problem by discovering nearby supernovae and
observing their spectrophotometric time development. Our data sample includes
over 2400 spectra from spectral timeseries of 185 supernovae. This talk
presents results from a portion of this sample including a Hubble diagram
(relative distance vs. redshift) and a description of some analyses using this
rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008;
see v1 for full-length versio
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