416 research outputs found
Evidence for Cosmic Acceleration is Robust to Observed Correlations Between Type Ia Supernova Luminosity and Stellar Age
Type Ia Supernovae (SNe Ia) are powerful standardizable candles for
constraining cosmological models and provided the first evidence of the
accelerated expansion of the universe. Their precision derives from empirical
correlations, now measured from SNe Ia, between their luminosities,
light-curve shapes, colors and most recently with the stellar mass of their
host galaxy. As mass correlates with other galaxy properties, alternative
parameters have been investigated to improve SN Ia standardization though none
have been shown to significantly alter the determination of cosmological
parameters. We re-examine a recent claim, based on 34 SN Ia in nearby passive
host galaxies, of a 0.05 mag/Gyr dependence of standardized SN Ia luminosity on
host age which if extrapolated to higher redshifts, would be a bias up to 0.25
mag, challenging the inference of dark energy. We reanalyze this sample of
hosts using both the original method and a Bayesian hierarchical model and find
after a fuller accounting of the uncertainties the significance of a dependence
on age to be and after the removal of a single
poorly-sampled SN Ia. To test the claim that a trend seen in old stellar
populations can be applied to younger ages, we extend our analysis to a larger
sample which includes young hosts. We find the residual dependence of host age
(after all standardization typically employed for cosmological measurements) to
be consistent with zero for 254 SNe Ia from the Pantheon sample, ruling out the
large but low significance trend seen in passive hosts.Comment: 9 pages, 3 figures, 3 tables. Accepted for publication in ApJ
Propagating Uncertainties in the SALT3 Model Training Process to Cosmological Constraints
Type Ia supernovae (SNe Ia) are standardizable candles that must be modeled
empirically to yield cosmological constraints. To understand the robustness of
this modeling to variations in the model training procedure, we build an
end-to-end pipeline to test the recently developed SALT3 model. We explore the
consequences of removing pre-2000s low- or poorly calibrated -band data,
adjusting the amount and fidelity of SN Ia spectra, and using a
model-independent framework to simulate the training data. We find the SALT3
model surfaces are improved by having additional spectra and -band data, and
can be shifted by if host galaxy contamination is not sufficiently
removed from SN spectra. We find that resulting measurements of are
consistent to within for all training variants explored in this work,
with the largest shifts coming from variants that add color-dependent
calibration offsets or host galaxy contamination to the training spectra, and
those that remove pre-2000s low- data. These results demonstrate that the
SALT3 model training procedure is largely robust to reasonable variations in
the training data, but that additional attention must be paid to the treatment
of spectroscopic data in the training process. We also find that the training
procedure is sensitive to the color distributions of the input data; the
resulting measurement can be biased by if the color distribution
is not sufficiently wide. Future low- data, particularly -band
observations and high signal-to-noise ratio SN Ia spectra, will help to
significantly improve SN Ia modeling in the coming years.Comment: 16 pages, 10 figure
Improved constraints on H0 from a combined analysis of gravitational-wave and electromagnetic emission from GW170817
The luminosity distance measurement of GW170817 derived from GW analysis in
Abbott et al. 2017 (here, A17:H0) is highly correlated with the measured
inclination of the NS-NS system. To improve the precision of the distance
measurement, we attempt to constrain the inclination by modeling the broad-band
X-ray-to-radio emission from GW170817, which is dominated by the interaction of
the jet with the environment. We update our previous analysis and we consider
the radio and X-ray data obtained at days since merger. We find that the
afterglow emission from GW170817 is consistent with an off-axis relativistic
jet with energy
propagating into an environment with density , with preference for wider jets (opening angle
deg). For these jets, our modeling indicates an off-axis angle deg. We combine our constraints on with the
joint distance-inclination constraint from LIGO. Using the same
km/sec peculiar velocity uncertainty assumed in A17:H0 but with an inclination
constraint from the afterglow data, we get a value of \mbox{km/s/Mpc}, which is higher than the value of
\mbox{km/s/Mpc} found in A17:H0. Further,
using a more realistic peculiar velocity uncertainty of 250 km/sec derived from
previous work, we find km/s/Mpc for H0 from
this system. We note that this is in modestly better agreement with the local
distance ladder than the Planck CMB, though a significant such discrimination
will require such events. Future measurements at days of the
X-ray and radio emission will lead to tighter constraints.Comment: Submitted to ApJL. Comments Welcome. Revised uncertainties in v
Type Ia Supernova cosmology combining data from the mission and the Vera C. Rubin Observatory
The mission will provide first-of-its-kind coverage in the
near-infrared over deep (three fields, 10-20 square degrees each) and
wide (10000 square degrees) fields. While the survey is not designed to
discover transients, the deep fields will have repeated observations over a
two-week span, followed by a gap of roughly six months. In this analysis, we
explore how useful the deep field observations will be for measuring properties
of Type Ia supernovae (SNe Ia). Using simulations that include 's
planned depth, area and cadence in the deep fields, we calculate that more than
3700 SNe between will have at least five detections around
peak with signal-to-noise ratio larger than 3. While on their own,
light curves are not good enough to directly constrain distances, when combined
with LSST deep field observations, we find that uncertainties on SN distances
are reduced by 20-30% for . Furthermore, we
predict how well additional mock data can be used to constrain a key
systematic in SN Ia studies - the size of the luminosity 'step' found between
SNe hosted in high mass () and low mass () galaxies. This measurement has unique information in the rest-frame
NIR. We predict that if the step is caused by dust, we will be able to measure
its reduction in the NIR compared to optical at the 4 level. We
highlight that the LSST and observing strategies used in this work are
still provisional and some level of joint processing is required. Still, these
first results are promising, and assuming begins observations well
before the Nancy Roman Space Telescope (Roman), we expect this dataset to be
extremely helpful for preparation for Roman itself
Zooming In on the Progenitors of Superluminous Supernovae With the HST
We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the
host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including
11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the
superb angular resolution of HST, we characterize the galaxies' morphological
properties, sizes and star formation rate (SFR) densities. We determine the
supernova (SN) locations within the host galaxies through precise astrometric
matching, and measure physical and host-normalized offsets, as well as the SN
positions within the cumulative distribution of UV light pixel brightness. We
find that the host galaxies of H-poor SLSNe are irregular, compact dwarf
galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR
densities are high ( ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe
form in overdense environments. Their locations trace the UV light of their
host galaxies, with a distribution intermediate between that of long-duration
gamma-ray bursts (LGRBs) (which are strongly clustered on the brightest regions
of their hosts) and a uniform distribution (characteristic of normal
core-collapse SNe), though cannot be statistically distinguished from either
with the current sample size. Taken together, this strengthens the picture that
SLSN progenitors require different conditions than those of ordinary
core-collapse SNe to form, and that they explode in broadly similar galaxies as
do LGRBs. If the tendency for SLSNe to be less clustered on the brightest
regions than are LGRBs is confirmed by a larger sample, this would indicate a
different, potentially lower-mass progenitor for SLSNe than LRGBs.Comment: ApJ in press; matches published version. Minor changes following
referee's comments; conclusions unchange
GALEX Detection of Shock Breakout in Type II-P Supernova PS1-13arp: Implications for the Progenitor Star Wind
We present the GALEX detection of a UV burst at the time of explosion of an
optically normal Type II-P supernova (PS1-13arp) from the Pan-STARRS1 survey at
z=0.1665. The temperature and luminosity of the UV burst match the theoretical
predictions for shock breakout in a red supergiant, but with a duration a
factor of ~50 longer than expected. We compare the light curve of
PS1-13arp to previous GALEX detections of Type IIP SNe, and find clear
distinctions that indicate that the UV emission is powered by shock breakout,
and not by the subsequent cooling envelope emission previously detected in
these systems. We interpret the ~ 1 d duration of the UV signal with a shock
breakout in the wind of a red supergiant with a pre-explosion mass-loss rate of
~ 10^-3 Msun yr^-1. This mass-loss rate is enough to prolong the duration of
the shock breakout signal, but not enough to produce an excess in the optical
plateau light curve or narrow emission lines powered by circumstellar
interaction. This detection of non-standard, potentially episodic high
mass-loss in a RSG SN progenitor has favorable consequences for the prospects
of future wide-field UV surveys to detect shock breakout directly in these
systems, and provide a sensitive probe of the pre-explosion conditions of SN
progenitors.Comment: Accepted for Publication in Ap
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