425 research outputs found
How Many Kilonovae Can Be Found in Past, Present, and Future Survey Data Sets?
The discovery of a kilonova (KN) associated with the Advanced LIGO (aLIGO)/Virgo event GW170817 opens up new avenues of multi-messenger astrophysics. Here, using realistic simulations, we provide estimates of the number of KNe that could be found in data from past, present, and future surveys without a gravitational-wave trigger. For the simulation, we construct a spectral time-series model based on the DES-GW multi-band light curve from the single known KN event, and we use an average of BNS rates from past studies of 10^3 Gpc^(-3) yr^(-1), consistent with the one event found so far. Examining past and current data sets from transient surveys, the number of KNe we expect to find for ASAS-SN, SDSS, PS1, SNLS, DES, and SMT is between 0 and 0.3. We predict the number of detections per future survey to be 8.3 from ATLAS, 10.6 from ZTF, 5.5/69 from LSST (the Deep Drilling/Wide Fast Deep), and 16.0 from WFIRST. The maximum redshift of KNe discovered for each survey is z = 0.8 for WFIRST, z = 0.25 for LSST, and z = 0.04 for ZTF and ATLAS. This maximum redshift for WFIRST is well beyond the sensitivity of aLIGO and some future GW missions. For the LSST survey, we also provide contamination estimates from Type Ia and core-collapse supernovae: after light curve and template-matching requirements, we estimate a background of just two events. More broadly, we stress that future transient surveys should consider how to optimize their search strategies to improve their detection efficiency and to consider similar analyses for GW follow-up programs
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
How Many Kilonovae Can Be Found in Past, Present, and Future Survey Data Sets?
The discovery of a kilonova (KN) associated with the Advanced LIGO (aLIGO)/Virgo event GW170817 opens up new avenues of multi-messenger astrophysics. Here, using realistic simulations, we provide estimates of the number of KNe that could be found in data from past, present, and future surveys without a gravitational-wave trigger. For the simulation, we construct a spectral time-series model based on the DES-GW multi-band light curve from the single known KN event, and we use an average of BNS rates from past studies of 10^3 Gpc^(-3) yr^(-1), consistent with the one event found so far. Examining past and current data sets from transient surveys, the number of KNe we expect to find for ASAS-SN, SDSS, PS1, SNLS, DES, and SMT is between 0 and 0.3. We predict the number of detections per future survey to be 8.3 from ATLAS, 10.6 from ZTF, 5.5/69 from LSST (the Deep Drilling/Wide Fast Deep), and 16.0 from WFIRST. The maximum redshift of KNe discovered for each survey is z = 0.8 for WFIRST, z = 0.25 for LSST, and z = 0.04 for ZTF and ATLAS. This maximum redshift for WFIRST is well beyond the sensitivity of aLIGO and some future GW missions. For the LSST survey, we also provide contamination estimates from Type Ia and core-collapse supernovae: after light curve and template-matching requirements, we estimate a background of just two events. More broadly, we stress that future transient surveys should consider how to optimize their search strategies to improve their detection efficiency and to consider similar analyses for GW follow-up programs
Cosmological model insensitivity of local from the Cepheid distance ladder
The observed tension ( difference) between the local distance
ladder measurement of the Hubble constant, , and its value inferred from
the cosmic microwave background (CMB) could hint at new, exotic, cosmological
physics. We test the impact of the assumption about the expansion history of
the universe () on the local distance ladder estimate of . In
the fiducial analysis, the Hubble flow Type Ia supernova (SN~Ia) sample is
truncated to and the deceleration parameter () fixed to -0.55.
We create realistic simulations of the calibrator and Pantheon samples and
account for a full systematics covariance between these two sets. We fit
several physically motivated dark energy models and derive combined constraints
from calibrator and Pantheon SNe~Ia and simultaneously infer and dark
energy properties. We find that the assumption on the dark energy model does
not significantly change the local distance ladder value of , with a
maximum difference () between the inferred value for different
models of 0.47 km s Mpc , i.e. a 0.6 shift in ,
significantly smaller than the observed tension. Additional freedom in the dark
energy models does not increase the error in the inferred value of .
Including systematics covariance between the calibrators, low redshift SNe, and
high redshift SNe can induce small shifts in the inferred value for . The
SN~Ia systematics in this study contribute to the total
uncertainty on .Comment: 11 pages, 3 figures, accepted to Ap
Prospects for resolving the Hubble constant tension with standard sirens
The Hubble constant () estimated from the local Cepheid-supernova (SN) distance ladder is in 3- tension with the value extrapolated from cosmic microwave background (CMB) data assuming the standard cosmological model. Whether this tension represents new physics or systematic effects is the subject of intense debate. Here, we investigate how new, independent estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (PPD). We show that, with existing data, the inverse distance ladder formed from BOSS baryon acoustic oscillation measurements and the Pantheon SN sample yields an posterior near-identical to the Planck CMB measurement. The observed local distance ladder value is a very unlikely draw from the resulting PPD. Turning to the future, we find that a sample of binary neutron star "standard sirens" (detectable within the next decade) will be able to adjudicate between the local and CMB estimates
eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
During its two year prime mission the Transiting Exoplanet Survey Satellite
(TESS) will perform a time-series photometric survey covering over 80% of the
sky. This survey comprises observations of 26 24 x 96 degree sectors that are
each monitored continuously for approximately 27 days. The main goal of TESS is
to find transiting planets around 200,000 pre-selected stars for which fixed
aperture photometry is recorded every two minutes. However, TESS is also
recording and delivering Full-Frame Images (FFIs) of each detector at a 30
minute cadence. We have created an open-source tool, eleanor, to produce light
curves for objects in the TESS FFIs. Here, we describe the methods used in
eleanor to produce light curves that are optimized for planet searches. The
tool performs background subtraction, aperture and PSF photometry,
decorrelation of instrument systematics, and cotrending using principal
component analysis. We recover known transiting exoplanets in the FFIs to
validate the pipeline and perform a limited search for new planet candidates in
Sector 1. Our tests indicate that eleanor produces light curves with
significantly less scatter than other tools that have been used in the
literature. Cadence-stacked images, and raw and detrended eleanor light curves
for each analyzed star will be hosted on MAST, with planet candidates on
ExoFOP-TESS as Community TESS Objects of Interest (CTOIs). This work confirms
the promise that the TESS FFIs will enable the detection of thousands of new
exoplanets and a broad range of time domain astrophysics.Comment: 21 pages, 13 figures, 2 tables, Accepted to PAS
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
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