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Metzger B.D.,Columbia Astrophysics Laboratory | Bauswein A.,Aristotle University of Thessaloniki | Goriely S.,Free University of Colombia | Kasen D.,Lawrence Berkeley National Laboratory | Kasen D.,University of California at Berkeley
Monthly Notices of the Royal Astronomical Society | Year: 2014

The merger of binary neutron stars (NSs) ejects a small quantity of neutron-rich matter, the radioactive decay of which powers a day to week long thermal transient known as a kilonova. Most of the ejecta remains sufficiently dense during its expansion that all neutrons are captured into nuclei during the r-process. However, recent general relativistic merger simulations by Bauswein and collaborators show that a small fraction of the ejected mass (a few per cent, or ~10-4 M⊙) expands sufficiently rapidly for most neutrons to avoid capture. This matter originates from the shocked-heated interface between the merging NSs. Here, we show that the β-decay of these free neutrons in the outermost ejecta powers a 'precursor' to the main kilonova emission, which peaks on a time-scale of ~ few hours following merger at U-band magnitude ~22 (for an assumed distance of 200 Mpc). The high luminosity and blue colours of the neutron precursor render it a potentially important counterpart to the gravitational wave source, that may encode valuable information on the properties of the merging binary (e.g. NS-NS versus NS-black hole) and the NS equation of state. Future work is necessary to assess the robustness of the fast-moving ejecta and the survival of free neutrons in the face of neutrino absorptions, although the precursor properties are robust to a moderate amount of leptonization. Our results provide additional motivation for short latency gravitational wave triggers and rapid follow-up searches with sensitive ground-based telescopes. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Jarosik N.,Princeton University | Bennett C.L.,Johns Hopkins University | Dunkley J.,University of Oxford | Gold B.,Johns Hopkins University | And 18 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

New full-sky temperature and polarization maps based on seven years of data from WMAP are presented. The new results are consistent with previous results, but have improved due to reduced noise from the additional integration time, improved knowledge of the instrument performance, and improved data analysis procedures. The improvements are described in detail. The seven-year data set is well fit by a minimal six-parameter flat ACDM model. The parameters for this model, using the WMAP data in conjunction with baryon acoustic oscillation data from the Sloan Digital Sky Survey and priors on H0 from Hubble Space Telescope observations, are Ωbh2 = 0.02260 ± 0.00053, Ωbh2 = 0.1123 ± 0.0035, Ω ∧ = 0.728+0.015 -0.016, ns = 0.963 ± 0.012, τ = 0.087 ± 0.014, and σ8 = 0.809 ± 0.024 (68% CL uncertainties). The temperature power spectrum signal-to-noise ratio per multipole is greater that unity for multipoles l ≲ 919, allowing a robust measurement of the third acoustic peak. This measurement results in improved constraints on the matter density, Ωmh2 = 0.1334+0.0056 -0.0055, and the epoch of matter-radiation equality, zeq = 3196 +134 -133-, using WMAP data alone. The new WMAP data, when combined with smaller angular scale microwave background anisotropy data, result in a 3a detection of the abundance of primordial helium, YHe = 0.326 ± 0.075. When combined with additional external data sets, the WMAP data also yield better determinations of the total mass of neutrinos, Σ m ν ≤ 0.58 eV (95% CL), and the effective number of neutrino species, iVeff = 4.34+0.86 0.88. The power-law index of the primordial power spectrum is now determined to be ns = 0.963 ± 0.012, excluding the Harrison-Zel'dovich-Peebles spectrum by >3σ. These new WMAP measurements provide important tests of big bang cosmology. © 2011. The American Astronomical Society. Source


Hinshaw G.,University of British Columbia | Larson D.,Johns Hopkins University | Komatsu E.,Max Planck Institute for Astrophysics | Komatsu E.,University of Tokyo | And 21 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

We present cosmological parameter constraints based on the final nine-year Wilkinson Microwave Anisotropy Probe (WMAP) data, in conjunction with a number of additional cosmological data sets. The WMAP data alone, and in combination, continue to be remarkably well fit by a six-parameter ΛCDM model. When WMAP data are combined with measurements of the high-l cosmic microwave background anisotropy, the baryon acoustic oscillation scale, and the Hubble constant, the matter and energy densities, Ωb h 2, Ωc h 2, and ΩΛ, are each determined to a precision of ∼1.5%. The amplitude of the primordial spectrum is measured to within 3%, and there is now evidence for a tilt in the primordial spectrum at the 5σ level, confirming the first detection of tilt based on the five-year WMAP data. At the end of the WMAP mission, the nine-year data decrease the allowable volume of the six-dimensional ΛCDM parameter space by a factor of 68,000 relative to pre-WMAP measurements. We investigate a number of data combinations and show that their ΛCDM parameter fits are consistent. New limits on deviations from the six-parameter model are presented, for example: the fractional contribution of tensor modes is limited to r < 0.13 (95% CL); the spatial curvature parameter is limited to ; the summed mass of neutrinos is limited to ∑m ν < 0.44 eV (95% CL); and the number of relativistic species is found to lie within N eff = 3.84 ± 0.40, when the full data are analyzed. The joint constraint on N eff and the primordial helium abundance, Y He, agrees with the prediction of standard big bang nucleosynthesis. We compare recent Planck measurements of the Sunyaev-Zel'dovich effect with our seven-year measurements, and show their mutual agreement. Our analysis of the polarization pattern around temperature extrema is updated. This confirms a fundamental prediction of the standard cosmological model and provides a striking illustration of acoustic oscillations and adiabatic initial conditions in the early universe. © 2013. The American Astronomical Society. All rights reserved. Source


Bennett C.L.,Johns Hopkins University | Larson D.,Johns Hopkins University | Weiland J.L.,Johns Hopkins University | Jarosik N.,Princeton University | And 21 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

We present the final nine-year maps and basic results from the Wilkinson Microwave Anisotropy Probe (WMAP) mission. The full nine-year analysis of the time-ordered data provides updated characterizations and calibrations of the experiment. We also provide new nine-year full sky temperature maps that were processed to reduce the asymmetry of the effective beams. Temperature and polarization sky maps are examined to separate cosmic microwave background (CMB) anisotropy from foreground emission, and both types of signals are analyzed in detail. We provide new point source catalogs as well as new diffuse and point source foreground masks. An updated template-removal process is used for cosmological analysis; new foreground fits are performed, and new foreground-reduced CMB maps are presented. We now implement an optimal C -1 weighting to compute the temperature angular power spectrum. The WMAP mission has resulted in a highly constrained ΛCDM cosmological model with precise and accurate parameters in agreement with a host of other cosmological measurements. When WMAP data are combined with finer scale CMB, baryon acoustic oscillation, and Hubble constant measurements, we find that big bang nucleosynthesis is well supported and there is no compelling evidence for a non-standard number of neutrino species (N eff = 3.84 ± 0.40). The model fit also implies that the age of the universe is t 0 = 13.772 ± 0.059 Gyr, and the fit Hubble constant is H 0 = 69.32 ± 0.80 km s-1 Mpc-1. Inflation is also supported: the fluctuations are adiabatic, with Gaussian random phases; the detection of a deviation of the scalar spectral index from unity, reported earlier by the WMAP team, now has high statistical significance (ns = 0.9608 ± 0.0080); and the universe is close to flat/Euclidean (). Overall, the WMAP mission has resulted in a reduction of the cosmological parameter volume by a factor of 68,000 for the standard six-parameter ΛCDM model, based on CMB data alone. For a model including tensors, the allowed seven-parameter volume has been reduced by a factor 117,000. Other cosmological observations are in accord with the CMB predictions, and the combined data reduces the cosmological parameter volume even further. With no significant anomalies and an adequate goodness of fit, the inflationary flat ΛCDM model and its precise and accurate parameters rooted in WMAP data stands as the standard model of cosmology. © 2013. The American Astronomical Society. All rights reserved.. Source


Larson D.,Johns Hopkins University | Dunkley J.,University of Oxford | Hinshaw G.,NASA | Komatsu E.,University of Texas at Austin | And 17 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

The WMAP mission has produced sky maps from seven years of observations at L2. We present the angular power spectra derived from the seven-year maps and discuss the cosmological conclusions that can be inferred from WMAP data alone. With the seven-year data, the temperature (TT) spectrum measurement has a signal-to-noise ratio per multipole that exceeds unity for l < 919; and in band powers of width Δl = 10, the signal-to-noise ratio exceeds unity up to l = 1060. The third acoustic peak in the TT spectrum is now well measured by WMAP. In the context of a flat ACDM model, this improvement allows us to place tighter constraints on the matter density from WMAP data alone, Ωmh2 = 0.1334+0.0056 -0.0055, and on the epoch of matter-radiation equality, zeq = 3196 +134 -133. The temperature-polarization (TE) spectrum is detected in the seven-year data with a significance of 20σ, compared to 13s with the five-year data. We now detect the second dip in the TE spectrum near l ∼ 450 with high confidence. The TB and EB spectra remain consistent with zero, thus demonstrating low systematic errors and foreground residuals in the data. The low-lEE spectrum, a measure of the optical depth due to reionization, is detected at 5.5σ significance when averaged over l = 2-7: l(l+1)Cl EE/(2π) = 0.074+0.034 -0.025μK2 (68% CL). We now detect the high-l, 24 ≤ l ≤ 800, EE spectrum at over 8σ. The BB spectrum, an important probe of gravitational waves from inflation, remains consistent with zero; when averaged over l = 2-7, l(l + 1)Cl BB/(2π) < 0.055 μK 2 (95% CL). The upper limit on tensor modes from polarization data alone is a factor of two lower with the seven-year data than it was using the five-year data. The data remain consistent with the simple ACDM model: the best-fit TT spectrum has an effective χ2 of 1227 for 1170 degrees of freedom, with a probability to exceed of 9.6%. The allowable volume in the six-dimensional space of ACDM parameters has been reduced by a factor of 1.5 relative to the five-year volume, while the ACDM model that allows for tensor modes and a running scalar spectral index has a factor of three lower volume when fit to the seven-year data. We test the parameter recovery process for bias and find that the scalar spectral index, ns, is biased high, but only by 0.09σ, while the remaining parameters are biased by <0.15σ. The improvement in the third peak measurement leads to tighter lower limits from WMAP on the number of relativistic degrees of freedom (e.g., neutrinos) in the early universe: Neff > 2.7 (95% CL). Also, using WMAP data alone, the primordial helium mass fraction is found to be Y He = 0.28+0.14 -0.15, and with data from higher-resolution cosmic microwave background experiments included, we now establish the existence of pre-stellar helium at >3σ. These new WMAP measurements provide important tests of big bang cosmology. © 2011. The American Astronomical Society. Source

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