1710.05045
Density split statistics: cosmological constraints from counts and lensing in cells in DES Y1 and SDSS
Gruen, et al
Derive cosmological constraints from the PDF of evolved LS matter density fluctuations. This is done by splitting lines of sight by density based on their count of tracer galaxies, and by measuring both gravitational shear around and counts-in-cells in overdense and underdense lines of sight, in DES Y1 and SDSS data. The analysis uses a perturbation theory model (see companion paper Friedrich+) and is validated using N-body simulation realizations and log-normal mocks. It allows constraints on cosmology, bias and stochasticity of galaxies wrt matter density and, in addition, the skewness of the matter density field. From a Bayesian model comparison, find that the data weakly prefer a connection of galaxies and matter that is stochastic beyond Poisson fluctuations on <= 20 arcmin angular smoothing scale. The two stochasticity models fit yield DES constrains on the matter density Omega_m=0.26+0.04-0.03 and Omega_m=0.28+0.05-0.04 that are consistent with each other. These values also agree with the DES analysis of galaxy and shear 2pt functions (3x2 pt) that only uses second moments of the PDF. Constraints on sigma8 are model dependent (sigma8=0.97+0.07-0.06 and 0.80+0.06-0.07 for the 2 stochasticity models), but consistent with each other and with the 3x2pt results if stochasticity is at the low end of the posterior range. As an additional test of gravity, counts and lensing in cells allow to compare the skewness S3 of the matter density PDF to its LCDM prediction. Find no evidence of excess skewness in any model or data set, with better than 25% relative precision in the skewness estimate from DES alone.
1710.05162
Density spilt statistics: joint model of counts and lensing in cells
Friedrich, Gruen, et al
Present density spit statistics, a framework that studies lensing and counts-in-cells as a function of FG galaxy density, thereby providing a LS measurement of both 2pt and 3pt statistics. The method extends the earlier work on trough lensing and is summarized as follows: given a FG (low z) population of galaxies, divide the sky into subareas of equal size but distinct galaxy density. Then measure lensing around uniformly spaced points separately in each of these subareas, as well as counts-in-cells statistics (CiC). The lensing signals trace the matter density contrast around regions of fixed galaxy density. Through the CiC measurements this can be related to the density profile around regions of fixed matter density. Together, these measurements constitute a powerful probe of cosmology, the skewness of the density field and the connection of galaxies and matter. In this paper, show how to model both the density split lensing signal and CiC from basic ingredients: a non-linear power spectrum, clustering hierarchy coefficients from perturbation theory and a parametric model for galaxy bias and shot-noise. Using N-body simulations, demonstrate that this model is sufficiently accurate for a cosmological analysis on year 1 data from the DES.
1710.05434
Electromagnetic evidence that SSS17a is the result of a binary neutron star merger
Kilpatrick, et al
11 hrs after the detection of GW source GW170817 by the LIGO and Virgo interferometers, an associated optical transient SSS17a was discovered in the galaxy NGC 4993. While the gravitational wave data indicate GW170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints of the nature of that system. Here, synthesize all optical and NIR photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration. Find that SSS17a is unlike other known transients. The source is best described by theoretical models of a kilo nova consisting of radioactive elements produced by rapid neutron capture (the r-process). Find that SSS17a was the result of a binary neutron star merger, reinforcing the gravitational wave result.
1710.05833
Multi-messenger observations of a binary neutron star merger
LIGO, Virgo, Fermi GBM, INTEGRAL, IceCube, AstroSat, IPN, Insight-Hxmt, ANTARES, Swift, AGILE, 1M2H, DEC GW-EM, DES, DLT40, GRAWITA, Fermi-LAT, ATCA, +50 others
On 2017 August 17 a binary NS coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40±8 Mpc and with component masses consistent with NS. The component masses were later measured to be in the range 0.86 to 2.26 Msun. An extensive observing campaign was launched across the EM spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mac) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1m Swope telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early UV observations revealed a blue transient that faded within 48 hrs. Optical and infrared observations showed a reward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-IR emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches.
1710.05835
A gravitational-wave standard siren measurement of the Hubble constant
Abbott, + >1300 other authors
Combine the distance to the source inferred purely from the GW signal with the recession velocity inferred from redshifts using EM data. ...determine the Hubble constant to be 70.0+12.0-8.0 km/s/Mpc (68% CL). Consistent with existing measurements, while being completely independent of them.
1710.05457
The Electromagnetic counterpart of the binary neutron star merger LIGO/VIRGO GW170817. VI. Radio constraints on a relativistic jet and predictions for late-time emission from the kilonova ejecta
Alexander, et al
...EM counterpart detected in optical 13.7 hrs after merger, and millimeter 2.41 days post merger. 6GHz detection at 19.5 and 39.2 days after the merger, but not in an earlier observation at 2.5 days. No detection of dm/mm emission at the position of the optical counterpart at frequencies of 10-97.5 Ghz at times ranging from 0.6 to 30 days post merger, ruling out an on-axis sGRB for energies >=1e48 erg. For fiducial sGRB parameters, the limits require an observer viewer angle of >~20 deg. The radio and X-ray data can be jointly explained as the afterglow emission from an sGRB with a jet energy of 1e49-50 erg that exploded in a uniform density environment with n~1e-4 to 1e-2 cm^-3, viewed at an angle of ~20-40 degrees from the jet axis. Using the results of the light curve and spectral modeling, in conjunction with the inference of the circumbinary density, predict the emergence of late-time radio emission from the deceleration of the kilonova ejecta on a timescale of ~5-10 years that will remain detectable for decades with next-generation radio facilities, makingGW170817 a compelling target for long-term radio monitoring.
1710.05438
The electromagnetic counterpart of the binary neutron star merger LIGO/VIRGO GW170817. VIII. a comparison to cosmological short-duration gamma-ray bursts
Fong, et al
Compare with a sample of 36 sGRBs spanning 0.12<z<2.6 discovered over 2004-2017. Find that the counterpart to GW170817 has an isotropic-equivalent luminosity that is ~3000x less than the median value of on-axis short GRB X-ray afterglows, and >1e4 times less than that for detected sGRB radio afterglows. The allowed jet energies and particle densities inferred from the radio and X-ray counterparts to GW170817 and on-axis sGRB afterglows are remarkably similar, suggesting that viewing angle effects are the dominant, and perhaps only, difference in their observed radio and X-ray behavior. From comparison to previous claimed kilonovae following sGRBs, find that the optical and near-IR counterpart to GW170817 is comparatively under-luminous by a factor of 3-5, indicating a range of kilonova luminosities and timescales. A comparison of the optical limits following sGRBs on <1day timescales also rules out a "blue" kilo nova of comparable optical isotropic-equivalent luminosity in one previous sGRB. Investigate the host galaxy NGC4993, in the context of sGRB host galaxy stellar population properties. Find that NGC4993 is superlative in terms of its large luminosity, old stellar population age, and low SFR compared to previous sGRB hosts. Additional events within Advanced LIGO/VIGO volume will be crucial in delineating the properties of the host galaxies of NS-NS mergers, and connecting them to their cosmological counterparts.
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