1710.05931
Welcome to the multi-messenger era! Lessons from a neutron star merger and the landscape ahead
Metzger
The discovery by Advanced LIGO/Virgo of gravitational waves from the binary NS merger GW170817, and subsequently by astronomers of transient counterparts across the EM spectrum, has initiated the era of multi-messenger astronomy. Given the slew of papers appearing on this event, thought it useful to summarize the EM discoveries in the context of theoretical models and present the views on the major take-away lessons from this watershed event. The weak GRB discovered in close time coincidence with GW170817, and potential evidence for a more powerful off-axis relativistic jet (initially beamed away from our line of sight) from the delayed rise of a non-thermal X-ray and radio orphan afterglow, provides the most compelling evidence yet that cosmological sGRBs originate from binary NS mergers. The luminosity and colors of the early optical emission discovered within a day of the merger agrees strikingly well with original predictions (Metzger+2010) for "kilonova" emission powered by the radioactive decay of r-process nuclei, the NS merger origin of which was initially proposed by Lattimer+Schramm 1974. The transition of the spectral energy distribution to NIR wavelengths on timescales of days matches predictions by Barnes+Kasen 2013 and Tanaka+Hotokezaka 2013 if a portion of the ejecta contains heavy r-process nuclei with higher opacities. The "blue" and "red" ejecta components may possess distinct origins (e.g. dynamical ejecta versus accretion disk outflows), with key implications for the merger physics and the properties of neutron stars. Outline the diversity in the EM emission expected from additional mergers--observed with different binary masses and viewing angles--discovered once LIGO/Virgo reach design sensitivity and NS mergers are discovered as frequently as once per week.
1710.05951
An independent determination of the local Hubble constant
Fernández-Arenas, et al
Obtain H0 from the relationship between the integrated H_beta line luminosity and the velocity dispersion of the ionized gas of HII galaxies and giant HII regions, a standard candle that presently can be used up to z~4. Hubble constant measurements from the combination of the slope of the relation obtained from z<0.2 HII galaxies with the zero point determined from giant HII regions belonging to an 'anchor sample of galaxies for which accurate z-independent distance moduli are available. Data for 36 giant HII regions in 13 galaxies; this data is the first 4 years of obseration of the primary sample of 130 giant HII regions in 73 galaxies with Cepheid determined distances. The best estimate of the Hubble parameter is 71.0±2.8(random)±2.1(systematic) km/s/Mpc. This result is the product of an independent approach and, although at present less precise than the latest SNIa results, it is amenable to substantial improvement.
1710.06168
GW170817 Falsifies dark matter emulators
Boran, et al
Simultaneous detection of GW and EM signals from GW170817 rules out a class of modified gravity theories which dispense with the need for DM. This simultaneous observation also provides the first ever test of Einstein's Weak Equivalence Principle between gravitons and photons. Calculate the Shapiro time delay due to the gravitational potential of the total DM distribution along the LoS to be about 1000 days. Using this estimate from the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma-rays, constrain violations of WEP using the pamaeterized post-Newtonian (PPN) parameter gamma, and is given by gamma_GW - gamma_EM < 3.9e-8.
1710.06427
Constraints from the time lag between gravitational waves and gamma rays: implications of GW170817 and GRB170817A
Shoemaker, Murase
The EM detection of GW170817, including the sGRB within Delta t~2s after the GW arrival, can be used to test various aspects of sources physics and GW propagation. Using GW170817 as the first GW-EM example, show that this event provides a stringent direct test that GWs travel at the speed of light. The gravitational potential of the Milky Way provides a potential sources of Shapiro time delay difference between the arrival of photons and GWs, and demonstrate that the nearly coincident detection of the GW and EM signals can yield strong limits on anomalous gravitational time delay, through updating the previous limits taking in to account details of MW's gravitational potential. Finally, also obtain an intriguing limit on the size of the prompt emission region GRB170817A, and discuss implications for the emission mechanism of sGMBs.
1710.06426
Improved constraints on H0 from a combined analysis of gravitational-wave and electromagnetic emission from GW170817
Guidorzi, et al
H0=74.0±(13.7/5.3) km/s/Mpc, "note that this is in modestly better agreement with the local distance latter than the Planck CMB, though a significant such discrimination will require ~50 such events."
1710.06424
Prospects of the local Hubble parameter measurement using gravitational waves from double neutron stars
Seto, Kyutoku
For a good fraction >~50% of the double NS events within 200 Mpc, could identify their host galaxies. Depending on the DNS merger rate, could measure the local Hubble parameters H_L at the level (Delta H_L/H_L) ~ 0.042 (1 sigma CL), after the 3rd observation run (O3).
1710.06431
Weak lensing magnification of SpARCS galaxy clusters
Turodrica, Hildebrand, et al
Measuring and calibrating relations between cluster observables is critical for resource-limited studies. The mass-richness relation of clusters offers an observationally inexpensive way of estimating masses. Its calibration is essential for cluster and cosmological studies, especially for high-z clusters. WL magnification is a promising and complementary method to shear studies, that can be applied at higher z. Employed the WL magnification method to calibrate the mass-richness relation up to z~1.4. Used SpARCS galaxy cluster candidates (0.2<z<1.4) and optical data from CFHT to test whether magnification can be effetively used to constrain the mass of high-z clusters. LBGs (Lyman-break galaxies) selected using the u-band dropout technique and their colors were used as a BG sample of sources. LBG positions were cross-correlated with the centers of the sample of SpARCS clusters to estimate the magnification signal measured for cluster sub-samples, binned in both z and richness. Detected a WL magnification signal for all bins at a detection significance of 2.6-5.5 sigma. In particular, the significance of the measurement for clusters with z>1.0 is 4.1 sigma; for the entire cluster sample, obtained an average of M_200 of 1.28(+0.23-0.21)e14 Msun. The measurements demonstrated the feasibility of using WL magnification as a viable tool for determining the average halo masses for samples of high-z galaxy clusters. The results also established the success of using galaxy over-densities to select massive clusters at z>1. Additional studies are necessary for further modeling of the various systematic effects discussed.
1710.06739
Gaia data relate 1 cross-match with external catalogues - algorithm and results
Marrese, et al
Combination of high accuracy archive with other archives useful -- the interoperation of archives is based on cross-matching; data retrieval should work not only across data archives but also across wavelength domains. Describe the cross-match algorithm used to pre-computed the match of Gaia DR1 catalogues with a selected list of large optical and IR surveys publicly available. The overall principles of the adopted cross-match algorithm are outlined. Details are given on the developed algorithm, including the methods to account for position errors, proper motions and environment, to define the neighbors and to define the future of merit used to select the most probable counterpart. Statistics on the results are also given. The results of the cross-match are part of the official Gaia DR1 release.
1710.06808
The splash back feature around DES galaxy clusters: galaxy density and weak lensing profiles
Chang, et al
Splashback refers to the process of matter than is accreting onto a DM halo reaching its first orbital apocenter and turning around in its orbit. The cluster-centric radius at which this process occurs, r_sp, defines a halo boundary that is connected to the dynamics of the cluster, in contrast with other common halo boundary definitions such as R_200. A rapid decline in the matter density profile of the halo is expected near r_sp. Measure the galaxy number density and WL mass profiles around RedMapper galaxy clusters in the DES data. For a cluster sample with mean mass 2.5e14 Msun, find strong evidence of a splashback-like steepening of the galaxy density profile and measure r_sp=1.16±0.08 Mpc/h, consistent with earlier SDSS measurements of More+2016 and Baxter+2017. Moreover, the WL measurement demonstrates for the first time the existence of splashback-like steepening of the matter profile of galaxy clusters. Measure r_sp=1.28±0.18 Mpc/h from the WL data, in good agreement with the galaxy density measurements. Applying the analysis to different cluster and galaxy samples, find that consistent with LCDM simulations, r_sp scales with R_200m and does not evolve with redshift over the range 0.3<z<0.6. Also find that potential systematic effects associated wit the RedMapper algorithm may impact the location of r_sp, in particular the choice of scale used to estimate cluster richness. Discuss progress needed to understand the systematic uncertainties and fully exploit forthcoming data from DES and future surveys, emphasizing the importance of more realistic mock catalogs and independent cluster samples.
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