Search results for "RAV"
showing 10 items of 5866 documents
Absolute kinematics of radio-source components in the complete S5 polar cap sample: IV. Proper motions of the radio cores over a decade and spectral …
2016
We have carried out a high-precision astrometric analysis of two very-long-baseline-interferometry (VLBI) epochs of observation of the 13 extragalactic radio sources in the complete S5 polar cap sample. The VLBI epochs span a time baseline of ten years and enable us to achieve precisions in the proper motions of the source cores up to a few micro-arcseconds per year. The observations were performed at 14.4 GHz and 43.1 GHz, and enable us to estimate the frequency core-shifts in a subset of sources, for which the spectral-index distributions can be computed. We study the source-position stability by analysing the changes in the relative positions of fiducial source points (the jet cores) ove…
Relativistic simulations of black hole-neutron star coalescence: the jet emerges
2014
We perform magnetohydrodynamic simulations in full general relativity (GRMHD) of a binary black hole-neutron star on a quasicircular orbit that undergoes merger. The binary mass ratio is 3:1, the black hole initial spin parameter $a/m=0.75$ ($m$ is the black hole Christodoulou mass) aligned with the orbital angular momentum, and the neutron star is an irrotational $\Gamma=2$ polytrope. About two orbits prior to merger (at time $t=t_B$), we seed the neutron star with a dynamically weak interior dipole magnetic field that extends into the stellar exterior. At $t=t_B$ the exterior has a low-density atmosphere with constant plasma parameter $\beta\equiv P_{\rm gas}/P_{\rm mag}$. Varying $\beta$…
Binary neutron star mergers: a jet engine for short gamma-ray bursts
2016
We perform magnetohydrodynamic simulations in full general relativity (GRMHD) of quasi-circular, equal-mass, binary neutron stars that undergo merger. The initial stars are irrotational, $n=1$ polytropes and are magnetized. We explore two types of magnetic-field geometries: one where each star is endowed with a dipole magnetic field extending from the interior into the exterior, as in a pulsar, and the other where the dipole field is initially confined to the interior. In both cases the adopted magnetic fields are initially dynamically unimportant. The merger outcome is a hypermassive neutron star that undergoes delayed collapse to a black hole (spin parameter $a/M_{\rm BH} \sim 0.74$) imme…
The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole
2021
Full list of authors: Narayan, Ramesh; Palumbo, Daniel C. M.; Johnson, Michael D.; Gelles, Zachary; Himwich, Elizabeth; Chang, Dominic O.; Ricarte, Angelo; Dexter, Jason; Gammie, Charles F.; Chael, Andrew A.; Event Horizon Telescope Collaboration; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Algaba, Juan Carlos; Anantua, Richard; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David Baloković, Mislav; Barrett, John; Benson, Bradford A.; Bintley, Dan; Blackburn, Lindy; Blundell, Raymond; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Boyce, Hope; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broderick, Avery E.; Broguiere, Domini…
Induced scalarization in boson stars and scalar gravitational radiation
2012
The dynamical evolution of boson stars in scalar-tensor theories of gravity is considered in the physical (Jordan) frame. We focus on the study of spontaneous and induced scalarization, for which we take as initial data configurations on the well-known S-branch of a single boson star in general relativity. We show that during the scalarization process a strong emission of scalar radiation occurs. The new stable configurations (S-branch) of a single boson star within a particular scalar-tensor theory are also presented.
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 9 Spectroscopic …
2012
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2012 RAS © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 10 and 11 galaxy…
2014
We present a one per cent measurement of the cosmic distance scale from the detections of the baryon acoustic oscillations in the clustering of galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey III (SDSS-III). Our results come from the Data Release 11 (DR11) sample, containing nearly one million galaxies and covering approximately $8\,500$ square degrees and the redshift range $0.2<z<0.7$. We also compare these results with those from the publicly released DR9 and DR10 samples. Assuming a concordance $\Lambda$CDM cosmological model, the DR11 sample covers a volume of 13\,Gpc${}^3$ and is the largest region of the Universe ever su…
GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs
2019
We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1$\mathrm{M}_\odot$ during the first and second observing runs of the Advanced gravitational-wave detector network. During the first observing run (O1), from September $12^\mathrm{th}$, 2015 to January $19^\mathrm{th}$, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November $30^\mathrm{th}$, 2016 to August $25^\mathrm{th}$, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary …
A first search for coincident gravitational waves and high energy neutrinos using LIGO, Virgo and ANTARES data from 2007
2013
A search for high-energy neutrinos coming from the direction of the Sun has been performed using the data recorded by the ANTARES neutrino telescope during 2007 and 2008. The neutrino selection criteria have been chosen to maximize the selection of possible signals produced by the self-annihilation of weakly interacting massive particles accumulated in the centre of the Sun with respect to the atmospheric background. After data unblinding, the number of neutrinos observed towards the Sun was found to be compatible with background expectations. The 90% CL upper limits in terms of spin-dependent and spin-independent WIMP-proton cross-sections are derived and compared to predictions of two sup…
Are fast radio bursts the most likely electromagnetic counterpart of neutron star mergers resulting in prompt collapse?
2018
Inspiraling and merging binary neutron stars (BNSs) are important sources of both gravitational waves and coincident electromagnetic counterparts. If the BNS total mass is larger than a threshold value, a black hole ensues promptly after merger. Through a statistical study in conjunction with recent LIGO/Virgo constraints on the nuclear equation of state, we estimate that up to $\sim 25\%$ of BNS mergers may result in prompt collapse. Moreover, we find that most models of the BNS mass function we study here predict that the majority of prompt-collapse BNS mergers have $q\gtrsim 0.8$. Prompt-collapse BNS mergers with mass ratio $q \gtrsim 0.8$ may not be accompanied by detectable kilonovae o…