Search results for "Aga"
showing 10 items of 4366 documents
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…
Search for eccentric binary black hole mergers with advanced LIGO and advanced Virgo during their first and second observing runs
2019
When formed through dynamical interactions, stellar-mass binary black holes may retain eccentric orbits ($e>0.1$ at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically-formed binaries from isolated binary black hole mergers. Current template-based gravitational-wave searches do not use waveform models associated to eccentric orbits, rendering the search less efficient to eccentric binary systems. Here we present results of a search for binary black hole mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. The search uses min…
A Standard Siren Measurement of the Hubble Constant from GW170817 without the Electromagnetic Counterpart
2019
We perform a statistical standard siren analysis of GW170817. Our analysis does not utilize knowledge of NGC 4993 as the unique host galaxy of the optical counterpart to GW170817. Instead, we consider each galaxy within the GW170817 localization region as a potential host; combining the redshift from each galaxy with the distance estimate from GW170817 provides an estimate of the Hubble constant, $H_0$. We then combine the $H_0$ values from all the galaxies to provide a final measurement of $H_0$. We explore the dependence of our results on the thresholds by which galaxies are included in our sample, as well as the impact of weighting the galaxies by stellar mass and star-formation rate. Co…
Properties of the Binary Neutron Star Merger GW170817
2019
On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal, GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we improve initial estimates of the binary's properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also compare results inferred using several signal models, which ar…
Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
2017
On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anticoincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is $5.0\times 10^{-8}$. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short gamma-ray bursts. We use the ob…
X-ray emission from stellar jets by collision against high-density molecular clouds: an application to HH 248
2015
We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts against a dense molecular cloud. This scenario may be usual for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud by 2D axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig-Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10 MK, consistent with producti…
MOJAVE. XIII. PARSEC-SCALE AGN JET KINEMATICS ANALYSIS BASED ON 19 YEARS OF VLBA OBSERVATIONS AT 15 GHz
2016
We present 1625 new 15 GHz (2 cm) VLBA images of 295 jets associated with active galactic nuclei (AGNs) from the MOJAVE and 2 cm VLBA surveys, spanning observations between 1994 Aug 31 and 2013 Aug 20. For 274 AGNs with at least 5 VLBA epochs, we have analyzed the kinematics of 961 individual bright features in their parsec-scale jets. A total of 122 of these jets have not been previously analyzed by the MOJAVE program. In the case of 451 jet features that had at least 10 epochs, we also examined their kinematics for possible accelerations. At least half of the well-sampled features have non-radial and/or accelerating trajectories, indicating that non-ballistic motion is common in AGN jets.…
Search for heavy neutral lepton production in K+ decays to positrons
2020
A search for heavy neutral lepton ($N$) production in $K^+\to e^+N$ decays using the data sample collected by the NA62 experiment at CERN in 2017--2018 is reported. Upper limits of the extended neutrino mixing matrix element $|U_{e4}|^2$ are established at the level of $10^{-9}$ over most of the accessible heavy neutral lepton mass range 144--462 MeV/$c^2$, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The $|U_{e4}|^2$ range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/$c^2$.
Determining the dark matter mass with DeepCore
2013
Cosmological and astrophysical observations provide increasing evidence of the existence of dark matter in our Universe. Dark matter particles with a mass above a few GeV can be captured by the Sun, accumulate in the core, annihilate, and produce high energy neutrinos either directly or by subsequent decays of Standard Model particles. We investigate the prospects for indirect dark matter detection in the IceCube/DeepCore neutrino telescope and its capabilities to determine the dark matter mass.
Testing standard and nonstandard neutrino physics with cosmological data
2012
Cosmological constraints on the sum of neutrino masses and on the effective number of neutrino species in standard and nonstandard scenarios are computed using the most recent available cosmological data. Our cosmological data sets include the measurement of the baryonic acoustic oscillation (BAO) feature in the data release 9 CMASS sample of the baryon oscillation spectroscopic survey. We study in detail the different degeneracies among the parameters, as well as the impact of the different data sets used in the analyses. When considering bounds on the sum of the three active neutrino masses, the information in the BAO signal from galaxy clustering measurements is approximately equally pow…