scholarly journals Detectability of neutron star merger afterglows

2019 ◽  
Vol 488 (2) ◽  
pp. 2405-2411 ◽  
Author(s):  
Ore Gottlieb ◽  
Ehud Nakar ◽  
Tsvi Piran
Keyword(s):  
Neutron Star ◽  
Numerical Simulations ◽  
Peak Time ◽  
Low Density ◽  
Viewing Angle ◽  
Estimated Parameters ◽  
Analytic Expressions

ABSTRACT VLBI and JVLA observations revealed that GW170817 involved a narrow jet (θj ≈ 4°) that dominated the afterglow peak at our viewing angle, θobs ≈ 20°. This implies that at the time of the afterglow peak, the observed signal behaved like an afterglow of a top-hat jet seen at θobs ≫ θj, and it can be modelled by analytic expressions that describe such jets. We use a set of numerical simulations to calibrate these analytic relations and obtain generic equations for the peak time and flux of such an afterglow as seen from various observing angles. Using the calibrated equations and the estimated parameters of GW170817, we estimate the detectability of afterglows from future double neutron star mergers during the Advanced LIGO/Virgo observation run O3. GW170817 took place at a relatively low-density environment. Afterglows of similar events will be detectable only at small viewing angles, θobs ≲ 20°, and only 20 per cent of the GW detections of these events will be accompanied by a detectable afterglow. At higher densities, more typical to sGRB sites, up to $70\,\rm{per\,cent}$ of the GW detections are expected to be followed by a detectable afterglow, typically at θobs ∼ 30°. We also provide the latest time one should expect an afterglow detection. We find that for typical parameters, if the jet emission had not been detected within about a year after the merger, it is unlikely to be ever detected.

scholarly journals Jet Propagation in Neutron Star Mergers and GW170817

2019 ◽  
Author(s):  
Hamid Hamidani ◽  
Kenta Kiuchi ◽  
Kunihito Ioka
Keyword(s):  
Neutron Star ◽  
Numerical Simulations ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Expansion Velocity ◽  
Analytic Model ◽  
Binary Neutron Star ◽  
Central Engine ◽  
Relativistic Jet ◽  
Wave Event

Abstract The gravitational wave event from the binary neutron star (BNS) merger GW170817 and the following multi-messenger observations present strong evidence for i) merger ejecta expanding with substantial velocities and ii) a relativistic jet which had to propagate through the merger ejecta. The ejecta’s expansion velocity is not negligible for the jet head motion, which is a fundamental difference from the other systems like collapsars and active galactic nuclei. Here we present an analytic model of the jet propagation in an expanding medium. In particular, we notice a new term in the expression of the breakout time and velocity. In parallel, we perform a series of over a hundred 2D numerical simulations of jet propagation. The BNS merger ejecta is prepared based on numerical relativity simulations of a BNS merger with the highest-resolution to date. We show that our analytic results agree with numerical simulations over a wide parameter space. Then we apply our analytic model to GW170817, and obtain two solid constraints on: i) the central engine luminosity as Liso, 0 ∼ 3 × 1049 − 2.5 × 1052 erg s−1, and on ii) the delay time between the merger and engine activation t0 − tm < 1.3 s. The engine power implies that the apparently-faint short gamma-ray burst (sGRB) sGRB 170817A is similar to typical sGRBs if observed on-axis.

scholarly journals Quantitative assessment of the identifiability of pipeline systems★The research was carried out within the project III.17.4.3 of the Fundamental research program of SB RAS (AAAA-A17-117030310437-4)

2018 ◽  
Vol 39 ◽  
pp. 03004 ◽  
Author(s):  
Nikolay N. Novitsky ◽  
Oksana A. Grebneva
Keyword(s):  
Quantitative Assessment ◽  
Identifiability Analysis ◽  
Estimated Parameters ◽  
New Concepts ◽  
Pipeline Systems ◽  
Analytic Expressions ◽  
Fundamental Research ◽  
Optimal Measurements ◽  
Water Gas ◽  
Parametric Identifiability

The article is devoted to the issues of quantitative assessment of the identifiability of the pipeline systems (heat, water, gas supply systems etc.). Identifiability is first considered as a complex property, including such particular properties as observability and parametric identifiability. A brief description of the topic relevance and a review of available development in this sphere allow giving the structuring of identifiability analysis problems. The technique of differentiate quantitative analysis of this property is disclosed. It based on the use of analytical expressions for covariance matrices of parameters. New concepts of experimental matrices, parametric identifiability and observability of pipeline systems are introduced. Analytic expressions for these matrices are given. The substantiation of the integral indicators of the pipeline systems identifiability is presented, including the covariance matrix determinant for the estimated parameters and the relative variance of the prediction for non-measurable state parameters. The analytical interrelation of these indicators is opened. These indicators can be accepted in a role of criteria at decision of synthesis problems for optimal measurements composition.

Experimental parameter identification of flexible joint robot manipulators

Robotica ◽  
2017 ◽  
Vol 36 (3) ◽  
pp. 313-332 ◽  
Author(s):  
Roger Miranda-Colorado ◽  
Javier Moreno-Valenzuela
Keyword(s):  
Parameter Identification ◽  
Numerical Simulations ◽  
Least Squares ◽  
Robot Manipulators ◽  
Experimental Parameter ◽  
Velocity Estimation ◽  
Identification Procedure ◽  
Flexible Joint ◽  
Identification Method ◽  
Estimated Parameters

SUMMARYThis paper contributes by presenting a parameter identification procedure for n-degrees-of-freedom flexible joint robot manipulators. An advantage of the given procedure is the obtaining of robot parameters in a single experiment. Guidelines are provided for the computing of the joint position filtering and velocity estimation. The method relies in the filtered robot model, for which no acceleration measurements are required. The filtered model is expressed in regressor form, which allows applying a parameter identification procedure based on the least squares algorithm. In order to assess the performance of the proposed parameter identification scheme, an implementation of a least squares with forgetting factor (LSFF) parameter identification method is carried out. In order to assess the reliability of the tested identification schemes, a model-based trajectory tracking controller has been implemented twice in different conditions: one control experiment using the estimated parameters provided by the proposed scheme, and another experiment using the parameters given by the LSFF method. These real-time control experiments are compared with respect to numerical simulations using the estimated parameters for each identification method. For the proposed scheme, the comparison between experiments and numerical simulations indicates better accuracy in the torque and position prediction.

scholarly journals Numerical simulations of neutron star-black hole binaries in the near-equal-mass regime

2019 ◽  
Vol 99 (10) ◽  
Author(s):  
F. Foucart ◽  
M. D. Duez ◽  
L. E. Kidder ◽  
S. M. Nissanke ◽  
H. P. Pfeiffer ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Numerical Simulations ◽  
Equal Mass ◽  
Black Hole Binaries

scholarly journals Nuclear “pasta” structures in low-density nuclear matter and properties of the neutron-star crust

2013 ◽  
Vol 88 (2) ◽  
Author(s):  
Minoru Okamoto ◽  
Toshiki Maruyama ◽  
Kazuhiro Yabana ◽  
Toshitaka Tatsumi
Keyword(s):  
Neutron Star ◽  
Nuclear Matter ◽  
Low Density ◽  
Neutron Star Crust

Modeling the ISM: Molecular Gas, Ionizing Radiation, and Numerical Simulations

1999 ◽  
Vol 190 ◽  
pp. 84-92
Author(s):  
Joel N. Bregman
Keyword(s):  
Ionizing Radiation ◽  
Numerical Simulations ◽  
Molecular Cloud ◽  
Conversion Factor ◽  
Magellanic Clouds ◽  
Molecular Gas ◽  
Disk Galaxies ◽  
Low Density ◽  
B Stars ◽  
Magellanic Stream

Three different topics regarding the ISM in the Magellanic Clouds are discussed. First, we examine how the Magellanic Stream can be used as a tracer of the ionizing radiation leaking out of Galaxy and the Magellanic Clouds. We show that the radiation reaching the Magellanic Stream is less than 1% of the ionizing radiation produced by Galactic 0 and B stars. Since about 14% of the ionizing radiation from these stars is required to ionize the Reynolds layer, which is within 1 kpc of the disk, most of this radiation must be absorbed before reaching the Stream.Second, we examine the reliability of using CO as a tracer of H2 in regions of low or modest column densities (not giant molecular cloud complexes). For our Galaxy, the usual CO to H2 conversion factor overlooks a considerable amount of H2 and the evidence suggests that this may be true in the LMC as well. Finally, we present numerical hydrodynamical calculations of the interstellar medium in disk galaxies for a region of size 2 kpc along the plane and 15 kpc out of the plane. The simulations reveal a rich structure of low density hot regions separated by cold dense material, with the resulting position velocity diagrams being qualitatively similar to the recent HI studies of the LMC. A number of other aspects of these simulations are discussed also.

NEUTRON STAR MASS CORRELATION WITH SOUND VELOCITY AND INCOMPRESSIBILITY AT THE STAR CENTER IN THE POLYTROPIC APPROXIMATION

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1575-1582
Author(s):  
L. FERRARI ◽  
P. C. R. ROSSI ◽  
M. MALHEIRO
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Nuclear Matter ◽  
Sound Velocity ◽  
Mean Field ◽  
Star Mass ◽  
Mean Field Models ◽  
Neutron Star Mass ◽  
Analytic Expressions ◽  
Walecka Model

In this paper we use a polytropic approximation to the equation of state for the interior of neutrons stars, described by relativistic hadronic mean field models. In this approximation, it is possible to obtain analytic expressions for the sound velocity and the incompressibility at the star center. We found a correlation between these quantities and the star mass. Using two well-known parametrizations of the nonlinear Walecka model for nuclear matter composed only of protons, neutrons and electron in β equilibrium, we obtain for a star mass of 1.43 M⊙ a central incompressibility Kc = (3000±100), around ten times the nuclear matter incompressibility, and a central sound velocity (v/c)2 ~ 0.3.

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