scholarly journals Beaming as an explanation of the repetition/width relation in FRBs

2020 ◽  
Vol 497 (3) ◽  
pp. 3076-3082 ◽  
Author(s):  
L Connor ◽  
M C Miller ◽  
D W Gardenier
Keyword(s):  
Continuous Distribution ◽  
Selection Effect ◽  
Relativistic Effects ◽  
Lorentz Factor ◽  
Energy Scale ◽  
Opening Angle ◽  
Striking Difference ◽  
Simple Explanation ◽  
Intensity Mapping ◽  
Event Rates

ABSTRACT It is currently not known if repeating fast radio bursts (FRBs) are fundamentally different from those that have not been seen to repeat. One striking difference between repeaters and apparent non-repeaters in the Canadian Hydrogen Intensity Mapping Experiment sample is that the once-off events are typically shorter in duration than sources that have been detected two or more times. We offer a simple explanation for this discrepancy based on a selection effect due to beamed emission, in which highly beamed FRBs are less easily observed to repeat, but are abundant enough to detect often as once-off events. The explanation predicts that there is a continuous distribution of burst duration – not a static bimodal one – with a correlation between repetition rate and width. Pulse width and opening angle may be related by relativistic effects in shocks, where short-duration bursts have small solid angles due to a large common Lorentz factor. Alternatively, the relationship could be a geometric effect where narrow beams sweep past the observer more quickly, as with pulsars. Our model has implications for the FRB emission mechanism and energy scale, volumetric event rates, and the application of FRBs to cosmology.

scholarly journals Low-frequency, one-armed oscillations in black hole accretion flows obtained from direct 3D MHD simulations

2006 ◽  
Vol 2 (S238) ◽  
pp. 405-406
Author(s):  
Mami Machida ◽  
Ryoji Matsumoto
Keyword(s):  
Black Hole ◽  
Low Frequency ◽  
Maximum Velocity ◽  
Relativistic Effects ◽  
Newtonian Potential ◽  
Opening Angle ◽  
Accretion Flows ◽  
Black Hole Accretion ◽  
Mhd Simulations ◽  
Hole Accretion

AbstractWe present the results of global 3D MHD simulations of optically thin black hole accretion flows. The initial disk is embedded in a low density, spherical, isothermal halo and threaded by weak (β ≡ Pgas/Pmag = 100) toroidal magnetic field. General relativistic effects are simulated by using the pseudo-Newtonian potential. When the Maxwell stress in the innermost region of the disk is reduced due to the loss of magnetic flux or by decrease of disk temperature, inner torus is created around 4 – 10rs. We found that in such an inner torus, one-armed (m = 1) density enhancement grows and that the inner torus oscillates quasi-periodically. The oscillation period is about 0.1s when we assume a 10M⊙ black hole. This frequency agrees with the low-frequency QPOs observed in low/hard state of black hole candidates. The disk ejects winds whose opening angle is about 30 degree. The maximum velocity of the wind is about 0.05c.

scholarly journals Accelerating AGN jets to parsec scales using general relativistic MHD simulations

2019 ◽  
Vol 490 (2) ◽  
pp. 2200-2218 ◽  
Author(s):  
K Chatterjee ◽  
M Liska ◽  
A Tchekhovskoy ◽  
S B Markoff
Keyword(s):  
Ambient Medium ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Long Baseline ◽  
General Relativistic ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations ◽  
Jet Collimation ◽  
Sheath Structure

ABSTRACT Accreting black holes produce collimated outflows, or jets, that traverse many orders of magnitude in distance, accelerate to relativistic velocities, and collimate into tight opening angles. Of these, perhaps the least understood is jet collimation due to the interaction with the ambient medium. In order to investigate this interaction, we carried out axisymmetric general relativistic magnetohydrodynamic simulations of jets produced by a large accretion disc, spanning over 5 orders of magnitude in time and distance, at an unprecedented resolution. Supported by such a disc, the jet attains a parabolic shape, similar to the M87 galaxy jet, and the product of the Lorentz factor and the jet half-opening angle, γθ ≪ 1, similar to values found from very long baseline interferometry (VLBI) observations of active galactic nuclei (AGNs) jets; this suggests extended discs in AGNs. We find that the interaction between the jet and the ambient medium leads to the development of pinch instabilities, which produce significant radial and lateral variability across the jet by converting magnetic and kinetic energy into heat. Thus pinched regions in the jet can be detectable as radiating hotspots and may provide an ideal site for particle acceleration. Pinching also causes gas from the ambient medium to become squeezed between magnetic field lines in the jet, leading to enhanced mass loading and deceleration of the jet to non-relativistic speeds, potentially contributing to the spine-sheath structure observed in AGN outflows.

scholarly journals On the cosmological evolution of long gamma-ray burst properties

2019 ◽  
Vol 488 (4) ◽  
pp. 5823-5832 ◽  
Author(s):  
Nicole M Lloyd-Ronning ◽  
Aycin Aykutalp ◽  
Jarrett L Johnson
Keyword(s):  
Star Formation ◽  
Gamma Ray ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Selection Effect ◽  
Cosmological Evolution ◽  
Opening Angle ◽  
Redshift Distribution ◽  
Isotropic Energy ◽  
Gamma Ray Burst

ABSTRACT We examine the relationship between a number of long gamma-ray burst (lGRB) properties (isotropic emitted energy, luminosity, intrinsic duration, jet opening angle) and redshift. We find that even when accounting for conservative detector flux limits, there appears to be a significant correlation between isotropic equivalent energy and redshift, suggesting cosmological evolution of the lGRB progenitor. Analysing a sub-sample of lGRBs with jet opening angle estimates, we find the beaming-corrected lGRB emitted energy does not correlate with redshift, but jet opening angle does. Additionally, we find a statistically significant anticorrelation between the intrinsic prompt duration and redshift, even when accounting for potential selection effects. We also find that, for a given redshift, isotropic energy is positively correlated with intrinsic prompt duration. None of these GRB properties appear to be correlated with galactic offset. From our selection-effect-corrected redshift distribution, we estimate a co-moving rate density for lGRBs, and compare this to the global cosmic star formation rate (SFR). We find the lGRB rate mildly exceeds the global star formation rate between a redshift of 3 and 5, and declines rapidly at redshifts above this (although we cannot constrain the lGRB rate above a redshift of about 6 due to sample incompleteness). We find the lGRB rate diverges significantly from the SFR at lower redshifts. We discuss both the correlations and lGRB rate density in terms of various lGRB progenitor models and their apparent preference for low-metallicity environments.

scholarly journals BL LAC POPULATION STUDY AT HIGH ENERGIES

2014 ◽  
Vol 28 ◽  
pp. 1460177
Author(s):  
LUCIE GÉRARD ◽  
GILLES HENRI ◽  
SANTIAGO PITA ◽  
MICHAEL PUNCH
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Parent Population ◽  
High Energies ◽  
Relativistic Jet ◽  
Radiative Model ◽  
Doppler Factor ◽  
Bl Lacs

In the framework of Active Galactic Nuclei (AGN) unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the relativistic jet compared to the line of sight. BL Lacs would be the objects whose jet is oriented towards us, their emission being amplified by the relativistic Doppler boosting. Constraints arising from fast variability and/or large optical depth to pair production commonly imply large Lorentz factors. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this unification scheme. Indeed, the high values of Doppler factor needed in the simplest radiative model to explain the emission of these sources imply a large density for the parent population. A possible solution to this Doppler factor crisis lies in considering different geometries for the jet. In this study, we use the BL Lacs detected at HE and VHE to investigate the intrinsic properties of the associated parent population. Using the results presented in Fermi's second AGN catalog and performing MC simulations of the parent population, we constrain the jet parameters: its intrinsic luminosity, Lorentz factor and geometric opening angle. The simulated density of parent population and Doppler factors of the objects detectable at HE within this population are presented according to the jet parameters.

scholarly journals Afterglow light curves from misaligned structured jets

2020 ◽  
Vol 493 (3) ◽  
pp. 3521-3534 ◽  
Author(s):  
Paz Beniamini ◽  
Jonathan Granot ◽  
Ramandeep Gill
Keyword(s):  
Light Curve ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Light Curves ◽  
Opening Angle ◽  
Model Parameters ◽  
Narrow Strip ◽  
Double Peaks ◽  
Wide Range ◽  
Jet Structure

ABSTRACT GRB 170817A/GW 170817 is the first gamma-ray burst (GRB) clearly viewed far from the GRB jet’s symmetry axis. Its afterglow was densely monitored over a wide range of frequencies and times. It has been modelled extensively, primarily numerically, and although this endeavour was very fruitful, many of the underlying model parameters remain undetermined. We provide analytic modelling of GRB afterglows observed off-axis, considering jets with a narrow core (of half-opening angle θc) and power-law wings in energy per unit solid angle (ϵ = ϵcΘ−a where Θ = [1 + (θ/θc)2]1/2) and initial specific kinetic energy (Γ0 − 1 = [Γc, 0 − 1]Θ−b), as well as briefly discuss Gaussian jets. Our study reveals qualitatively different types of light curves that can be viewed in future off-axis GRBs, with either single or double peaks, depending on the jet structure and the viewing angle. Considering the light-curve shape rather than the absolute normalizations of times and/or fluxes, removes the dependence of the light curve on many of the highly degenerate burst parameters. This study can be easily used to determine the underlying jet structure, significantly reduce the effective parameter space for numerical fitting attempts and provide physical insights. As an illustration, we show that for GRB 170817A, there is a strong correlation between the allowed values of Γc, 0 and b, leading to a narrow strip of allowed solutions in the Γc, 0–b plane above some minimal values Γc, 0 ≳ 40, b ≳ 1.2. Furthermore, the Lorentz factor of the material dominating the early light curve can be constrained by three independent techniques to be Γ0(θmin, 0) ≈ 5–7.

scholarly journals The evolution of gamma-ray burst jet opening angle through cosmic time

2020 ◽  
Vol 494 (3) ◽  
pp. 4371-4381 ◽  
Author(s):  
Nicole Lloyd-Ronning ◽  
Valeria U Hurtado ◽  
Aycin Aykutalp ◽  
Jarrett Johnson ◽  
Chiara Ceccobello
Keyword(s):  
Massive Star ◽  
Gamma Ray ◽  
High Redshift ◽  
Cosmic Time ◽  
Selection Effect ◽  
Mass Function ◽  
Average Density ◽  
Initial Mass Function ◽  
Opening Angle ◽  
Stellar Envelope

ABSTRACT Jet opening angles of long gamma-ray bursts (lGRBs) appear to evolve in cosmic time, with lGRBs at higher redshifts being on average more narrowly beamed than those at lower redshifts. We examine the nature of this anticorrelation in the context of collimation by the progenitor stellar envelope. First, we show that the data indicate a strong correlation between gamma-ray luminosity and jet opening angle, and suggest this is a natural selection effect – only the most luminous GRBs are able to successfully launch jets with large opening angles. Then, by considering progenitor properties expected to evolve through cosmic time, we show that denser stars lead to more collimated jets; we argue that the apparent anticorrelation between opening angle and redshift can be accounted for if lGRB massive star progenitors at high redshifts have higher average density compared to those at lower redshifts. This may be viable for an evolving initial mass function (IMF) – under the assumption that average density scales directly with mass, this relationship is consistent with the form of the IMF mass evolution suggested in the literature. The jet angle–redshift anticorrelation may also be explained if the lGRB progenitor population is dominated by massive stars at high redshift, while lower redshift lGRBs allow for a greater diversity of progenitor systems (that may fail to collimate the jet as acutely). Overall, however, we find both the jet angle–redshift anticorrelation and jet angle–luminosity correlation are consistent with the conditions of jet launch through, and collimation by, the envelope of a massive star progenitor.

scholarly journals BL LAC POPULATION STUDY: EARLY RESULTS USING THE Fermi 11-MONTH CATALOG

2012 ◽  
Vol 08 ◽  
pp. 327-330
Author(s):  
LUCIE GÉRARD ◽  
SANTIAGO PITA ◽  
MICHAEL PUNCH ◽  
GILLES HENRI
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Lorentz Factor ◽  
Line Of Sight ◽  
Opening Angle ◽  
Parent Population ◽  
Early Results ◽  
Bl Lac ◽  
Source Sample ◽  
Bl Lacs

In the framework of AGN unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the jet compared to our line of sight. BL Lacs would be those objects whose jet is oriented towards us, Doppler boosting the emission. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this scheme, since the high values of Doppler factors needed to explain the emission of these sources imply a large density for the parent population. We studied the BL Lac source sample detected by Fermi after 11 months of observation. Using the data presented in Fermi's first AGN catalog, we put constraints on the intrinsic characteristics of this BL Lac population, such as the intrinsic luminosity and Lorentz factor distributions. Based on these results, we used Monte Carlo simulations to constrain the space density of the parent population and the jet opening angle.

scholarly journals Multi-wavelength spectroscopic probes: biases from neglecting light-cone effects

2021 ◽  
Vol 2021 (12) ◽  
pp. 004
Author(s):  
Jan-Albert Viljoen ◽  
José Fonseca ◽  
Roy Maartens
Keyword(s):  
Light Cone ◽  
Cosmological Parameters ◽  
Relativistic Effects ◽  
Companion Paper ◽  
Galaxy Surveys ◽  
Intensity Mapping ◽  
Spectroscopic Probes ◽  
Multi Wavelength ◽  
Access Information ◽  
Best Fit

Abstract Next-generation cosmological surveys will observe larger cosmic volumes than ever before, enabling us to access information on the primordial Universe, as well as on relativistic effects. In a companion paper, we applied a Fisher analysis to forecast the expected precision on f NL and the detectability of the lensing magnification and Doppler contributions to the power spectrum. Here we assess the bias on the best-fit values of f NL and other parameters, from neglecting these light-cone effects. We consider forthcoming 21cm intensity mapping surveys (SKAO) and optical galaxy surveys (DESI and Euclid), both individually and combined together. We conclude that lensing magnification at higher redshifts must be included in the modelling of spectroscopic surveys. If lensing is neglected in the analysis, this produces a bias of more than 1σ — not only on f NL, but also on the standard cosmological parameters.

One-Electron Atoms

2007 ◽  
Author(s):  
Kenneth G. Dyall ◽  
Knut Faegri
Keyword(s):  
Dirac Equation ◽  
Schrödinger Equation ◽  
Quantum Chemistry ◽  
Schrodinger Equation ◽  
Relativistic Quantum ◽  
Relativistic Effects ◽  
Energy Scale ◽  
Basis Functions ◽  
Nonrelativistic Case ◽  
Relativistic Quantum Chemistry

The development of quantum chemistry, that is, the solution of the Schrödinger equation for molecules, is almost exclusively founded on the expansion of the molecular electronic wave function as a linear combination of atom-centered functions, or atomic orbitals—the LCAO approximation. These orbitals are usually built up out of some set of basis functions. The properties of the atomic functions at large and small distances from the nucleus determines to a large extent what characteristics the basis functions must have, and for this purpose it is sufficient to examine the properties of the hydrogenic solutions to the Schrödinger equation. If we are to do the same for relativistic quantum chemistry, we should first examine the properties of the atomic solutions to determine what kind of basis functions would be appropriate. However, the atomic solutions of the Dirac equation provide more than merely a guide to the choice of basis functions. The atoms in a molecule retain their atomic identities to a very large extent, and the modifications caused by the molecular field are quite small for most properties. In order to arrive at a satisfactory description of the relativistic effects in molecules, we must first of all be able to treat these effects at the atomic level. The insight gained into the effects of relativity on atomic structure is therefore a necessary and useful starting point for relativistic quantum chemistry. As in the nonrelativistic case, most of the salient features of the atomic systems are exposed in the treatment of the simplest of these, the hydrogen-like one-electron atoms. In Hartree atomic units the time-independent Dirac equation yields the coupled equations where we have shifted the energy by −mc2 (with m = 1), as discussed in section 4.6. We will use this shifted energy scale for the rest of the book unless otherwise explicitly indicated. V is here a scalar, central potential.

scholarly journals Helical Motion and Non-Adiabatic Expansion in the Jet of 3C345

1994 ◽  
Vol 159 ◽  
pp. 432-432
Author(s):  
W. Steffen ◽  
T.P. Krichbaum ◽  
A. Witzel ◽  
J.A. Zensus ◽  
S.J. Qian
Keyword(s):  
Flux Density ◽  
Inhomogeneous Plasma ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Helical Motion ◽  
Adiabatic Expansion ◽  
Density Evolution ◽  
Differential Doppler ◽  
Expansion Model ◽  
Jet Axis

We developed a kinematic jet model for the motion and flux density evolution of the high frequency VLBI jet components C4 and C5 in the quasar 3C345 (Zensus et al. 1994) assuming the conservation of three basic quantities: the Lorentz factor, the angular momentum, and the opening angle of the jet. This model is a simplified description of the helical motion in a conical jet expected from the magnetodynamical model of Camenzind (1986) which is based on a black hole surrounded by a magnetized accretion disc. Our best fit yields Lorentz factors of 5.7 and 5.0 for components C4 and C5, respectively, and an angle between the jet axis and the observer's line of sight of 7.5°. These values are very close to those obtained by Unwin & Wehrle (1992) from component motion further out. An intrinsic bending of the jet axis is necessary to account for the common bent path of all jet components at core separations larger than about 4 mas. We found that differential Doppler boosting alone is not able to explain the flux density variations of component C4. A non-adiabatic expansion model of an inhomogeneous plasma cloud combined with differential Doppler boosting on a helical path fits the flux density evolution (Steffen et al. 1994). We find that the expansion in the decreasing part of the lightcurve is slower than expected from adiabatic expansion.

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