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.

Flux density evolution of the sources 3C273, 3C279 and 3C454.3 at the frequencies 102 MHz–36.8 GHz

2006 ◽  
Vol 25 (5-6) ◽  
pp. 385-391 ◽  
Author(s):  
A. E. Volvach ◽  
L. N. Volvach ◽  
M. G. Larionov ◽  
H. D. Aller ◽  
M. F. Aller ◽  
...  
Keyword(s):  
Flux Density ◽  
Density Evolution

MOLECULAR DYNAMICS SIMULATION OF PULSED LASER ABLATION

2011 ◽  
Vol 25 (04) ◽  
pp. 543-550 ◽  
Author(s):  
XIU-FANG GONG ◽  
GONG-XIAN YANG ◽  
PENG LI ◽  
YIN WANG ◽  
XI-JING NING
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Laser Pulses ◽  
Solid Surfaces ◽  
Dynamics Simulation ◽  
Angular Distributions ◽  
Adiabatic Expansion ◽  
Expansion Model

We have developed a simplified molecular-dynamical model for simulating ablation of solid surfaces by laser pulses, and specifically investigated expansion of Cu cloud in vacuum vaporized on the surface, showing that the angular distributions of the plume depend on the shape of the laser spot on the surface. In particular, experimentally observed flipover effects have been obtained, and an adiabatic constant determined from our simulations via an adiabatic expansion model agrees well with previous measurements.

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 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 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 Tests for a Relativistic Beaming Model Using a VLBI Survey

1988 ◽  
Vol 129 ◽  
pp. 79-80
Author(s):  
Makoto Inoue
Keyword(s):  
Flux Density ◽  
Statistical Study ◽  
Lorentz Factor ◽  
Radio Galaxies ◽  
High Frequencies ◽  
Relativistic Beaming

We have examined a relativistic beaming model using a VLBI survey by Preston et al. (1985). Our statistical study of a ratio R of the flux density for the beamed compact core to that for unbeamed components of a source shows Lorentz factor γ to be ≅ 6 and RT (R at transverse alignment) to be ≅ 10−2 for a sample of 222 QSO's. In addition, we find that a sample of 60 radio galaxies show the beaming effect with γ ≅ 4. It should be emphasized here that the beaming effect strongly affects the source counts (Log N - Log S) especially at high frequencies.

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 Radio outburst from a massive (proto)star

2018 ◽  
Vol 612 ◽  
pp. A103 ◽  
Author(s):  
R. Cesaroni ◽  
L. Moscadelli ◽  
R. Neri ◽  
A. Sanna ◽  
A. Caratti o Garatti ◽  
...  
Keyword(s):  
Flux Density ◽  
Mass Loss Rate ◽  
Strong Support ◽  
Stellar Object ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Opening Angle ◽  
Very Large Array ◽  
Young Stellar Object ◽  
Radio Outburst

Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in both methanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst, possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be common in young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the star may occur in a non-continuous way. Aims. As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretion interpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet. Methods. We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. Jansky Very Large Array. The millimetre continuum emission was also observed with both the Northern Extended Millimeter Array of IRAM and the Atacama Large Millimeter/Submillimeter Array. Results. We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July 10, 2016, namely ~13 months after the estimated onset of the IR outburst. This is the first ever detection of a radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observed centimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginal flux increase with respect to the literature values and we show this is due to free–free emission from the radio jet. Conclusions. Our model fits indicate a significant increase in the jet opening angle and ionized mass loss rate with time. For the first time, we can estimate the ionization fraction in the jet and conclude that this must be low (<14%), lending strong support to the idea that the neutral component is dominant in thermal jets. Our findings strongly suggest that recurrent accretion + ejection episodes may be the main route to the formation of massive stars.

scholarly journals Electron cooling and the connection between expansion and flux-density evolution in radio supernovae

2011 ◽  
Vol 529 ◽  
pp. A47 ◽  
Author(s):  
I. Martí-Vidal ◽  
M. A. Pérez-Torres ◽  
A. Brunthaler
Keyword(s):  
Flux Density ◽  
Electron Cooling ◽  
Density Evolution

scholarly journals Radio Structures of the MRC 1-Jy Sources and the Unification of Radio Galaxies and Quasars

1996 ◽  
Vol 175 ◽  
pp. 393-394
Author(s):  
V. K. Kapahi ◽  
R. M. Athreya ◽  
C. R. Subrahmanya ◽  
P. J. Mccarthy ◽  
W. Van BREUGEL ◽  
...  
Keyword(s):  
Low Frequency ◽  
Radio Galaxies ◽  
Line Of Sight ◽  
Opening Angle ◽  
Viewing Angle ◽  
Radio Luminosity ◽  
Redshift Range ◽  
Statistical Studies ◽  
Quasars And Radio Galaxies ◽  
Jet Axis

The viewing angle of ≃45° (between the jet axis and the line of sight) dividing quasars and radio galaxies in the orientation-based unified scheme (Barthel 1989) is based largely on the observation that in the redshift range of 0.5 < z < 1.0 in the low-frequency 3CRR sample, there are about twice as many radio galaxies than quasars and the median linear size of galaxies is about twice that of the quasars. The relative numbers and sizes of quasars in other redshift ranges in the 3CRR are however in conflict with the simple unified scheme even if the opening angle is considered to evolve with epoch or radio luminosity (Kapahi 1990; Singal 1993). Larger sources samples, preferably selected at low radio frequencies, are clearly important in such statistical studies.

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