Jet Energy Flux Research Articles

The chemical signature of jet-driven hypernovae

ABSTRACT Hypernovae powered by magnetic jets launched from the surface of rapidly rotating millisecond magnetars are one of the leading models to explain broad-lined Type Ic supernovae (SNe Ic-BL), and have been implicated as an important source of metal enrichment in the early Universe. We investigate the nucleosynthesis in such jet-driven hypernovae using a parametrized, but physically motivated, approach that analytically relates an artificially injected jet energy flux to the power available from the energy in differential rotation in the protoneutron star. We find ejected 56Ni masses of $0.05\, \!-\!0.45\, \mathrm{M}_\odot$ in our most energetic models with explosion energy $\gt 10^{52}\, \mathrm{erg}$. This is in good agreement with the range of observationally inferred values for SNe Ic-BL. The 56Ni is mostly synthesized in the shocked stellar envelope, and is therefore only moderately sensitive to the jet composition. Jets with a high electron fraction Ye = 0.5 eject more 56Ni by a factor of 2 than neutron-rich jets. We can obtain chemical abundance profiles in good agreement with the average chemical signature observed in extremely metal-poor (EMP) stars presumably polluted by hypernova ejecta. Notably, [Zn/Fe] ≳ 0.5 is consistently produced in our models. For neutron-rich jets, there is a significant r-process component, and agreement with EMP star abundances in fact requires either a limited contribution from neutron-rich jets or a stronger dilution of r-process material in the interstellar medium than for the slow SN ejecta outside the jet. The high [C/Fe] ≳ 0.7 observed in many EMP stars cannot be consistently achieved due to the large mass of iron in the ejecta, however, and remains a challenge for jet-driven hypernovae based on the magnetorotational mechanism.

Ultrahigh energy cosmic rays from shocks in the lobes of powerful radio galaxies

The origin of ultra-high energy cosmic rays (UHECRs) has been an open question for decades. Here, we use a combination of hydrodynamic simulations and general physical arguments to demonstrate that UHECRs can in principle be produced by diffusive shock acceleration (DSA) in shocks in the backflowing material of radio galaxy lobes. These shocks occur after the jet material has passed through the relativistic termination shock. Recently, several authors have demonstrated that highly relativistic shocks are not effective in accelerating UHECRs. The shocks in our proposed model have a range of non-relativistic or mildly relativistic shock velocities more conducive to UHECR acceleration, with shock sizes in the range 1-10kpc. Approximately 10% of the jet's energy flux is focused through a shock in the backflow of $M>3$. Although the shock velocities can be low enough that acceleration to high energy via DSA is still efficient, they are also high enough for the Hillas energy to approach $10^{19-20}$eV, particularly for heavier CR composition and in cases where fluid elements pass through multiple shocks. We discuss some of the more general considerations for acceleration of particles to ultra-high energy with reference to giant-lobed radio galaxies such as Centaurus A and Fornax A, a class of sources which may be responsible for the observed anisotropies from UHECR observatories.

Ideal engine durations for gamma-ray-burst-jet launch

Aiming to study GRB engine duration, we present numerical simulations to investigate collapsar jets. We consider typical explosion energy ($10^{52}$ erg) but different engine durations, in the widest domain to date from 0.1 to 100 s. We employ an AMR 2D hydrodynamical code. Our results show that engine duration strongly influences jet nature. We show that the efficiency of launching and collimating relativistic outflow increases with engine duration, until the intermediate engine range where it is the highest, past this point to long engine range, the trend is slightly reversed; we call this point where acceleration and collimation are the highest "sweet spot" ($\sim$10 -- 30 s). Moreover, jet energy flux shows that variability is also high in this duration domain. We argue that not all engine durations can produce the collimated, relativistic and variable long GRB-jets. Considering a typical progenitor and engine energy, we conclude that the ideal engine duration to reproduce a long GRB is $\sim$10 -- 30 s, where the launch of relativistic, collimated and variable jets is favored. We note that this duration domain makes a good link with Lazzati et al. (2013), which suggested that the bulk of BATSE's long GRBs is powered by $\sim$10 -- 20 s collapsar engines.

TIME-DEPENDENT MODELING OF GAMMA-RAY FLARES IN BLAZAR PKS1510–089

Here we present a new approach for constraining luminous blazars, incorporating fully time-dependent and self-consistent modeling of bright gamma-ray flares of PKS1510-089 resolved with Fermi-LAT, in the framework of the internal shock scenario. The results of our modeling imply the location of the gamma-ray flaring zone outside of the broad-line region, namely around 0.3pc from the core for a free-expanding jet with the opening angle Gamma, \theta_\mathrm{jet} \simeq 1 (where Gamma is the jet bulk Lorentz factor), up to \simeq 3pc for a collimated outflow with Gamma, \theta_\mathrm{jet} \simeq 0.1. Moreover, under the Gamma, \theta_\mathrm{jet} \simeq 1 condition, our modeling indicates the maximum efficiency of the jet production during the flares, with the total jet energy flux strongly dominated by protons and exceeding the available accretion power in the source. This is in contrast to the quiescence states of the blazar, characterized by lower jet kinetic power and an approximate energy equipartition between different plasma constituents. We demostrate how strictly simultaneous observations of flaring PKS1510-089 at optical, X-ray, and GeV photon energies on hourly timescales, augmented by extensive simulations as presented in this paper, may help to impose further precise constraints on the magnetization and opening angle of the emitting region. Our detailed modeling implies in addition that a non-uniformity of the Doppler factor across the jet, caused by the radial expansion of the outflow, may lead to a pronounced time distortion in the observed gamma-ray light curves, resulting in particular in asymmetric flux profiles with substantially extended decay phases.

The physical parameters of the microquasar S26 in the Sculptor Group galaxy NGC 7793

NGC 7793 - S26 is an extended source (350 pc $\times$ 185 pc) previously studied in the radio, optical and x-ray domains. It has been identified as a micro-quasar which has inflated a super bubble. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to analyse spectra between 3600--7000 \AA. This allowed us to derive fluxes and line ratios for selected nebular lines. Applying radiative shock model diagnostics, we estimate shock velocities, densities, radiative ages and pressures across the object. We show that S26 is just entering its radiative phase, and that the northern and western regions are dominated by partially-radiative shocks due to a lower density ISM in these directions. We determine a velocity of expansion along the jet of 330 km s$^{-1}$, and a velocity of expansion of the bubble in the minor axis direction of 132 km s$^{-1}$. We determine the age of the structure to be $4.1\times10^5$ yr, and the jet energy flux to be $ (4-10)\times10^{40}$ erg s$^{-1}$ The jet appears to be collimated within $\sim0.25$ deg, and to undergo very little precession. If the relativistic $\beta \sim 1/3$, then some 4 M$_{\odot}$ of relativistic matter has already been processed through the jet. We conclude that the central object in S26 is probably a Black Hole with a mass typical of the ultra-luminous X-ray source population which is currently consuming a fairly massive companion through Roche Lobe accretion.

Magnetic domination of recollimation boundary layers in relativistic jets

We study the collimation of relativistic magnetohydrodynamic jets by the pressure of an ambient medium, in the limit where the jet interior loses causal contact with its surroundings. This follows up a hydrodynamic study in a previous paper, adding the effects of a toroidal magnetic field threading the jet. As the ultrarelativistic jet encounters an ambient medium with a pressure profile with a radial scaling of p ~ r^-eta where 2<eta<4, it loses causal contact with its surroundings and forms a boundary layer with a large pressure gradient. By constructing self-similar solutions to the fluid equations within this boundary layer, we examine the structure of this layer as a function of the external pressure profile. We show that the boundary layer always becomes magnetically dominated far from the source, and that in the magnetic limit, physical self-similar solutions are admitted in which the total pressure within the layer decreases linearly with distance from the contact discontinuity inward. These solutions suggest a `hollow cone' behavior of the jet, with the boundary layer thickness prescribed by the value of eta. In contrast to the hydrodynamical case, however, the boundary layer contains an asymptotically vanishing fraction of the jet energy flux.

Linkage between accretion disks and blazars

The magnetic field in an accretion disk is estimated assuming that all of the angular momentum within prescribed accretion disk radii is removed by a jet. The magnetic field estimated at the base of the jet is extrapolated to the blazar emission region using a model for a relativistic axisymmetric jet combined with some simplifying assumptions based on the relativistic nature of the flow. The extrapolated magnetic field is compared with estimates based upon the synchrotron and inverse Compton emission from three blazars, MKN 501, MKN 421 and PKS 2155-304. The magnetic fields evaluated from pure synchrotron self-Compton models are inconsistent with the magnetic fields extrapolated in this way. However, in two cases inverse Compton models in which a substantial part of the soft photon field is generated locally agree well, mainly because these models imply magnetic field strengths consistent with an important Poynting Flux component. This comparison is based on estimating the mass accretion rate from the jet energy flux. Further comparisons along these lines will be facilitated by independent estimates of the mass accretion rate in blazars and by more detailed models for jet propagation near the black hole.

Magnetic field amplification in FR II hotspots

A key assumption is some models of radio source evolution is that the magnetic field in the hotspots is always equal to the equipartition value and that this value is proportional to the jet energy flux. This assumption is tested by following the evolution of the magnetic field in the turbulent hotspot flow via a series of three dimensional, time dependent and fully nonlinear calculations of MHD turbulence in the hotspots. Turbulent amplification of the magnetic field is examined for a variety of energy spectra that might occur in the hotspots. It is found that equipartition is reached in the time required only for a subset of possible initial conditions and only reliably on the smallest turbulent scales. Amplification to equipartition on all turbulent scales usually takes 30 or more large scale eddy turnover times, and this time may well exceed the dwell time of the fluid in the hotspot unless special conditions are imposed.

Asymmetries in the jets of weak radio galaxies

We describe a study of the side-to-side asymmetries on kpc scales in the jets of FR I radio galaxies selected from the B2 sample. The basic data are jet surface brightnesses and widths determined by fitting transverse profiles to Very Large Array (VLA) images at a range of distances from the core. Differences between the jets at a given distance from the nucleus are interpreted as effects of Doppler beaming on intrinsically symmetrical flows and are compared with the model derived for 3C31 by Laing & Bridle and with simpler variants. The jet/counterjet brightness ratios where the main jet first brightens are correlated with core prominence, as expected for a relativistic flow. From the distribution of brightness ratios, we infer that jets have a maximum velocity ≈0.9c where they first flare and brighten, but there is also evidence for additional slower material. Deceleration to subrelativistic speeds occurs on scales which increase with radio power. Jets in the majority of sources with luminosities <1024 WHz-1 at 1.4 GHz become essentially symmetrical (and therefore subrelativistic) within 2 kpc of the core. In more powerful sources, jets that flare within the first 2 kpc become symmetrical by 10 kpc, but a subset of the most luminous objects has jets which remain asymmetrical to larger distances. The point at which the brighter jet flares appears to correspond to a sudden increase in rest-frame emissivity, but the ratio of distances to the flaring point in main and counterjets is anticorrelated with brightness ratio, as expected for a decelerating relativistic flow. Brightness and full width at half-maximum (FWHM) ratios are also anticorrelated, an effect which we interpret as a result of Doppler beaming for a flow in which the velocity decreases radially outwards from the jet axis. Jet deceleration by entrainment of external material provides a natural explanation for these velocity gradients. The jet energy flux is roughly consistent with energy supply to the lobes over a source lifetime estimated from spectral index measurements. Our results are qualitatively consistent with unified models of FR I radio galaxies and BL Lac objects, but require some modifications to the standard picture.

Are Seyfert Narrow‐Line Regions Powered by Radio Jets?

We argue that the narrow line regions of Seyfert galaxies are powered by the transport of energy and momentum by the radio-emitting jets and consequently that the ratio of the radio power to jet energy flux is much smaller than is usually assumed for radio galaxies. This can be partially attributed to the smaller ages ($\sim 10^6 yrs$) of Seyferts compared to radio galaxies but one also requires that either the magnetic energy density is more than an order of magnitude below the equipartition value, or more likely, that the internal energy densities of Seyfert jets are dominated by thermal plasma. If Seyfert jets are initially dominated by relativistic plasma, then an analysis of the data on jets in five Seyfert galaxies shows that all but one of these would have mildly relativistic jet velocities near 100 pc in order to power the respective narrow-line regions. However, observations of jet-cloud interactions in the NLR provide additional information on jet velocities and composition via the momentum budget. Our analysis of a jet-cloud interaction in NGC 1068, implies a shocked jet pressure much larger than the minimum pressure of the radio knot, a velocity $\sim 0.06 c$ and a jet temperature $\sim 10^9 K$ implying mildly relativistic electrons but thermal protons. The jet mass flux at this point $\sim 0.5 M_\odot yr^{-1}$, is an order of magnitude higher than the mass accretion rate into the black hole, strongly indicating entrainment. The initial jet mass flux $\sim 0.02 M_\odot yr^{-1}$, comparable to the mass accretion rate and is consistent with the densities inferred for accretion disc coronae from high energy observations, together with an initially mildly relativistic velocity and an initial jet radius of order 10 gravitational radii.

Relativistic Jets and the Fanaroff-Riley Classification of Radio Galaxies

view Abstract Citations (190) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relativistic Jets and the Fanaroff-Riley Classification of Radio Galaxies Bicknell, Geoffrey V. Abstract Recently, Owen and Owen & Ledlow have shown that the dividing line between Fanaroff-Riley class I and class II radio sources is very sharp when the sources are represented as points in the radio-optical luminosity plane. A theoretical expression for the dividing line is derived on the basis that borderline class I/II sources are characterized by (1) transonic Mach numbers and (2) more or less unique (~0.6 c) mildly relativistic velocities, consistent with deceleration of an initially moderately relativistic or ultrarelativistic jet. The deduction of a unique transonic velocity is combined with established empirical relationships between the X-ray luminosities, core radii, velocity dispersions, and absolute magnitudes of elliptical galaxies. The slope of the theoretical dividing line is well determined and agrees well with that inferred from the data. The intercept of the dividing line depends upon several parameters which are known perhaps to within factors of order unity and agrees with the data to better than an order of magnitude. As a corollary to this work, useful relationships between the source total and monochromatic luminosities and the jet energy flux are obtained. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1995 DOI: 10.1086/192232 arXiv: arXiv:astro-ph/9406064 Bibcode: 1995ApJS..101...29B Keywords: GALAXIES: JETS; GALAXIES: STRUCTURE; X-RAYS: GALAXIES; Astrophysics E-Print: uuencoded, compressed postscript, MSSS0 999 full text sources arXiv | ADS | data products SIMBAD (2)