Conical Jet Model Research Articles

Cosmological investigation of multi-frequency VLBI observations of ultra-compact structure in zsim 3 radio quasars

In this paper, we use multi-frequency angular size measurements of 58 intermediate-luminosity quasars reaching the redshifts zsim 3 and demonstrate that they can be used as standard rulers for cosmological inference. Our results indicate that, for the majority of radio-sources in our sample their angular sizes are inversely proportional to the observing frequency. From the physical point of view it means that opacity of the jet is governed by pure synchrotron self-absorption, i.e. external absorption does not play any significant role in the observed angular sizes at least up to 43 GHz. Therefore, we use the value of the intrinsic metric size of compact milliarcsecond radio quasars derived in a cosmology independent manner from survey conducted at 2 GHz and rescale it properly according to predictions of the conical jet model. This approach turns out to work well and produce quite stringent constraints on the matter density parameter Omega _m in the flat Lambda CDM model and Dvali–Gabadadze–Porrati braneworld model. The results presented in this paper pave the way for the follow up engaging multi-frequency VLBI observations of more compact radio quasars with higher sensitivity and angular resolution.

Study on the Properties of Blazar Jets

The multi-wavelength quasi-simultaneous data of 55 Fermi blazars are fitted by using the conical jet model, and the physical properties of blazar jets are also investigated. Through the X2-minimization fitting procedure, the best-fit parameters of the conical jet model are obtained. Combined with the other parameters we collected, a statistical analysis is performed. The results of statistical analysis are summarized as follows: (1) The jet power obtained by the spectral energy distribution (SED) fitting is larger than the jet power calculated by using the extended radio luminosity; (2) There is no correlation between the Doppler factor 5 and the magnetic field strength B; (3) There is a correlation between the jet power and the accretion disk luminosity, and the Blandford-Znajek (BZ) mechanism can well explain the energy source of BL Lac jets rather than Flat Spectrum Radio Quasars (FSRQs); (4) The jet power is significantly correlated with the black hole mass.

HIGH-PRECISION ASTROMETRIC MILLIMETER VERY LONG BASELINE INTERFEROMETRY USING A NEW METHOD FOR MULTI-FREQUENCY CALIBRATION

ABSTRACT In this paper we describe a new approach for millimeter Very Long Baseline Interferometry (mm-VLBI) calibration that provides bona-fide astrometric alignment of the millimeter-wavelength images from a single source, for the measurement of frequency-dependent effects, such as “core-shifts” near the black hole of active galactic nucleus jets. We achieve our astrometric alignment by solving first for the ionospheric (dispersive) contributions using wide-band centimeter-wavelength observations. Second, we solve for the tropospheric (non-dispersive) contributions by using fast frequency-switching at the target millimeter-wavelengths. These solutions can be scaled and transferred from low frequency to the high frequency. To complete the calibration chain an additional step is required to remove a residual constant phase offset on each antenna. The result is an astrometric calibration and the measurement of the core-shift between 22 and 43 GHz for the jet in BL Lacertae to be −8 ± 5, 20 ± 6 μas, in R.A. and decl., respectively. By comparison to conventional phase referencing at centimeter-wavelengths we are able to show that this core shift at millimeter-wavelengths is significantly less than what would be predicted by extrapolating the low-frequency result, which closely followed the predictions of the Blandford & Königl conical jet model. As such it would be the first demonstration for the association of the VLBI core with a recollimation shock, normally hidden at low frequencies due to the optical depth, which could be responsible for the γ-ray production in blazar jets.

MINUTE-TIMESCALE >100 MeV γ-RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI-LAT IN 2015 JUNE

ABSTRACT On 2015 June 16, Fermi-LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak >100 MeV flux of ∼3.6 × 10−5 photons cm−2 s−1, averaged over orbital period intervals. It is historically the highest γ-ray flux observed from the source, including past EGRET observations, with the γ-ray isotropic luminosity reaching ∼1049 erg s−1. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 minutes, was operated in a special pointing mode to optimize the exposure for 3C 279. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi-LAT. The source flux variability was resolved down to 2-minute binned timescales, with flux doubling times of less than 5 minutes. The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models. A minimum bulk jet Lorentz factor (Γ) of 35 is necessary to avoid both internal γ-ray absorption and super-Eddington jet power. In the standard external radiation Comptonization scenario, Γ should be at least 50 to avoid overproducing the synchrotron self-Compton component. However, this predicts extremely low magnetization (∼5 × 10−4). Equipartition requires Γ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider γ rays originating as synchrotron radiation of γ e ∼ 1.6 × 106 electrons, in a magnetic field B ∼ 1.3 kG, accelerated by strong electric fields E ∼ B in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude the production of γ-rays in hadronic processes.

Modelling the multi-wavelength emission of flat-spectrum radio quasar 3C 279

We employ a length-dependent conical jet model for the jet structure and emission properties of flat-spectrum radio quasar 3C 279 in the steady state. In the model, ultra-relativistic leptons are injected at the base of the jet and propagate along the jet structure. Non-thermal photons are produced by both synchrotron emission and inverse Compton scattering off synchrotron photons and external soft photons at each segment of the jet. We derive the total energy spectra contribution through integrating every segment. We apply the model to the quasi-simultaneous multi-wavelength observed data of two quiescent epochs. Using the observed radio data of the source, we determine the length of the jet L ∼ 100 pc and the magnetic field B0 ∼ 0.1–1 G at the base of the jet. Assuming a steady geometry of the jet structure and suitable physical parameters, we reproduce the multi-wavelength spectra during two quiescent observed epochs. Our results show that the initial γ-ray emission site is ∼0.5 pc from the black hole.

Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources

We have measured the angular sizes of radio cores of active galactic nuclei (AGN) and analyzed their sky distributions and frequency dependencies to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, $\nu$, from 2 to 43 GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane ($|b|\lesssim10^\circ$) at 2, 5 and 8 GHz, about 1/3 of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region, and a region with galactic longitudes $220^\circ\lesssim l\lesssim260^\circ$ (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic H$\alpha$ intensity, free-electron density, and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr A$^\ast$ is found to be the largest among thousands of AGN observed over the sky; we discuss possible reasons of this strange result. Excluding extragalactic radio sources with significant scattering, we find that angular size of opaque cores in AGN scales typically as $\nu^{-1}$ confirming predictions of a conical synchrotron jet model with equipartition.

An Inhomogeneous Jet Model and Its Application in BL Lacertae Objects

In the inhomogeneous conical jet model, the electron number den- sity and magnetic field strength have a power-law distribution with the distance from the jet apex. This model can interpret successfully the flat-spectrum radio radiation from the core regions of active galactic nuclei. But the existing model calculation suits only the situation when the enclosed angle between the moving direction of a jet and the line of sight is very large, hence, we need to build a formula for calculating the radiation of inhomogeneous conical jets with any viewing angles. It is generally believed that the enclosed angle between the di- rection of jet motion and the line of sight is very small in BL Lac objects. With the extended inhomogeneous jet model, we have made fitting on the observed radio spectra of three BL Lac objects, and obtained the physical parameters, such as the electron number density and magnetic field strength in their jets. The result indicates that the nearest distance of the conical jet from the black hole is determined by the transition frequency of the observed radiation spec- trum, and that the nearest distance between the conical jet and the black hole is approximately the Schwarzschild radius for the three BL Lac objects.

Jets and the accretion flow in low-luminosity black holes

The X-ray spectra of black hole binaries in the low/hard state first harden as the flux decreases, then soften. This change in behaviour has been variously attributed to either the X-rays switching from being produced in the flow to being dominated by the jet, or to the flow switching seed photons from the disc to self generated seed photons from cyclo-synchrotron. Here we build a simple truncated disc, hot inner flow, plus standard conical synchrotron jet model to explore what this predicts for the X-ray emission mechanism as a function of mass accretion rate. We find that the change in X-ray spectral index can be quantitatively (not just qualitatively) explained by the seed photon switch in the hot flow i.e. this supports models where the X-rays are always produced by the hot flow. By contrast, standard conical jet models are as radiatively inefficient as the hot flow so there is no transition in X-ray production mechanism with $\dot{m}$. Including the effects of electron cooling allows the jet X-rays to drop more slowly with accretion rate and hence overtake the X-rays from the hot flow, however this produces a corresponding change in the radio-X-ray correlation, which is not observed. We argue that the unbroken radio-X-ray correlation down to quiescence rules out the jet transition model as an explanation for the trend in X-ray spectral index. Our favoured model is then a truncated disc with an inner, hot, radiatively inefficient flow which always dominates the hard X-rays, coupled to a conical synchrotron jet which produces the radio emission. However, even this has issues at low $\dot{m}$ as the low optical depth and high temperature of the flow means that the Compton spectrum is not well approximated by a power law. This shows the need for a more sophisticated model for the electron distribution in the hot flow.

Synchrotron and inverse-Compton emission from blazar jets - I. A uniform conical jet model

In the first of a series of papers investigating emission from blazar jets from radio to high-energy {\gamma}-rays, we revisit the class of models where the jet has a uniform conical ballistic structure. We argue that by using simple developments of these models, in the context of new multi-frequency data extending to gamma-ray energies, valuable insights may be obtained into the properties that fully realistic models must ultimately have. In this paper we consider the synchrotron and synchrotron-self-Compton emission from the jet, modelling the recent simultaneous multi-wavelength observations of BL Lac. This is the first time these components have been fitted simultaneously for a blazar using a conical jet model. In the model we evolve the electron population dynamically along the jet taking into account the synchrotron and inverse-Compton losses. The inverse-Compton emission is calculated using the Klein-Nishina cross section and a relativistic transformation into the jet frame, and we explicitly show the seed photon population. We integrate synchrotron opacity along the line of sight through the jet plasma, taking into account the emission and opacity of each section of the jet. In agreement with previous studies of radio emission, we find that a conical jet model which conserves magnetic energy produces the characteristic blazar flat radio spectrum, however, we do not require any fine-tuning of the model to achieve this. Of particular note, in our model fit to BL Lac--which at ~10^37W is a relatively low jet-power source--we find no requirement for significant re-acceleration within the jet to explain the observed spectrum.

Multifrequency emission analysis of TeV blazars H 2356–309 and 1ES 1218+304

The multiband nonthermal emissions in radio, X-ray, and very high-energy (VHE) γ-ray bands from two distant blazars, H 2356–309 and 1ES 1218+304, have been detected, and, especially from recent observations with the Suzaku, MAGIC and VERITAS telescopes, clearly reveal nonthermal power-law spectra. We study the broadband nonthermal spectra of the two sources by using a combination of a one-zone homogeneous synchrotron self-Compton (SSC) model and an inhomogeneous conical jet model, where the new external background light (EBL) model is taken into account. The results show that (1) the nonthermal emissions of the two blazars, ranging from X-rays to VHE γ-rays, are from the homogeneous zone whereas the emissions in the radio bands can be explained as the radiation from the inhomogeneous conical jet; (2) a strict lower-limit EBL model can be used to explain their observed spectra well.

Magnetic field strength and spectral distribution of six parsec-scale active galactic nuclei jets

We use observations of six "blazars" with the Very Long Baseline Array (VLBA), at eight frequencies (4.6, 5.1, 7.9, 8.9, 12.9, 15.4, 22.2, 43.1 GHz), to investigate the frequency-dependent position of their VLBI cores ("core-shift") and their overall jet spectral distribution. By cross-correlating the optically thin jet emission, we are able to accurately align the multi-frequency images of three of the jets (1418+546, 2007+777, 2200+420), whose core-shifts and spectra we find consistent with the equipartition regime of the Blandford & Konigl conical jet model, where the position of the radio core from the base of the jet follows $r_{core}\propto\nu^{-1}$. For the jet of 0954+658, we align the higher frequency images using our lower frequency measurements assuming equipartition in the radio core from 4.6-43 GHz. The jet emission of the other two sources in our sample (1156+295, 1749+096) is too sparse for our alignment technique to work. Using our measured core-shifts, we calculate equipartition magnetic field strengths of the order of 10's to 100's of mG in the radio cores of these four AGN from 4.6-43 GHz. Extrapolating our results back to the accretion disk and black hole jet-launching distances, we find magnetic field strengths consistent with those expected from theoretical models of magnetically powered jets.

GMRT Observations of Microquasar V4641 Sgr

We report the GMRT observations of V4641 Sgr during the May 2002 outburst at radio frequencies of 610 and 244 MHz. This is the lowest frequency radio detection of this source. The present low frequency radio observations clearly showed spectral evolution from the optically thick to thin state. This behavior is broadly consistent with the expanding bubble model. However, the flux densities observed at lower frequencies are much higher than predicted by this model. In the conical jet model, this discrepancy could be reconciled.

Effect of Conversion Efficiency on Gamma-Ray Burst Energy

Beaming effect makes it possible that gamma-ray bursts have a standard energy, but the gamma-ray energy release is sensitive to some parameters. Our attention is focused on the effect of the gamma ray conversion efficiency ( eta γ ), which may range between 0.01 and 0.9, and which probably has a random value for different GRBs under certain conditions. Making use of the afterglow data from the literature, we carried out a complete correction to the conical opening angle formula. Within the framework of the conical jet model, we ran a simple Monte Carlo simulation for random values of eta γ , and found that the gamma-ray energy release is narrowly clustered, whether we use a constant value of eta γ or random values for different gamma-ray bursts.

Quasi-universal Gaussian Jets: A Unified Picture for Gamma-Ray Bursts and X-Ray Flashes

An observed correlation Ep ∝ (Eiso)1/2 extending from gamma-ray bursts (GRBs) to X-ray flashes (XRFs) poses problems both for a power-law universal jet model, in which the energy per solid angle decreases as the inverse square of the angle with respect to the jet axis, and for a conical jet model with a uniform energy density within the jet beam and a sharp energy cutoff at the jet edge. Here we show that the current GRB-XRF prompt emission/afterglow data can be understood in terms of a picture in which the GRB-XRF jets are quasi-universal and structured, with a Gaussian-like or similar structure, i.e., one where the jet has a characteristic angle, with a mild variation of energy inside and a rapid (e.g., exponential) decrease of energy outside of it. A Monte Carlo simulation shows that the current data is compatible with such a quasi-universal Gaussian jet with a typical opening angle of 5.7 deg and with a standard jet energy of about log(Ej/1 erg) = 51.1 ± 0.3. According to this model, the true-to-observed number ratio of the whole GRB-XRF population is about 14 with the current instrumental sensitivity.

Gamma‐Ray Burst Energetics and the Gamma‐Ray Burst Hubble Diagram: Promises and Limitations

We present a complete sample of 29 gamma-ray bursts (GRBs) for which it has been possible to determine temporal breaks (or limits) from their afterglow light curves. We interpret these breaks within the framework of the uniform conical jet model, incorporating realistic estimates of the ambient density and propagating error estimates on the measured quantities. In agreement with our previous analysis of a smaller sample, the derived jet opening angles of those 16 bursts with redshifts result in a narrow clustering of geometrically corrected gamma-ray energies about γ = 1.33 × 1051 ergs; the burst-to-burst variance about this value is 0.35 dex, a factor of 2.2. Despite this rather small scatter, we demonstrate in a series of GRB Hubble diagrams that the current sample cannot place meaningful constraints upon the fundamental parameters of the universe. Indeed, for GRBs to ever be useful in cosmographic measurements, we argue the necessity of two directions. First, GRB Hubble diagrams should be based upon fundamental physical quantities such as energy, rather than empirically derived and physically ill-understood distance indicators (such as those based upon prompt burst time-profiles and spectra). Second, a more homogeneous set should be constructed by culling subclasses from the larger sample. These subclasses, although now first recognizable by deviant energies, ultimately must be identifiable by properties other than those directly related to energy. We identify a new subclass of GRBs ("f-GRBs") that appear both underluminous by factors of at least 10 and exhibit a rapid fading (fν ∝ t-2) at early times (t ≲ 0.5 day). About 10%-20% of observed long-duration bursts appear to be f-GRBs.

The Speed and Orientation of the Parsec‐Scale Jet in 3C 279

A high degree of relativistic beaming is inferred for the jets of blazars on the basis of several lines of evidence, but the intrinsic speed and angle of the jet to the line of sight for individual sources are difficult to measure. We have calculated inverse Compton Doppler factors for 3C 279 using the collection of VLBI data (including high-resolution space VLBI data at low frequencies) recently published by us (as Wehrle et al. and Piner et al.) and the collection of multiwavelength spectra recently published by Hartman et al. From the Doppler factor and superluminal apparent speed, we then calculate the Lorentz factor and angle to the line of sight of the parsec-scale relativistic jet. We follow the method previously used by Unwin et al. for 3C 345 to model the jet components as homogeneous spheres and the VLBI core as an unresolved inhomogeneous conical jet, using K?nigl's formalism. The conical jet model can be made to match both the observed X-ray emission and the VLBI properties of the core with a suitable choice of Doppler factor, implying that the core makes a significant contribution to the X-ray emission, in contrast to the situation for 3C 345, where the jet components dominated the X-ray emission. The parameters of the K?nigl models indicate that the jet is particle dominated at the radii that produce significant emission (from ~5 to 20 pc from the apex of the jet for most models) and is not in equipartition. At the inner radius of the K?nigl jet the magnetic field is of order 0.1 G and the relativistic-particle number density is of order 10 cm-3. The kinetic energy flux in the jet is of order 1046(1 + k) ergs s-1, where k is the ratio of proton to electron energy, which implies a mass accretion rate of order 0.1(1 + k)/? M? yr-1, where ? is the efficiency of conversion of mass to kinetic energy. When all components are included in the calculation, then on average the core produces about half of the X-rays, with the other half being split between the long-lived component C4 and the brightest inner-jet component. We calculate an average speed and angle to the line of sight for the region of the jet interior to 1 mas of v = 0.992c (? = 8) and ? = 4? and an average speed and angle to the line of sight for C4 (at r ? 3 mas) of v = 0.997c (? = 13) and ? = 2?. These values imply average Doppler factors of ? = 12 for the inner jet and ? = 21 for C4.

Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir

We present a comprehensive sample of all gamma-ray burst (GRB) afterglows with known distances, and we derive their conical opening angles based on observed broadband breaks in their light curves. Within the framework of this conical jet model, we correct for the geometry and we find that the gamma-ray energy release is narrowly clustered around 5 × 10^(50) ergs. We draw three conclusions. First, the central engines of GRBs release energies that are comparable to ordinary supernovae. Second, the broad distribution in fluence and luminosity for GRBs is largely the result of a wide variation of opening angles. Third, only a small fraction of GRBs are visible to a given observer, and the true GRB rate is several hundred times larger than the observed rate.

Infrared synchrotron oscillations in GRS 1915+105

We report simultaneous observations of the black hole candidate X-ray transient GRS 1915+105 in the infrared (IR) at K and in the radio at 2 cm. Oscillations of period 26 min were observed in both wavebands, having (dereddened) peak–peak amplitudes of about 40 mJy and with the IR leading the radio by 7 min, or perhaps by 33 or 59 min. A synchrotron origin for the oscillations continues to seem very likely. We consider a range of problems raised by these observations, and briefly discuss the applicability of expanding-synchrotron source or conical jet models to the oscillations. Comparing simplistic estimates of the ejecta mass to the missing inner disc mass in the model of Belloni et al., we find that a significant fraction of the inner disc may be ejected during the oscillations.

Hollow conical jet models for SS 433 - A paradigm lost?

view Abstract Citations (20) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hollow Conical Jet Models for SS 433: A Paradigm Lost? Kochanek, Christopher S. ; Hawley, John F. Abstract A precessing jet such as that in SS 433 may be approximated as an axisymmetric flow, if the precession time is short by comparison to the propagation time. A series of simulations has been conducted for precessing jets using an axisymmetric finite-difference hydrodynamics code. Examinations are made of hollow cylindrical jets, which lack the complication of a growing interior volume, and conical jets, which model the behavior of a precessing jet propagating on the surface of its precession cone. Publication: The Astrophysical Journal Pub Date: February 1990 DOI: 10.1086/168411 Bibcode: 1990ApJ...350..561K Keywords: Astronomical Models; Computational Astrophysics; Eclipsing Binary Stars; Radio Jets (Astronomy); Bow Waves; Emission Spectra; Finite Difference Theory; Precession; Shock Waves; Supernova Remnants; Astrophysics; GALAXIES: JETS; HYDRODYNAMICS; NEBULAE: INDIVIDUAL ALPHANUMERIC: W50; STARS: INDIVIDUAL ALPHANUMERIC: SS 433 full text sources ADS | data products SIMBAD (2)

X-ray and ultra-violet observations of Markarian 421

We present a physical interpretation of the the dramatic spectral variability observed in the XUV band of the X-ray bright BL Lac type object Markarian 421 (Mrk421). We show that a conical relativistic jet model can adequately explain the data if the upper cut-off in the synchrotron emitting electron population has a variable radial dependence. The physical parameters in the region of the jet responsible for the bulk of the X-ray emission in Mrk421 are derived in the context of such a model.