Relativistic jets from supermassive black holes are among the most powerful and luminous astrophysical systems in Universe. We propose that the open magnetic field lines through the black hole, which drive a strongly magnetized jet, may have their polarity reversing over time scales related to the growth of the magneto-rotational dynamo in the disc, resulting in dissipative structures in the jet characterized by reversing toroidal field polarities, referred to as ``stripes''. Magnetic reconnection between the stripes dissipates the magnetic energy and powers jet acceleration. The striped jet model can explain the jet acceleration, large-scale jet emission, and blazar emission signatures consistently in a unified physical picture. Specifically, we find that the jet accelerates to the bulk Lorentz factor $Γ\gtrsim 10$ within one parsec distance from the central engine. The acceleration slows down but continues at larger distances, with intrinsic acceleration rate $\dotΓ/Γ$ between $0.0005~\rm{yr^{-1}}$ and $0.005~\rm{yr^{-1}}$ at tens of parsecs, which is in very good agreement with recent radio observations. Magnetic reconnection continuously accelerates nonthermal particles over large distances from the central engine, resulting in the core-shift effect and overall flat-to-inverted synchrotron spectrum. The large-scale spectral luminosity peak $ν_{\rm peak}$ is anti-proportional to the location of the peak of the dissipation, which is set by the minimal stripe width $l_{\rm min}$. The blazar zone is approximately at the same location. At this distance, the jet is moderately magnetized, with the comoving magnetic field strength and dissipation power consistent with typical leptonic blazar model parameters.
We have performed a series of numerical experiments aimed at studying the activation of Kerr black holes (BHs) by advection of small scale magnetic fields. Such configurations may potentially give rise to the formation of quasi-striped Blandford-Znajek jets. It can also lead to enhanced dissipation and generation of plasmoids in current sheets formed in the vicinity of the BH horizon, which may constitute a mechanism to power the hard X-ray emission seen in many accreting BH systems (a la lamppost models). Our analysis suggests that formation of quasi-striped jets with significant power may be…
Models invoking magnetic reconnection as the particle acceleration mechanism within relativistic jets often adopt a gradual energy dissipation profile within the jet. However, such a profile has yet to be reproduced in first-principles simulations. Here, we perform a suite of 3D general relativistic magnetohydrodynamic simulations of post-neutron star merger disks with an initially purely toroidal magnetic field. We explore the variations in both the microphysics (e.g., nuclear recombination, neutrino emission) and system parameters (e.g., disk mass). In all our simulations, we find the format…
We study the relationship between jet power and accretion for Fermi and non-Fermi blazars, respectively. We also compare the relevant parameter between them. Our main results are as follows. (i) Fermi and non-Fermi blazars have significant difference in redshift, black hole mass, and broad line luminosity. (ii) Fermi blazars have higher average core-dominance parameter than non-Fermi blazars, which suggests that Fermi blazars have strong beaming effect. (iii) We find significant correlation between broad line emission and jet power for Fermi and non-Fermi blazars, respectively, which suggests …
In this work I review the observational constraints imposed on the energetics and magnetisation of quasar jets, in the context of theoretical expectations. The discussion is focused on issues regarding the jet production efficiency, matter content, and particle acceleration. I show that if the ratio of electron-positron-pairs to protons is of order $15$, as is required to achieve agreement between jet powers computed using blazar spectral fits and those computed using radio-lobe calorimetry, the magnetization of blazar jets in flat-spectrum-radio-quasars (FSRQ) must be significant. This result…
Based on a large Fermi blazar sample, the blazar sequence (synchrotron peak frequency $ν_{\rm peak}$ versus synchrotron peak luminosity $L_{\rm peak}$) is revisited. It is found that there is significant anti-correlation between $ν_{\rm peak}$ and $L_{\rm peak}$ for blazars. However, after being Doppler corrected, the anti-correlation disappears. The jet cavity power ($P_{\rm jet}$) is estimated from extended radio luminosity. So it is free of beaming effect. We find that there are significant anti-correlations between $P_{\rm jet}$ and beam-corrected $ν_{\rm peak}^{'}$ for both blazars and ra…
Luminosities of many powerful blazars are strongly dominated by $γ$-rays which most likely result from Comptonization of radiation produced outside a jet. This observation sets certain constraints on composition and energetics of the jet as well as the surrounding quasar environment. We study the dependence of a Compton dominance on a jet magnetization (the magnetic-to-matter energy flux) and on the location of the 'blazar zone'. Calculations are performed for two geometries of broad-emission-line and hot-dust regions: spherical and planar. The jet magnetization corresponding to the large obse…
By statistically analyzing a large sample which includes blazars of Fermi detection (FBs) and non-Fermi detection (NFBs), we find that there are significant differences between FBs and NFBs for redshift, black hole mass, jet kinetic power from "cavity" power, broad-line luminosity, and ratio of core luminosity to absolute V-band magnitude ($R_{\rm v}$), but not for ratio of radio core to extended flux ($R_{\rm c}$) and Eddington ratio. Compared with NFBs, FBs have larger mean jet power, $R_{\rm c}$ and $R_{\rm v}$ while smaller mean redshift, black hole mass, broad-line luminosity. These resul…
Electrons emitting non-thermal photons in blazars are possibly accelerated by turbulences developed in jets. In this paper, we consider the case so-called hard-sphere scattering as an interaction model between turbulences and electrons, in which the acceleration timescale is independent of the electron energy. We numerically simulate broad-band emission from blazar jets with a one-zone time-dependent code, taking into account the turbulence acceleration. Our model reproduces various blazar spectra with simple assumptions, such as constant particle injection rate, constant diffusion coefficient…
We describe and present initial results from a Fermi cycle 2 program designed to monitor the behavior of the centimeter-band linear polarization and total flux density emitted by gamma-ray-bright blazars during flaring. The goal of the program is to identify changes in the magnetic field structure in the radio jet associated with gamma-ray flaring and ultimately to test whether gamma-ray flaring is associated with the onset of shocks in the radio jet. Light curves illustrating radio band variability patterns are shown for sample program sources.
Hard X-ray observations are crucial to study the non-thermal jet emission from high-redshift, powerful blazars. We observed two bright z>2 flat spectrum radio quasars (FSRQs) in hard X-rays to explore the details of their relativistic jets and their possible variability. S5 0014+81 (at z=3.366) and B0222+185 (at z=2.690) have been observed twice by the Nuclear Spectroscopic Telescope Array (NuSTAR) simultaneously with Swift/XRT, showing different variability behaviours. We found that NuSTAR is instrumental to explore the variability of powerful high-redshift blazars, even when no gamma-ray emi…
The fast TeV variability of the blazars Mrk 501 and PKS 2155--304 implies a compact emitting region that moves with a bulk Lorentz factor of Gamma_{em}~100 toward the observer. The Lorentz factor is clearly in excess of the jet Lorentz factors Gamma_j\simless 10 measured on sub-pc scales in these sources. We propose that the TeV emission originates from compact emitting regions that move relativistically {\it within} a jet of bulk Gamma_j~10. This can be physically realized in a Poynting flux-dominated jet. We show that if a large fraction of the luminosity of the jet is prone to magnetic diss…
In examining a select sample of over 200 blazars of known jet kinetic power (L_kin) and well-characterized SEDs, we found (Meyer et al., 2011) that Intermediate synchrotron-peaking (ISP) blazars may have lower gamma-ray output than high synchrotron-peaking (HSP) blazars of similar L_kin, consistent with our hypothesis that ISP blazars are less-beamed versions of HSP blazars, rather than a distinct population. Further, by using the radio core dominance as a measure of relative beaming, we find that gamma-ray luminosity depends on beaming in a consistent way for blazars ranging over all jet kine…
We fit the (quasi-)simultaneous multi-waveband spectral energy distributions (SEDs) for a sample of low-synchrotron-peaked (LSP) blazars with a one-zone leptonic model. The seed photons that predominantly come from broad line region (BLR) and infrared (IR) molecular torus are considered respectively in external Compton process. We find that the modeling with IR seed photons is systematically better than that with BLR photons based on a $χ^2$ test, which suggest that $γ$-ray emitting region most possibly stay outside the BLR. The minimum electron Lorentz factor, $γ_{\rm min}$, is constrained fr…
Context: Understanding the acceleration mechanism of astrophysical jets has been a cumbersome endeavor from both the theoretical and observational perspective. Although several breakthroughs have been achieved in recent years, on all sides, we are still missing a comprehensive model for the acceleration of astrophysical jets. Aims: In this work we attempt to construct a simple toy model that can account for several observational and theoretical results and allow us to probe different aspects of blazar jets usually inaccessible to observations. Methods: We used the toy model and Lorentz factor …
We compile a sample of spectral energy distribution (SED) of 12 GeV radio galaxies (RGs), including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification as expected in the unification model is found for the derived jet parameters between FR I RGs and BL Lacertae objects (BL Lacs) and between FR II RGs and flat spectrum radio quasars (FSRQs). However, on average FR I RGs have the larger gamma_b (break Lorentz factor of electrons) and lower B (magnetic field strength) than FR II RGs, analogous to the differences between BL …
The impact of the Fermi Gamma-ray Space Telescope on blazar research is reviewed. This includes a brief description of the Fermi Large Area Telescope, a summary of the various classes of extragalactic sources found in the First Large Area Telescope AGN Catalog, and more detailed discussion of the flat spectrum radio quasar 3C454.3 and the BL Lac object PKS 2155-304. Some theoretical studies related to ongoing blazar research with Fermi are mentioned, including implications of gamma-ray observations of radio galaxies on blazar unification scenarios, variability in colliding shells, and whether …
Blazars have been regarded as one of the most powerful sources of the highest energy cosmic rays and also their byproducts, neutrinos. Provided that a magnetized filamentary system is established in a blazar jet as well, we could apply the mechanism of multi-stage diffusive shock acceleration to a feasible TeV emitter, Mrk 501 to evaluate the achievable maximum energy of protons. Taking conceivable energy restriction into account systematically, it seems adequate to say that EeV-protons are produced at this site by our present model. We also estimate neutrino fluxes generated by these accelera…
Polarization offers a unique view in the physical processes of astrophysical jets. We report on optical circular polarization observations of two famous blazars, namely 3C 279 and PKS 1510-089, at high linearly polarized states. This is the first time PKS 1510-089 is observed in optical circular polarization. While only upper limits can be extracted from our observing campaign, the non-detection of optical circular polarization allows us to provide meaningful constraints on their magnetic field strength and jet composition. We find that high-energy emission models requiring high magnetic field…
Blazars exhibit flares across the entire electromagnetic spectrum. Many $γ$-ray flares are highly correlated with flares detected at longer wavelengths; however, a small subset appears to occur in isolation, with little or no correlated variability at longer wavelengths. These "orphan" $γ$-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. Macdonald et al. have developed the Ring of Fire model to explain the origin of orphan $γ$-ray flares from within blazar jets. In this model, electrons contained within a blob of plasma mov…
The multi-wavelength spectral and temporal variability observed in blazars set tight constraints on current theoretical emission models. Here, we investigate the relativistic magnetic reconnection process as a source of blazar emission in which quasi-spherical plasmoids, containing relativistic particles and magnetic fields, are associated with the emission sites in blazar jets. By coupling recent two-dimensional particle-in-cell simulations of relativistic reconnection with a time-dependent radiative transfer code, we compute the non-thermal emission from a chain of plasmoids formed during a …
Black hole - accretion disc systems are the central engines of relativistic jets from stellar to galactic scales. We numerically quantify the unsteady outgoing Poynting flux through the horizon of a rapidly spinning black hole endowed with a rotating accretion disc. The disc supports small-scale, concentric, flux tubes with zero net magnetic flux. Our General Relativistic force-free electrodynamics simulations follow the accretion onto the black hole over several hundred dynamical timescales in 3D. For the case of counter-rotating accretion discs, the average process efficiency reaches up to $…
We report on our observations of the parsec-scale radio jet structures of five blazars that have been detected by ground-based TeV gamma-ray telescopes. These five blazars all belong to the class of high-frequency peaked BL Lac objects (HBLs), which are the most common blazar type detected at the TeV energy range. Because of their relative faintness in the radio, these HBLs are not well represented in other radio blazar surveys. Our observations consist of five epochs of Very Long Baseline Array (VLBA) imaging from 2006 to 2009, of each of the five blazars 1ES 1101-232, Markarian 180, 1ES 1218…
Blazars are a subclass of radio-loud active galactic nuclei (AGNs), where the jet is aligned close to the line of sight. Blazars emission is dominated by non-thermal processes, where Doppler boosted radiation originates from a relativistic population of charged particles within the jet. From radio to TeV energies, blazars are highly variable on timescales from minutes to several months. There are several mechanisms proposed to explain variability, including changes in the viewing angle of the jet, propagating along the rotation axis of the accretion disc. The misalignment of a supermassive bla…
Black holes, anywhere in the stellar-mass to supermassive range, are often associated with relativistic jets. Models suggest that jet production may be a universal process common in all black hole systems regardless of their mass. Although in many cases observations support such hypotheses for microquasars and Seyfert galaxies, little is known on whether boosted blazar jets also comply with such universal scaling laws. We use uniquely rich multiwavelength radio light curves from the F-GAMMA program and the most accurate Doppler factors available to date to probe blazar jets in their emission r…
The innermost parts of powerful jets in active galactic nuclei are surrounded by dense, high-velocity clouds from the broad-line region, which may penetrate into the jet and lead to the formation of a strong shock. Such jet-cloud interactions are expected to have measurable effects on the $γ$-ray emission from blazars. We characterise the dynamics of a typical cloud-jet interaction scenario, and the evolution of its radiative output in the 0.1-30~GeV energy range, to assess to what extent these interactions can contribute to the $γ$-ray emission in blazars. We use semi-analytical descriptions …
Blazars are usually classified following their synchrotron peak frequency ($νF(ν)$ scale) as high, intermediate, low frequency peaked BL Lacs (HBLs, IBLs, LBLs), and flat spectrum radio quasars (FSRQs), or, according to their radio morphology at large scale, FR~I or FR~II. However, the diversity of blazars is such that these classes seem insufficient to chart the specific properties of each source. We propose to classify a wide sample of blazars following the kinematic features of their radio jets seen in very long baseline interferometry (VLBI). For this purpose we use public data from the MO…
Low ($\lesssim 1\%$) levels of circular polarization (CP) detected at radio frequencies in the relativistic jets of some blazars can provide insight into the underlying nature of the jet plasma. CP can be produced through linear birefringence, in which initially linearly polarized emission produced in one region of the jet is altered by Faraday rotation as it propagates through other regions of the jet with varying magnetic field orientation. Marscher has begun a study of jets with such magnetic geometries using the Turbulent Extreme Multi-Zone (TEMZ) model, in which turbulent plasma crossing …
Various quasi-periods for the long-term variability of the radio emission, optical emission, and structural position angle of the inner part of the parsec-scale jet in the blazar 0716+714 have been detected. The relationships between these quasi-periods are interpreted assuming that the variability arises due to a helical structure of the jet, which is preserved from regions near the jet base to at least 1 milliarcsecond from the core observed in radio interferometric observations. The radiating jet components should display radial motions with Lorentz factors of $\approx3$, and decelerate wit…
Many theories beyond the Standard Model of particle physics predict the existence of axionlike particles (ALPs) that mix with photons in the presence of a magnetic field. One prominent indirect method of searching for ALPs is to look for irregularities in blazar gamma-ray spectra caused by ALP-photon mixing in astrophysical magnetic fields. This requires the modelling of magnetic fields between Earth and the blazar. So far, only very simple models for the magnetic field in the blazar jet have been used. Here we investigate the effects of more complicated jet magnetic field configurations on th…
We have not identified for sure what is the mechanism launching, accelerating and collimating relativistic jets. The two most likely possibilities are the gravitational energy of the accreting matter or the rotational energy of a spinning black hole. Even the evaluation of the jet power is not trivial, since the radiation from the jet is enhanced by relativistic beaming, and there are fundamental uncertainties concerning the matter content of the jet (electron--proton or electron--positron plasma). However, in recent years, there have been crucial advances mainly driven by the richness of data…
Detection of blazar pc scale counter-jets is difficult, but it can provide invaluable insight into the relativistic effects, radiative processes and the complex mechanisms of jet production, collimation and accelation in blazars. We build on recent populations models (optimized using the MOJAVE apparent velocity and redshift distributions) in order to derive the distribution of jet-to-counter-jet ratios and the flux densities of the counter-jet at different frequencies, in an effort to set minimum sensitivity limits required for existing and future telescope arrays in order to detect these elu…
The internal-shocks scenario in relativistic jets has been used to explain the variability of blazars' outflow emission. Recent simulations have shown that the magnetic field alters the dynamics of these shocks producing a whole zoo of spectral energy density patterns. However, the role played by magnetization in such high-energy emission is still not entirely understood. With the aid of \emph{Fermi}'s second LAT AGN catalog, a comparison with observations in the $γ$-ray band was performed, in order to identify the effects of the magnetic field.
X-ray polarimetry promises us an unprecedented look at the structure of magnetic fields and on the processes at the base of acceleration of particles up to ultrarelativistic energies in relativistic jets. Crucial pieces of information are expected from observations of blazars (that are characterized by the presence of a jet pointing close to the Earth), in particular of the subclass defined by a synchrotron emission extending to the X-ray band (so-called high synchrotron peak blazars, HSP). In this review, I give an account of some of the models and numerical simulations developed to predict t…
Here we report on the total-intensity 610 MHz GMRT observations of the peculiar hybrid blazar SBS B1646+499, which merges the properties of BL Lacertae objects and flat-spectrum radio quasars. The complex radio structure of SBS B1646+499, emerging from the archival radio data and our new GMRT observations, consists of the Mpc-scale, elongated halo, the unilateral kpc-scale jet, and the nuclear jet extending up to 20pc from the compact core. The giant halo is characterized by a steep radio spectrum, indicative of the advanced ageing of the electron population within the lobes. For the large-sca…
We have analyzed a large sample of clean blazars detected by Fermi Large Area Telescope (LAT). Using literature and calculation, we obtained intrinsic $γ$-ray luminosity excluding beaming effect, black hole mass, broad-line luminosity (used as a proxy for disk luminosity), jet kinetic power from "cavity" power and bulk Lorentz factor for parsec-scale radio emission, and studied the distributions of these parameters and relations between them. Our main results are as follows. (i) After excluding beaming effect and redshift effect, intrinsic $γ$-ray luminosity with broad line luminosity, black h…
Different Jet Dissipation Mechanisms Underlying the Variability in Blazars
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；Tianfu Cosmic Ray Research Center（天府宇宙线研究中心）
Since the mid-1980s the shock-in-jet model has been the preferred paradigm to explain radio-band flaring in blazar jets. We describe our radiative transfer model incorporating relativistically-propagating shocks, and illustrate how the 4.8, 8, and 14.5 GHz linear polarization and total flux density data from the University of Michigan monitoring program, in combination with the model, constrain jet flow conditions and shock attributes. Results from strong Fermi-era flares in 4 blazars with widely-ranging properties are presented. Additionally, to investigate jet evolution on decadal time scale…
Blazars in elliptical hosts have a population of red giants surrounding their jet. These stars can carry large wind-blown bubbles into the jets, leading to gamma-ray emission through bubble-jet interactions. We study the interaction dynamics and the gamma-ray emission produced when the bubbles formed by red giant winds penetrate the jet of a blazar in an elliptical galaxy. First, we characterized the masses and penetration rates of the red giant wind bubbles that enter the jet. Then, the dynamical evolution of these bubbles under the jet impact was analysed analytically and numerically, and th…
Reinhard Schlickeiser has made groundbreaking contributions to various aspects of blazar physics, including diffusive shock acceleration, the theory of synchrotron radiation, the production of gamma-rays through Compton scattering in various astrophysical sources, etc. This paper, describing the development of a self-consistent shock-in-jet model for blazars with a synchrotron mirror feature, is therefore an appropriate contribution to a Special Issue in honor of Reinhard Schlickeiser's 70th birthday. The model is based on our previous development of a self-consistent shock-in-jet model with r…
We report on Gemini, NuSTAR and 8-year Fermi observations of the most distant blazar QSO~J0906$+$6930 ($z=5.48$). We construct a broadband spectral energy distribution (SED) and model the SED using a synchro-Compton model. The measurements find a $\sim 4 \times 10^9 M_\odot$ mass for the black hole and a spectral break at $\sim$4 keV in the combined fit of the new NuSTAR and archival Chandra data. The SED fitting constrains the bulk Doppler factor $δ$ of the jet to $9^{+2.5}_{-3}$ for QSO~J0906$+$6930. Similar, but weaker $δ$ constraints are derived from SED modeling of the three other claimed…
We present the results of studying the accretion disk vs jet power for a large fraction of all the blazars detected by the Fermi Gamma-Ray Space Telescope. The disk power is inferred from the emission line luminosities obtained from published results. As indicators of jet power, we use low frequency radio luminosity from the extended jet, maximum speed of radio knots observed in the VLBA monitoring of the pc-scale jets, kinetic energy of electrons in the jet deduced from the best-fit theoretical models of their spectral energy distribution, and gamma-ray luminosity with and without beaming cor…
There is an increasing number of observational evidence that very high energy gamma-rays in radio-loud active galactic nuclei are produced in the direct vicinity of a supermassive black hole (SMBH), close to the base of a relativistic jet. In the case of some blazars, the angle between the jet axis and the observer's line of sight is smaller than the angular extent of the jet. Gamma-rays that are produced close to SMBH therefore have to propagate in the nonthermal radiation of the extended jet before reaching the observer. This gamma-ray emission can be strongly absorbed in the extended jet ra…
Blazars, a class of active galaxies whose jets are relativistic and collimated flows of plasma directed along the line of sight and are prone to a slew of magneto-hydrodynamic (MHD) instabilities. We aim to study the interplay of radiation and particle acceleration processes in regulating the multi-band emission and variability signatures from blazars. In particular, the goal is to decipher the impact of shocks arising due to MHD instabilities in driving the longterm variable emission signatures from blazars. In this regard, we have performed RMHD simulations of a representative section of bla…
The curved shape of the kiloparsec-scale jet of the blazar OJ 287 is analyzed in the framework of the precession of the central engine, on the existence on which a large number of studies over the past decades are based. The data necessary for the analysis of the kiloparsec-scale jet velocity and angle with the line of sight are obtained based on two competing assumptions about the X-ray emission mechanism of the OJ 287 jet. Namely, there were both the inverse Compton scattering of the microwave background under the assumption of relativistic kiloparsec-scale jet and the inverse Compton scatte…
In this paper we develop the extended jet model of Potter & Cotter to model the simultaneous multi-wavelength spectra of six Compton-dominant blazars. We include an accelerating parabolic base transitioning to a slowly decelerating conical jet with a geometry set by observations of M87 and consistent with simulations and theory. We investigate several jet models and find that the optically thick to thin synchrotron break in the radio spectrum requires the jet to first come into equipartition at large distances along the jet (10^5 Schwarzschild radii), consistent with the observed transition fr…
We present our latest results on the connection between accretion rate and relativistic jet power in AGN, by using a large sample which includes mostly blazars, but contains also some radio--galaxies. The jet power can be traced by $γ$--ray luminosity in the case of blazars, and radio luminosity for both classes. The accretion disc luminosity is instead traced by the broad emission lines. Among blazars, we find a correlation between broad line emission and the $γ$--ray or radio luminosities, suggesting a direct tight connection between jet power and accretion rate. We confirm that the observat…
As part of a program to identify the physical conditions in the jets of gamma-ray-flaring blazars detected by Fermi, including the role of shocks in the production of high-energy flaring, we obtained 4 years of 3-frequency, centimeter-band total flux density and linear polarization monitoring observations of the radio-bright blazar S5 0716+714 with the University of Michigan 26-m paraboloid. Light curves constructed from these data exhibit a series of rapid, high-amplitude, centimeter-band total flux density outbursts, and changes in the linear polarization consistent with the passage of shock…
We investigate the location of the radio jet bases ("radio cores") of blazars in radio images, and their stationarity by means of dense very long baseline interferometry (VLBI) observations. In order to measure the position of a radio core, we conducted 12 epoch astrometric observation of the blazar Markarian 421 with the VLBI Exploration of Radio Astrometry at 22 GHz immediately after a large X-ray flare, which occurred in the middle of 2011 September. For the first time, we find that the radio core is not stationary but rather changes its location toward 0.5 mas downstream. This angular scal…
Blazars show variability on timescales ranging from minutes to years, the former being comparable to and in some cases even shorter than the light-crossing time of the central black hole. The observed gamma-ray lightcurves can be described by a power-law power density spectrum (PDS), with a similar index for both BL Lacs and flat-spectrum radio quasars. We show that this variability can be produced by turbulence in relativistic jets launched by magnetically arrested accretion flows (MADs). We perform radiative transport calculations on the turbulent, highly-magnetized jet launching region of a…
Mildly-relativistic shocks that are embedded in colliding magnetohydrodynamic flows are prime sites for relativistic particle acceleration and production of strongly variable, polarized multi-wavelength emission from relativistic jet sources such as blazars and gamma-ray bursts. The principal energization mechanisms at these shocks are diffusive shock acceleration and shock drift acceleration. In recent work, we had self-consistently coupled shock acceleration and radiation transfer simulations in blazar jets in a basic one-zone scenario. These one-zone models revealed that the observed spectr…
The jet composition and energy dissipation mechanism of Gamma-ray bursts (GRBs) and Blazars are fundamental questions which remain not fully understood. One plausible model is to interpret the $γ$-ray emission of GRBs and optical emission of blazars as synchrotron radiation of electrons accelerated from the collision-induced magnetic dissipation regions in Poynting-flux-dominated jets. The polarization observation is an important and independent information to test this model. Based on our recent 3D relativistic MHD simulations of collision-induced magnetic dissipation of magnetically dominate…
High energy emission from blazars is thought to arise in a relativistic jet launched by a supermassive black hole. The emission site must be far from the hole and the jet relativistic, in order to avoid absorption of the photons. In extreme cases, rapid variability of the emission suggests that structures of length-scale smaller than the gravitational radius of the central black hole are imprinted on the jet as it is launched, and modulate the radiation released after it has been accelerated to high Lorentz factor. We propose a mechanism which can account for the acceleration of the jet, and f…
