Possible γ-ray emission of radio intermediate AGN Ⅲ Zw 2 and its implication on the evolution of jets in AGNs

AGNs with hard γ-ray emission identified so far are radio-loud. Ⅲ Zw 2 is a radio intermediate AGN with a relativistic jet. We study its spectral energy distribution （SED） and find that the broad band emissions are dominated by the nonthermal emissions from the jet. We model its SED through a synchrotron ＋ inverse Compton （IC） model. The results show that the IC component of Ⅲ Zw 2 peaks at a few MeV, and the flux density drops rapidly at higher energy with photon index F 3.3 above 0.1 GeV. The predicted flux is slightly over the sensitivity of Fermi/LAT, but it was not included in the first Fermi/LAT AGN catalog. The reason for this may be： 1） that the IC peak is low and the spectrum is very steep above 0.1 GeV, 2） that Ⅲ Zw 2 is in the low state during the period of the Fermi/LAT operation. We also find that Ⅲ Zw 2 follows similar jet processes as those in γ-ray AGNs, e.g., the relation between jet power and radiation power, which is called the blazar sequence. We suggest that Ⅲ Zw 2 may be a young source at an earlier stage of jet activity.

Launching jets from accretion belts

We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications on a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.

Magnetic reconnection acceleration of astrophysical jets for different jet geometries

The acceleration mechanisms of relativistic jets are of great importance for understanding various astrophysical phenomena such as gamma-ray bursts, active galactic nuclei and microquasars. One of the most popular scenarios is that the jets are initially Poynting-flux dominated and succumb to magnetohydrodynamic instability leading to magnetic reconnections. We suggest that the reconnection timescale and efficiency could strongly depend on the geometry of the jet, which determines the length scale on which the orientations of the field lines change. In contrast to a usually- assumed conical jet, the acceleration of a collimated jet can be found to be more rapid and efficient （i.e. a much more highly saturated Lorentz factor can be reached） while the jets with lateral expansion show the opposite behavior. The shape of the jet could be formed due to the lateral squeezing on the jet by the stellar envelope of a collapsing massive star or the interaction of the jet with stellar winds.

Detection of Gamma-Rays from the Protostellar Jet in the HH 80–81 System

Considering that the existence of relativistic particles in the protostellar jet has been confirmed by the detection of linearly polarized radio emission from the HH 80–81 jet,we search for gamma-rays from the HH 80–81 system using ten-year Fermi-LAT observations.A significant point-likeγ-ray excess is found in the direction of the HH80–81 system with the Test-Statistic value>100,which is likely produced in the HH 80–81 jet.Theγ-ray spectrum extends only to 1 Ge V with a photon index of 3.5.No significant variability is found in the gamma-ray emission.It is discussed that the properties of HH 80–81 jet suffice for producing the observedγ-rays.

Dynamics and collisions of episodic jets from black holes and accretion disk systems

In many astrophysical black hole systems, episodic jets of plasma blobs have been observed, which are much faster and more powerful than continuous jets. A magnetohydrodynamical model was proposed by Yuan et al. to study the formation of episodic jets in Sgr A＊. By taking Sgr A＊ and a stellar mass black hole as examples, we modify the model of Yuan et al. by including the effects of relativity, and further study the relativistic motion and expansion of episodic jets of plasma blobs. Then we study the collision between two consecutive ejections in the modified model, and calculate the magnetic energy released in the collision. Our results show two consecutive blobs can collide with each other, and the released magnetic energy is more than 1050 erg, which supports the idea that a gamma-ray burst is powered by the collision of episodic jets, as suggested by Yuan ＆ Zhang.

Lsyn-Esyn,p-δrelation in active galactic nucleus jets and implication for the physical origin of the Lp-Ep,z-Γ_0 relation of gamma-ray bursts

High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s)follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ0)of GRBs.It is shown that the AGN sample does not agree with the Lp-Ep,z-Γ0 relation of GRBs.In addition,we obtain a tight relation of Lsyn∝Е0.45±0.15δ3.50±0.25 syn,p for FSRQs and NLS1 galaxies,where Lsyn is the luminosity at peak photon energy Esyn,p of the synchrotron radiations.This relation is different from the Lp-Ep,z-Γ0 relation of GRB s.The dependence of Lsyn toδis consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue thatΓ0 may be a representative of the kinetic power of the radiating region and the tight Lp-Ep,z-Γ0 relation is shaped by the radiation physics and the jet power together.

AGN Singularities and Jets Modelled with the Superstar Scenario

In this paper we present solutions with the superstar scenario for the problems of singularity and the relativistic jet in AGN (Active Galactic Nuclei) based on supermassive black hole with singularity. The five-zone structure of superstar from inside to outside consists of the Singularity-Free Superstar Core (SC), the short-range repulsive super force field (SFF) near the event horizon, the superstar lepton sphere (SLS) containing infalling leptons (electron-positron pairs), the superstar ergosphere (SE), and the superstar accretion disk (SAD). As in the Meissner effect in superconductor, the short-range SFF repulses leptons in the SLS preventing singularity, while infalling leptons from the SAD and the SE continue to enter the SLS through the strong gravity of the SC. When the density at the bottom of the SLS reaches the critical density, leptons fall into the SC with the corresponding size increase of the SC to prevent singularity. Without further infalling leptons, the short-range repulsive force from the SFF disintegrates the SLS into the SLS plasma fragments (electron-positron pair plasma), detaching from the SC. Some SLS plasma fragments in the SAD generate the broad relativistic SAD jet, and some SLS plasma fragments in the SE generate the coincident narrow relativistic SE jet. In this two-jet model (the origin of the spine-sheath jet structure), protected by the SAD jet, the fast and narrow SE jet inside the slow and broad SAD jet generates the VHE (very high energy ≥ 100 GeV) Synchrotron Self Compton (SSC) gamma-ray emission without the attenuation by the photons in the BLR (broad line region) of flat spectrum radio quasar (FSRQ). In conclusion, AGN based on supermassive superstar provide the solutions for singularity, VHE gamma-ray emissions in FSRQs and FR1 type radio galaxies, AGN jet structure, and AGN jet type.

Bending of Jets in the QSO NRAO 530

We present radio images of NRAO 530 on scales ranging from pc to kpc. The observations include the EVN at 5 GHz, the VLBA at 1.6, 8.6 and 15 GHz, the MERLIN at 1.6 and 5 GHz, and the VLA at 5, 8.4, 15, 22, and 43 GHz. The VLBI images show a core-jet structure with an oscillating trajectory on a scale of about 30 mas north of the strongest compact component （core）. Superluminal motions are detected in five of the jet components with apparent velocities in the range of 13.6 to 25.2c. A new component is detected at 15 GHz with the VLBA observations, which appears to be associated with the outburst in 2002. Significant polarized emission is detected around the core with the VLBA observations at 15 GHz. Rapid variations of the polarization intensity and angle are found between the epochs in 2002 and 2004. On the kpc-scale, a distant component （labelled as WL） located 11 arcsec west （PA=-86°） of the core is detected beyond the core-jet structure which extended to several hundreds of mas in the north-west direction （-50°）. A significant emission between the core-jet structure and the WL is revealed. A clump of diffuse emission （labelled EL, 12 arcsec long） at PA 70° to the core, is also detected in the VLA observations, suggesting the presence of double lobes in the source. The core component shows a fiat spectrum, while the distant components WL and EL have steep spectra. The steep spectra of the distant components and the detection of the arched emission suggest that the distant components are lobes or hot-spots powered by the core of NRAO 530. The morphologies from pc- to kpcscales and the bending of jets are investigated. The observed radio morphology from pc to kcp appears to favor the model in which precession or wobbling of the nuclear disk drives the helical motion of the radio plasma and produces the S-shaped structure on kpc scale.

Comparisons of Jet Properties between GeV Radio Galaxies and Blazars

We compile a sample of spectral energy distributions （SEDs） 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 a larger ＇Tb （break Lorentz factor of electrons） and lower B （magnetic field strength） than FR II RGs, analogous to the differences be- tween BL Lacs and FSRQs. The derived Doppler factors （~） of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent pop- ulations of blazars with smaller tS. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carded by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the ＂sequence＂ behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.

Cylindrical Jet - Wind Interaction Model of Gamma-Ray Burst Afterglows

Observations on relativistic jets in radio galaxies, active galactic nuclei, and 'microquasars' revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evolution of cylindrical jets in gamma-ray bursts. We discuss afterglows from cylindrical jets in a wind environment. Numerical results as well as analytic solutions in some special cases are presented. Our light curves are steeper compared to those in the homogeneous interstellar medium case, carefully considered by Cheng, Huang & Lu. We conclude that some afterglows, used to be interpreted as isotropic fireballs in a wind environment, can be fitted as well by cylindrical jets interacting with a wind.

On the Jet Structures of GRB 050820A and GRB 070125

We present the broadband numerical modeling of afterglows for two remarkably bright long gamma-ray bursts(GRBs),GRB 050820 A and GRB 070125,with a wide range of observations from the radio band to the X-ray band.In our work,we fit light curves and constrain physical parameters using a standard forward shock model from the afterglowpy Python package,considering different jet structures and the jet lateral expansion.For GRB 050820 A,the constrained jet is close to a top-hat jet with an extremely small half opening angle of about 0.015 rad,and the circumburst matter density is as small as 10^(-7)cm^(-3),which suggests that this peculiar long GRB might originate from metal-poor stars with low mass-loss rates.To explain the late time optical light curves of GRB 070125,the effects of the lateral expansion and the participation factor of electrons that are accelerated by the shock have to be taken into account.The constrained results for GRB 070125 show that the jet is also close to a top-hat jet with a half opening angle of about 0.1 rad,the viewing angle is about 0.05 rad,the circumburst density is about 10 cm^(-3),and the participation factor is about 0.1.The jet energy of the two bursts is required to be~1051–1052 erg,which can be produced by a millisecond magnetar or a hyper-accreting black hole.

The afterglow emission from a stratified jet in GRB 170817A

The afterglow of GRB 170817 A has been detected for more than three years,but the origin of the multi-band afterglow light curves remains under debate.A classical top-hat jet model is faced with difficulties in producing a shallow rise of the afterglow light curves as observed(E_(v) ∝ T^(0.8)).Here we reconsider the model of stratified ejecta with an energy profile of E(> Γβ)=E_0(Γβ)^(-k) as the origin of the afterglow light curves of the burst,where Γ and β are the Lorentz factor and speed of the ejecta,respectively.k is the power-law slope of the energy profile.We consider that the ejecta are collimated into jets.Two kinds of jet evolutions are investigated,including a lateral-spreading jet and a non-lateral-spreading jet.We fit the multi-band afterglow light curves,including the X-ray data at one thousand days post-burst,and find that both the models of the spreading and non-spreading jets can fit the light curves well,but the observed angular size of the source and the apparent velocity of the flux centroid for the spreading jet model are beyond the observation limits,while the non-spreading jet model meets the observation limits.Some of the best-fit parameters for the non-spreading jet model,such as the number density of the circumburst medium~10^(-2) cm^(-3) and the total jet kinetic energy E ~ 4.8 × 10^(51) erg,also appear plausible.The best-fit slope of the jet energy profile is k ~7.1.Our results suggest that the afterglow of GRB 170817 A may arise from the stratified jet and that the lateral spreading of the jet is not significant.

GRB 220408B:A Three-episode Burst from a Precessing Jet

Jet precession has previously been proposed to explain the apparently repeating features in the light curves of a few gamma-ray bursts(GRBs).In this paper,we further apply the precession model to a bright GRB 220408B by examining both its temporal and spectral consistency with the predictions of the model.As one of the recently confirmed GRBs observed by our GRID CubeSat mission,GRB 220408B is noteworthy as it exhibits three apparently similar emission episodes.Furthermore,the similarities are reinforced by their strong temporal correlations and similar features in terms of spectral evolution and spectral lags.Our analysis demonstrates that these features can be well explained by the modulated emission of a Fast-Rise-Exponential-Decay(FRED)shape light curve intrinsically produced by a precessing jet with a precession period of 18.4_(-0.2)~(+0.2)s,a nutation period of11.1_(-0.2)~(+0.2)s and viewed off-axis.This study provides a straightforward explanation for the complex yet similar multiepisode GRB light curves.

A modified stratified model for the 3C 273 jet

We present a modified stratified jet model to interpret the observed spectral energy distributions of knots in the 3C 273 jet. Based on the hypothesis of the single index of the particle energy spectrum at injection and identical emission processes among all the knots, the observed difference of spectral shape among different 3C 273 knots can be understood as a manifestation of the deviation of the equivalent Doppler factor of stratified emission regions in an individual knot from a characteristic one. The summed spectral energy distributions of all ten knots in the 3C 273 jet can be well fitted by two components; a low-energy component （radio to optical） dominated by synchrotron radiation and a high- energy component （UV, X-ray and γ-ray） dominated by inverse Compton scattering of the cosmic microwave background. This gives a consistent spectral index of α = 0.88 （Sv ∝ v^-α） and a characteristic Doppler factor of 7.4. Assuming the average of the summed spectrum as the characteristic spectrum of each knot in the 3C 273 jet, we further get a distribution of Doppler factors. We discuss the possible implications of these results for the physical properties in the 3C 273 jet. Future GeV observations with GLAST could separate the 7-ray emission of 3C 273 from the large scale jet and the small scale jet （i.e. the core） through measuring the GeV spectrum.

Kinematics of the high-excitation HH 890 jet in the Rosette Nebula

Photoionized jets immersed in HII regions display special properties, which made them a distinctive category of Herbig-Haro （HH） flows. Detailed studies of such jet systems became one of the key issues in our understanding of jet production and evolution. HH 890, initially called the Rosette HH2 jet, is the second photoionized jet discovered in the spectacular HII region of the Rosette Nebula. Contrary to conventional impressions of a jet, its discrete components are found to be unexpectedly broad and spatially detached from the proposed energy source. The jet displays additional unusual features which point to the disputable nature of the system. Here, we investigate the kinematics of the jet through high-quality echelle spectrograms. It is distinctively resolved into a fast component with a mean approaching velocity of-39 km s^-1 with respect to the systemic rest frame and a slow component with radial velocity centered at -9 km s^-1. The slow component indicates an apparently larger dispersion in radial velocity in various emission lines and is likely dissolving at roughly the speed of sound, which favors a photoevaporated origin. The [SII] doublet ratios indicate an electron density of -1.1×10^3 cm^-3 in the collimated jet and ,-9×10^2 cm^-3 in the HII region. This, along with the diffuse appearance of the extensive part of the jet, leads to a dissipation of the jet in the fully ionized medium of Rosette. In addition, time series of photometric observations provide evidence for remarkable light variations of the energy source. Its amplitudes of variation amount to 〉 1 mag in both R and I, which is commensurate with the young evolutionary status of the source as indicated by a red, late type optical spectrum.

A two-component jet model based on the Blandford-Znajek and Blandford-Payne processes

We propose a two-component jet model consistent with the observations of several gamma ray bursts （GRBs） and active galactic nuclei （AGNs）. The jet consists of inner and outer components, which are supposed to be driven by the Blandford- Znajek （BZ） and Blandford-Payne （BP） processes, respectively. The baryons in the BP jet are accelerated centrifugally via the magnetic field anchored in the accretion disk. The BZ jet is assumed to be entrained in a fraction of accreting matter leaving the inner edge of the accretion disk, and the baryons are accelerated in the conversion from electromagnetic energy to kinetic energy. By fitting the Lorentz factors of some GRBs （GRB 030329, GRB 051221A and GRB 080413B） and AGNs （Cen A, Mkn 501 and Mkn 421） with this model, we constrain the physical parameters related to the accretion and outflow of these two kinds of objects. We conclude that the spine/sheath structure of the jet from these sources can be interpreted naturally by the BZ and BP processes.

Jet-dominated quiescent state in black hole X-ray binaries: the cases of A0620–00 and XTE J1118+480

The radiative mechanism of black hole X-ray transients （BHXTs） in their quiescent states （defined as the 2-10 keV X-ray luminosity ≤ 10^34 erg s-1） remains unclear. In this work, we investigate the quasi-simultaneous quiescent state spectrum （including radio, infrared, optical, ultraviolet and X-ray） of two BHXTs, A0620-00 and XTE J1118＋480. We find that these two sources can be well described by a coupled accretion - jet model. More specifically, most of the emission （radio up to infrared, and the X-ray waveband） comes from the collimated relativistic jet. Emission from hot accretion flow is totally insignificant, and it can only be observed in mid-infrared （the synchrotron peak）. Emission from the outer cold disk is only evident in the UV band. These results are consistent with our previous investigation on the quiescent state of V404 Cyg and confirm that the quiescent state is jet-dominated.

Inner jet kinematics and the viewing angle towards the γ-ray narrow-line Seyfert 1 galaxy 1H 0323＋342

Near-Eddington accretion rates onto low-mass black holes are thought to be a prime driver of the multi-wavelength properties of the narrow-line Seyfert 1 （NLS1） population of active galactic nuclei （AGNs）. Orientation effects have repeatedly been considered as another important factor involved, but detailed studies have been hampered by the lack of measured viewing angles towards this type of AGN. Here we present multi-epoch, 15 GHz VLBA images （MOJAVE program） of the radio-loud and Fermi/LAT- detected NLS 1 galaxy 1H 0323＋342. These are combined with single-dish, multi-frequency radio monitoring of the source＇s variability, obtained with the Effelsberg 100-m and IRAM 30-m telescopes, in the course of the F-GAMMA program. The VLBA images reveal six components with apparent speeds of 1 - 7 c, and one quasi-stationary feature. Combining the obtained apparent jet speed （βapp） and variability Doppler factor （Dvar） estimates together with other methods, we constrain the viewing angle 0 towards 1H 0323＋342 to 0 ≤ 4°-13°. Using literature values of βapp and Dvar, we also deduce a viewing angle of 〈8°-9° towards another radio- and γ-ray-loud NLS1, namely SBS 0846＋513.

Diffuse emission of TeV neutrinos and gamma-rays from young pulsars by photomeson interaction in the Galaxy

It is generally believed that young, rapidly rotating pulsars are important sites of particle acceleration, in which protons can be accelerated to relativistic energy above the polar cap region if the magnetic moment is antiparallel to the spin axis （μ·Ω 〈 0）. To obtain diffuse neutrinos and gamma-rays at TeV that originate in our Galaxy, we use the Monte Carlo method to generate a sample of young pulsars with ages less than 106 yr in our galaxy; the neutrinos and high-energy gamma-rays can be produced through a photomeson process with the interaction of energetic protons and soft X-ray photons （p ＋γ→△＋→n＋π＋/p＋π0） for a single pulsar, and these X-ray photons come from the surface of the neutron star. The results suggest that the flux of diffuse neutrinos at TeV energies is lower than the background flux, indicating they are difficult to detect using current neutrino telescopes.

GRB jet beaming angle statistics

Existing theory and models suggest that a Type I （merger） GRB should have a larger jet beaming angle than a Type II （collapsar） GRB, but so far no statistical evidence is available to support this suggestion. In this paper, we obtain a sample of 37 beaming angles and calculate the probability that this is true. A correction is also devised to account for the scarcity of Type I GRBs in our sample. The probability is calculated to be 83% without the correction and 71% with it.