arXiv subjects

Zhen-Jie Wang

Publications and source records attributed to Zhen-Jie Wang.

7 recordsLinked to original sources

arXiv2026

A Model for Magnetic Reconnection as the Origin of TeV Outbursts from NGC 1275

NGC 1275 showed two TeV $γ$-ray outbursts between November 2022 and January 2023, as detected by the Large High Altitude Air Shower Observatory (LHAASO). The source was also active in the X-ray and GeV bands during the TeV outburst period. Very-long-baseline radio observations reported a sudden acceleration and deflection of a jet knot in late 2022, before the main TeV activity. Motivated by this sequence, we examine whether magnetic reconnection triggered by the interaction between the jet and the ambient medium can explain the TeV flares. In this picture, reconnection produces many plasmoids, and a large ``monster'' plasmoid becomes the main flare region. We model the low-state emission with a multi-zone stochastic-dissipation component and add a compact reconnection-powered region for the flaring state. We then compare leptonic and hadronic interpretations. The leptonic model explains the enhanced X-ray emission as electron synchrotron radiation and the TeV emission mainly as inverse-Compton radiation. A pure proton--proton model can also produce TeV photons if dense target gas is present, but it requires a compact cloud with a density above the values directly inferred from free--free absorption and a large proton power. These requirements are demanding, but they do not by themselves exclude the hadronic interpretation, because the gas may be compressed by the jet or may contain denser cloud cores. Our results show that magnetic reconnection in the parsec-scale jet is a viable origin of the 2022--2023 TeV activity of NGC 1275, while better constraints on the gas density and jet power are needed to distinguish between leptonic and hadronic radiation channels.

astro-ph.HE↗

arXiv2025

The Stochastic Dissipation Model for the Steady State Neutrino and Multi-Wavelength Emission of TXS 0506+056

The blazar TXS 0506+056 has been suggested to be a potential high-energy neutrino source thanks to the observations of IceCube, which found outburst-like neutrino emissions during 2014-2015 and 2017 in the transient emission search, and a $3.5σ$ local significance in a 10-year time-integrated search. The conventional one-zone jet model cannot explain the observed neutrino flux during outbursts due to the constraint from the X-ray flux, leading to proposals of multi-zone models (e.g. two-zone model) with multiple radiation zones. In literature, it has been shown that multi-zone models may consistently explain the high-state neutrino emission and the multi-wavelength emission of TXS 0506+056, while the quasi-steady-state long-term emission has not been well studied. In this work, we investigate a physically based model for the quasi-steady-state neutrino and electromagnetic radiation under the same framework, and successfully reproduce the multi-messenger emission of TXS 0506+056.

astro-ph.HE↗

arXiv2024

A Unified Model for Multi-epoch Neutrino Events and Broadband Spectral Energy Distribution of $\rm TXS~0506+056$

The blazar $TXS~0506+056$ has been proposed as a high-energy neutrino emitter. However, it has been shown that the standard one-zone model cannot produce sufficiently high neutrino flux due to constraints from the X-ray data, implying more complex properties of the radiation zones in the blazar than that described by the standard one-zone model. In this work we investigate multi-epoch high-energy muon neutrino events associated with the blazar $TXS~0506+056$ occured in 2014-2015, 2017-2018, 2021-2022 and 2022-2023, respectively. We applied the so-called ``stochastic dissipation model'' to account for the neutrino-blazar associations detected in the four epochs simultaenously. This model describes a scenario in which the emission of the blazar arise from the superimposition of two components: a persistent component related to the quasi-stable state of the blazar and a transient component responsible for the sudden enhancement of the blazar's flux, either in electromagnetic radiation or in neutrino emission. The latter component could form at a random distance along the jet by a strong energy dissipation event. Under such assumption, the multi-epoch broadband spectral energy distribution (SED) can be well explained and the expected number of high-energy neutrino events is statistically realistic. The expected number of neutrino events in half-year is around 8.2, 0.07, 0.73 and 0.41, corresponding to the epoch in 2014-2015, 2017-2018, 2021-2022 and 2022-2023, respectively. Hence, our model self-consistently explains the episodic neutrino emission from $TXS~0506+056$.

astro-ph.HE↗

arXiv2022

On the Hadronic Origin of High Energy Emission of $γ$-ray Loud Narrow-Line Seyfert 1 PKS 1502+036

The radiation mechanism of Radio-Loud Narrow-Line Seyfert 1 (RL-NLS1) from X-ray to $γ$-ray bands remains an open question. While the leptonic model has been employed to explain the spectral energy distribution (SED), the hadronic process may potentially account for the high energy radiation of some $γ$-ray loud Narrow-Line Seyfert 1 (NLS1) as well. We study one of such RL-NLS1, PKS 1502+036, comparing the theoretical SEDs predicted by the leptonic model and the lepto-hadronic model to the observed one. For the hadronic processes, we take into account the proton synchrotron radiation and proton-photon interactions (including the Bethe-Heitler process and the photopion process) including the emission of pairs generated in the electromagnetic cascade initiated by these processes. Our results show that the leptonic model can reproduce the SED of this source, in which the X-ray to $γ$-ray radiation can be interpreted as the inverse Compton (IC) scattering. On the other hand, the proton synchrotron radiation can also explain the high energy component of SED although extreme parameters are needed. We also demonstrate that the $pγ$ interactions as well as the cascade process cannot explain SED. Our results imply that a leptonic origin is favored for the multi-wavelength emission of PKS 1502+036.

astro-ph.HE↗

arXiv2020

Diversity of gamma-ray and Radio Variabilities of Bright Blazars and Implications for gamma-ray Emission Location

Violent multi-wavelength variabilities are observed in gamma-ray-selected blazars. We present an analysis of long-term light curves for eight bright blazars to explore the co-variation pattern in the gamma-ray and radio bands. We extract their gamma-ray light curves and spectra with data observed by the Fermi/LAT since 2008. We find diverse co-variation patterns between the gamma-ray and radio (at 43 GHz) fluxes in these sources. The gamma-ray and radio fluxes of 3C 454.3 and PKS 1633+382 are correlated without any time-lag, suggesting that they are from the same radiation region. Similar correlation is also observed in 3C 273 and PKS 1222+216, but the radio flux is lag behind the gamma-ray flux approximately ~160 days and ~290 days, respectively. This likely suggests that their gamma-ray emission regions are located at the upstream of their radio cores at 43 GHz. The gamma-ray and radio fluxes of the other four blazars are not correlated, implying that the gamma-ray and radio emission may be from different regions in their jets. The gamma-ray light curves of the eight blazars can be decomposed into some long timescale variability components and fast spike flares. We propose that they may be attributed to the central engine activity and the magnetic reconnection process or turbulence in the local emission region, respectively.

astro-ph.HE↗

arXiv2020

Leptonic or Hadronic Emission: X-Ray Radiation Mechanism of Large-scale Jet Knots in 3C 273

A comprehensively theoretical analysis on the broadband spectral energy distributions (SEDs) of large-scale jet knots in 3C 273 is presented for revealing their X-ray radiation mechanism. We show that these SEDs cannot be explained with a single electron population model when the Doppler boosting effect is either considered or not. By adding a more energetic electron (the leptonic model) or proton (the hadronic model) population, the SEDs of all knots are well represented. In the leptonic model, the electron population that contributes the X-ray emission is more energetic than the one responsible for the radio-optical emission by almost two orders of magnitude; the derived equipartition magnetic field strengths (B_eq) are ~0.1 mG. In the hadronic model, the protons with energy of ~20 PeV are required to interpret the observed X-rays; the B_eq values are several mG, larger than that in the leptonic model. Based on the fact that no resolved substructures are observed in these knots and the fast cooling-time of the high-energy electrons is difficult to explain the observed X-ray morphologies, we argue that two distinct electron populations accelerated in these knots are unreasonable and their X-ray emission would be attributed to the proton synchrotron radiation accelerated in these knots. In case of these knots have relativistic motion towards the observer, the super-Eddington issue of the hadronic model could be avoided. Multiwavelength polarimetry and the gamma-ray observations with high resolution may be helpful to discriminate these models.

astro-ph.HE↗

arXiv2019

Magnetar as Central Engine of Gamma-Ray Bursts: Central Engine-Jet Connection, Wind-Jet Energy Partition, and Origin of Some Ultra-Long Bursts

Gamma-ray burst (GRB) central engines and jet production mechanisms are still open questions. Assuming that the shallow decay segments of canonical X-ray afterglow lightcurves of {\em Swift} GRBs are attributed to the magnetic dipole (MD) radiations of newly-born magnetars, we derive the parameters of the magnetars and explore their possible relations to jet and MD wind emission. We show that the magnetar initial spin period ($P_0$) are tightly correlated with the jet energy ($E_{\rm jet}$), which is almost proportional to the wind energy ($E_{\rm wind}$). Our least square fits yield $P_0\propto E^{-0.36\pm 0.03}_{\rm jet}$ and $E_{\rm wind}\propto E^{0.91\pm 0.07}_{\rm jet}$. These relations may imply that a magnetar with faster rotating speed can power a more energetic GRB, and energy partition between the jet and wind may be quasi-universal. Although the $P_0-E_{\rm jet}$ relation is driven by a few sub-energetic GRBs in our sample, our Monte Carlo simulation analysis shows that sample selection biases from instrumental flux limits and contaminations of the bright jet afterglows cannot make this correlation. Within this jet-wind paradigm, we propose that GRB 101225A-like ultra-long GRBs, whose prompt gamma-ray/X-ray lightcurves are featured as a long-lasting plateau with a sharp drop, may be the orphan MD wind emission being due to misalignment of their jet axis to the light of sight. Brief discussion on the orphan MD wind emission and its association with the gravitational wave radiation of newly-born magnetars is presented.

astro-ph.HE↗