Haocheng Zhang - Ohio University, USA

Haocheng Zhang
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Name
Haocheng Zhang
Affiliation
Ohio University, USA
City
Athens
Country
United States

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Pub Categories

 
High Energy Astrophysical Phenomena (10)
 
Physics - Space Physics (1)
 
Solar and Stellar Astrophysics (1)
 
Physics - Plasma Physics (1)

Publications Authored By Haocheng Zhang

2016Dec
Affiliations: 1University of New Mexico, 2Los Alamos National Lab, 3Los Alamos National Lab, 4University of New Mexico

Kink instabilities are likely to occur in the current-carrying magnetized plasma jets. Recent observations of the blazar radiation and polarization signatures suggest that the blazar emission region may be considerably magnetized. While the kink instability has been studied with first-principle magnetohydrodynamic (MHD) simulations, the corresponding time-dependent radiation and polarization signatures have not been investigated. Read More

2016Jul
Affiliations: 1University of New Mexico, 2Ohio University, 3North-West University, Potchefstroom, South Africa

We present a newly developed time-dependent three-dimensional multi-zone hadronic blazar emission model. By coupling a Fokker-Planck based lepto-hadronic particle evolution code 3DHad with a polarization-dependent radiation transfer code, 3DPol, we are able to study the time-dependent radiation and polarization signatures of a hadronic blazar model for the first time. Our current code is limited to parameter regimes in which the hadronic $\gamma$-ray output is dominated by proton synchrotron emission, neglecting pion production. Read More

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 $\gamma$-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. Read More

2015Dec
Affiliations: 1Ohio University, 2University of Nevada, Las Vegas, 3Los Alamos National Lab, 4North-West University, Potchefstroom, South Africa

The optical radiation and polarization signatures in blazars are known to be highly variable during flaring activities. It is frequently argued that shocks are the main driver of the flaring events. However, the spectral variability modelings generally lack detailed considerations of the self-consistent magnetic field evolution modeling, thus so far the associated optical polarization signatures are poorly understood. Read More

Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux dominated flows. In this letter, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically-dominated ion-electron plasma using fully kinetic simulations. For an ion-electron plasma with the total magnetization $\sigma_0=B^2/(4\pi n(m_i+m_e)c^2)$, the magnetization for each species is $\sigma_i \sim \sigma_0$ and $\sigma_e \sim (m_i/m_e) \sigma_0$, respectively. Read More

2015Jul
Affiliations: 1TIFR, Mumbai, India, 2LANL, Los Alamos, USA, 3TIFR, Mumbai, India, 4TIFR, Mumbai, India, 5NWU, Potchefstroom, South Africa, 6PRL, Ahmedabad, India, 7PRL, Ahmedabad, India

We present a detailed investigation of the flaring activity observed from a BL Lac object, S5 0716+714 , during its brightest ever optical state in the second half of January 2015. Observed almost simultaneously in the optical, X-rays and {\gamma}-rays, a significant change in the degree of optical polarization (PD) and a swing in the position angle (PA) of polarization were recorded. A detection in the TeV (VHE) was also reported by the MAGIC consortium during this flaring episode. Read More

2015Feb
Affiliations: 1Ohio University, 2University of Potsdam, Germany, 3North-West University, Potchefstroom, South Africa, 4Los Alamos National Lab, 5Los Alamos National Lab

The polarization signatures of the blazar emissions are known to be highly variable. In addition to small fluctuations of the polarization angle around a mean value, sometimes large (> 180^o) polarization angle swings are observed. We suggest that such p henomena can be interpreted as arising from light-travel-time effects within an underlying axisymmetric emission region. Read More

We perform time-dependent, spatially-resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts for light-travel-time effects and is applied to flares observed in the flat spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/{\gamma}-ray correlation at some times, but orphan optical flares at other times. Changes in both the magnetic field and the particle acceleration efficiency are explored as causes of flares. Read More

2014Jan
Affiliations: 1Ohio University, LANL, 2Univ. of Potsdam, DESY, 3North-West University, Ohio University

We present a detailed analysis of time- and energy-dependent synchrotron polarization signatures in a shock-in-jet model for gamma-ray blazars. Our calculations employ a full 3D radiation transfer code, assuming a helical magnetic field throughout the jet. The code considers synchrotron emission from an ordered magnetic field, and takes into account all light-travel-time and other relevant geometric effects, while the relevant synchrotron self-Compton and external Compton effects are taken care of with the 2D MCFP code. Read More

2013Jul
Affiliations: 1Ohio University, USA, 2North-West University, South Africa

We present a theoretical analysis of the expected X-ray and gamma-ray polarization signatures resulting from synchrotron self-Compton emission in leptonic models, compared to the polarization signatures from proton synchrotron and cascade synchrotron emission in hadronic models for blazars. Source parameters resulting from detailed spectral-energy-distribution modeling are used to calculate photon-energy-dependent upper limits on the degree of polarization, assuming a perfectly organized, mono-directional magnetic field. In low-synchrotron-peaked blazars, hadronic models exhibit substantially higher maximum degrees of X-ray and gamma-ray polarization than leptonic models, which may be within reach for existing X-ray and gamma-ray polarimeters. Read More