arXiv subjects

Zhong-Hui Fan

Publications and source records attributed to Zhong-Hui Fan.

3 recordsLinked to original sources

arXiv2008

Stochastic Electron Acceleration in Shell-Type Supernova Remnants

We study the stochastic electron acceleration by fast mode waves in the turbulent downstream of weakly magnetized collisionless astrophysical shocks. The acceleration is most efficient in a dissipative layer, and the model characteristics are determined by the shock speed, density, magnetic field, and turbulence decay length. The model explains observations of shell-type supernova remnants RX J1713.7-3946 and J0852.0-4622 and can be tested by observations in hard X-rays with the HXMT and NuSTAR or gamma-rays with the GLAST.

astro-ph↗

arXiv2007

Stochastic Acceleration in the Western Hotspot of Pictor A

Chandra's high resolution observations of radio galaxies require a revisit of the relevant electron acceleration processes. Although the diffusive shock particle acceleration model may explain spectra of spatially unresolved sources, it encounters difficulties in explaining the structure and spectral properties of recently discovered Chandra X-ray features in several low-power radio sources. We argue that these observations strongly suggest stochastic electron acceleration by magnetized turbulence, and show that the simplest stochastic particle acceleration model with energy independent acceleration and escape timescales can overcome most of these difficulties. We use the bright core of the western hotspot of Pictor A as an example to demonstrate the model characteristics, which may be tested with high energy observations.

astro-ph↗

arXiv2003

Black hole masses and Doppler factors of $γ$-ray active galactic nuclei

The sizes of the broad-line regions (BLRs) in $γ$-ray active galactic nuclei (AGNs) are estimated from their optical continuum luminosity by using the empirical relation between $R_{\rm BLR}$ and $L_{λ,\rm opt}$. Using the broad emission line data, we derive the photon energy density in the relativistic blobs near the massive black holes in AGNs. We calculate the power of the broad-line photons Compton up-scattered by the relativistic electrons in the blobs. Compared with observed $γ$-ray emission data, the Doppler factors $δ$ of the blobs for a sample of 36 $γ$-ray AGNs are derived, which are in the range of $\sim 3-17$. We estimate the central black hole masses of these $γ$-ray AGNs from the sizes of the BLR and the broad line widths. It is found that the black hole masses are in the range of $\sim 10^{8}-10^{10}M_{\odot}$. A significant correlation is found between the Doppler factor $δ$ and the core dominance parameter $R$. The results are consistent with the external radiation Compton (ERC) models for $γ$-ray emission from AGNs. The soft seed photons are probably from the broad-line regions.

astro-ph↗