arXiv subjects

Wen-Po Liu

Publications and source records attributed to Wen-Po Liu.

6 recordsLinked to original sources

arXiv2015

An asymmetrical synchrotron model for knots in the 3C 273 jet

To interpret the emission of knots in the 3C 273 jet from radio to X-rays, we propose a synchrotron model in which, owing to the shock compression effect, the injection spectra from a shock into the upstream and downstream emission regions are asymmetric. Our model could well explain the spectral energy distributions of knots in the 3C 273 jet, and predictions regarding the knots spectra could be tested by future observations.

astro-ph.HE↗

arXiv2015

An IC/CMB interpretation for the large-scale jet X-ray emission of 3C 273

We present that the model of inverse Compton scattering of cosmic microwave background photons (IC/CMB) could well explain the large-scale jet X-ray radiation of 3C 273, and does not violate new Fermi observations. For the individual knots, the synchrotron spectrum of the low-energy electrons responsible for the IC/CMB X-ray emission may be different from the extrapolation of the 10GHz radio spectrum of knots. Based on the IC/CMB model for the 3C 273 large-scale jet, the Fermi observations may mainly come from the small-scale jet of 3C 273 (i.e., the core). Future observations could examine our interpretation on the spectral energy distributions (SED) of knots and large-scale jet in 3C 273.

astro-ph.HE↗

arXiv2014

A Non-Mainstream Viewpoint on Apparent Superluminal Phenomena in AGN Jet

The group velocity of light in material around the AGN jet is acquiescently one (c as a unit), but this is only a hypothesis. Here, we re-derive apparent superluminal and Doppler formulas for the general case (it is assumed that the group velocity of light in the uniform and isotropic medium around a jet (a beaming model) is not necessarily equal to one, e.g., Araudo et al. (2010) thought that there may be dense clouds around AGN jet base), and show that the group velocity of light close to one could seriously affect apparent superluminal phenomena and Doppler effect in the AGN jet (when the viewing angle and Lorentz factor take some appropriate values).

astro-ph.HE↗

arXiv2013

An hourglass model for the flare of HST-1 in M87

To explain the multi-wavelength light curves (from radio to X-ray) of HST-1 in the M87 jet, we propose an hourglass model that is a modified two-zone system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or Laval nozzle-shaped layer connected by two revolving exponential surfaces surrounding a fast spine, through which plasma blobs flow. Based on the conservation of magnetic flux, the magnetic field changes along the axis of the hourglass. We adopt the result of TG08---the high-energy emission from GeV to TeV can be produced through inverse Compton by the two-zone system, and the photons from radio to X-ray are mainly radiated by the fast inner zone system. Here, we only discuss the light curves of the fast inner blob from radio to X-ray. When a compressible blob travels down the axis of the first bulb in the hourglass, because of magnetic flux conservation, its cross section experiences an adiabatic compression process, which results in particle acceleration and the brightening of HST-1. When the blob moves into the second bulb of the hourglass, because of magnetic flux conservation, the dimming of the knot occurs along with an adiabatic expansion of its cross section. A similar broken exponential function could fit the TeV peaks in M87, which may imply a correlation between the TeV flares of M87 and the light curves from radio to X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1 verifies our prediction based on the model fit to the main peak of the VLA 15 GHz radio light curve.

astro-ph.HE↗

arXiv2008

A Modified Stratified Model for 3C 273 Jet

We present a modified stratified jet model to interpret the observed spectral energy distributions of knots in 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 3C273 knots can be understood as a manifestation of deviation of the equivalent Doppler factor of stratified emission regions in individual knot from a characteristic one. The summed spectral energy distribution of all the ten knots in 3C 273 jet can be well fitted by two components, low-energy (radio to optical) component dominated by the synchrotron radiation and high-energy component (UV, X-ray and $γ$-ray) dominated by the inverse Compton scattering of the cosmic microwave background. This gives a consistent spectral index of $α=0.88$ ($S_ν\propto ν^{-α}$) and a characteristic Doppler factor of 7.4. Assuming the average of the summed spectrum as the characteristic spectrum of each knot in the 3C273 jet, we further get a distribution of Doppler factor. We discuss the possible implications of these results for the physical properties in 3C 273 jet. Future GeV observations with $\it GLAST$ could separate the $γ$-ray emission of 3C 273 from the large scale jet and the small scale jet (i.e. the core) through measuring the GeV spectrum.

astro-ph↗

arXiv2007

A Modified Synchrotron Model for Knots in the M87 Jet

For explaining the broadband spectral shape of knots in the M87 jet from radio through optical to X-ray, we propose a modified synchrotron model that considers the integrated effect of particle injection from different acceleration sources in the thin acceleration region. This results in two break frequencies at two sides of which the spectral index of knots in the M87 jet changes. We discuss the possible implications of these results for the physical properties in the M87 jet. The observed flux of the knots in the M87 jet from radio to X-ray can be satisfactorily explained by the model, and the predicted spectra from ultraviolet to X-ray could be further tested by future observations. The model implies that the knots D, E, F, A, B, and C1 are unlikely to be the candidate for the TeV emission recently detected in M87.

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