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Hard-TeV BL Lac objects are newly identified populations of active galactic nuclei with the emitted γ-ray photons well above TeV energies. In this paper, we explain the multiwavelength emission of six Hard-TeV BL Lac objects by using a truncated conical emission region of the jet, where the electron distribution is obtained by numerically solving the evolution equation along the jet self-consistently. For comparison, we also apply the model to Mrk 421 and Mrk 501, which are the potential candidates for the hard TeV emissions. We demonstrate that the model can satisfactorily reproduce the spectral energy distributions of eight sources, particularly of six Hard-TeV sources, where no extreme minimum Lorentz factor of the electron population is required. In contrast with Mrk 421 and Mrk 501, six Hard-TeV sources have rather low magnetization in emitting regions and high cutoff energies of the electron distributions.

We propose a two-zone synchrotron self-Compton (SSC) model, including an inner gamma-ray emitting region with spherical shape and a conical radio emitting region located at the extended jet, to alleviate the long-standing "bulk Lorentz factor crisis" in blazars. In this model, the spectral energy distributions (SEDs) of blazars are produced by considering the gamma-ray emitting region inverse Compton scattering of both the synchrotron photons itself and the ambient photons from the radio emitting region. Applying the model to Mrk 501, we obtain that the radio emitting region has a comoving length of similar to 0.15 pc and is located at sub-parsec scale from the central engine by modeling the radio data; the flux of the Compton scattering of the ambient photons is so low that it can be neglected safely. The characteristic hard gamma-ray spectrum can be explained by the superposition of two SSC processes, and the model can approximately explain the very high energy (VHE) data. The insights into the spectral shape and the inter-band correlations under the flaring state will provide us with a diagnostic for the bulk Lorentz factor of radio emitting region, where the low and upper limits of 8 and 15 are preferred, and for the two-zone SSC model itself. In addition, our two-zone SSC model shows that the gamma-ray emitting region creates flare on the timescale of merely a few hours, and the long time outbursts more likely originate from the extended radio emitting region.

4C +21.35 is a flat-spectrum-radio-quasar-type blazar, in which the rapid variability of very high energy (VHE, $E_{\gamma}\gtrsim 100$\,GeV) emission as short as $\sim$ 10 minutes was observed by MAGIC Cherenkov telescopes, and the VHE spectrum extends up to at least 400\,GeV. In this paper, by using a flat broad-line region (BLR) structure, we study the location and properties of $\gamma$-ray emitting region of 4C +21.35 under the constraints of multiwavelength data. We fit three quasi-simultaneous spectral energy distributions (SEDs) using homogeneous one-zone leptonic model, in which the flat BLR with the aperture angle of $\alpha=25^{\circ}$ and a spherically symmetric hot dusty torus with the temperature of $T_{\rm sub}=1200$\,K, are assumed. The results show that the jet structure of 4C +21.35 is nearly conical with a half-opening angle of $\theta_{\rm j}\simeq 0.29^{\circ}-0.6^{\circ}$. Furthermore, the emitting region is located within the BLR clouds and approaches to outer radius of the BLR during the flaring states, while it is well beyond the dusty torus in quiescent state. The quiescent high-energy emission is dominated by synchrotron self-Compton (SSC) process, the high-energy emission during the flaring periods is dominated by Compton scattering of BLR and dusty torus photons with the value of Compton-dominance parameter is about 30. Moreover, the fit to optical/ultraviolet data provides a further support that the central black hole (BH) mass of 4C +21.35 is $6\times 10^{8}$\,$M_{\odot}$., Comment: 15 Pages, 7 figures, accepted for publication in Publications of the Astronomical Society of Japan

The broad-line region (BLR) of flat-spectrum radio quasars (FSRQs) could have a "flat" geometrical structure to allow GeV gamma-ray photons escape, to produce the observed gamma-ray flares with short timescales. In this paper, we collect the quasi-simultaneous spectral energy distributions (SEDs) of the FSRQ 3C 454.3 obtained by the multi-wavelength campaigns spanning from 2007 July to 2011 January, and use a model with the "flat" structure BLR, the accretion disc and the dust torus to explain the SEDs of gamma-ray outbursts. We obtain the following results: (i) The jet is almost in equipartition between magnetic and particle energy densities during the outbursts; (ii) When the emitting region locates inside the cavity of the BLR, the covering factor $f_{\rm BLR}$ of the BLR is very small; as the emitting region goes into the BLR structure, $f_{\rm BLR}$ increases. (iii) The aperture angle $\alpha$ describing the BLR structure is about $45^{\circ}$; (iv) The central black hole (BH) mass is about $5\times 10^{8}$\,$M_{\odot}$ rather than $4.4\times 10^{9}$\,$M_{\odot}$., Comment: 21 pages, 29 figures. Accepted for publication by PASJ

The broad-line region (BLR) is an important component of blazars, especially for the flat spectrum radio quasars (FSRQs). The soft photons arising from the BLR will substantially affect the transparency of the gamma-ray photons produced in the relativistic jet. In the paper, we study the effect of the geometrical structure of the BLR on the absorption of gamma-rays. We find that the gamma-ray optical depth strongly depends on the geometrical structure of the BLR. For a "flat" geometry of the BLR, the gamma-ray photons with specified energies could escape transparently even their emission region locates inside the cavity of the BLR., 16 pages, 7 figures, accepted by PASJ