Modeling the spectral-energy-distribution of 3C 454.3 in a "flat"
  broad-line-region scenario
  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 $4.4\times 10^{9}$\,$M_{\odot}$.
