Constraints on the Location of the Gamma-ray Emission Region for the Gamma-ray-loud Radio Source GB 1310+487

We employ a single-zone leptonic jet model, with synchrotron, synchrotron self-Compton, and external Compton (EC) processes, to reproduce the quasi-simultaneous multi-wavelength spectral energy distributions in active and quiescent states of the narrow-line gamma-ray-loud radio source GB 1310+ 487. In the case of the EC process, the external seed photons from both the. broad line region (BLR) and the. dust torus are considered by assuming that the gamma-ray emission region is located at the outside boundary of the BLR and inside the dust torus. Comparing the energy density of external photon fields U-BLR obtained by model fitting with that constrained from the BLR observations. We find that the location of the gamma-ray-emitting region of GB 1310+ 487 can be tightly constrained at the outer edge of the BLR (the dissipation distance of the gamma-ray emission region from central black hole rdiss similar to a few times of RBLR). The ratio of magnetic energy and emitting-electron energy in the radiation blob (is an element of(B)= L-B/L-e) is gradually increased from Flare 1, to. Flare 2, to Post-flare, where the magnetic energy increases and the matter energy decreases. These results suggest that the conversion of the magnetic field and the matter (radiation electrons) energy and the location of the gamma-ray emission region (or ambient photon field) may play an important role in different radiation states of GB 1310+ 487.