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 (SSC) and external Compton (EC) process, 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 broad line region (BLR) and 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 $U_{\rm BLR}$ 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 $r_{\rm diss} \sim {\rm~a~few~times~of}~R_{\rm BLR}$). The ratio of magnetic energy and emitting-electron energy in the radiation blob ($\epsilon_{B}=L_{B}/L_{\rm e}$) is gradually increased from Flare 1, Flare 2 to Post-Flare, where the magnetic energy increase and matter energy decrease. 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.