Radiation Mechanisms and Physical Properties of GeV $\gamma $-Ray Source GB 1310+487

Abstract

With the adoption of the synchrotron self-Compton (SSC) + external Compton (EC) model, investigation has been conducted on the radiation mechanisms of the GeV-bright active galaxy GB 1310+487 through modeling its quasi-simultaneous spectral energy distributions in active and quiescent states. We find that from the flare states to the post-flare state, the magnetic field (B) has experienced a gradual increase, whereas the electron spectrum's prefactor (N 0 ) and break energy ( br g ) decrease accordingly. The model indicates that the energy of the Poynting flux may be used to accelerate electrons. As for the GeV emission in the source, it is dominated by the EC process while the SSC contribution is negligible. Varying energy distribution of the emitting electrons, rather than location of the radiation blob, appears to be the driving factor for the observed changes in EC emission. Despite the similar total jet power and the same likely energy carrier (cold protons), the radiation efficiency of GB 1310+487 is lower than what is found in bright Fermiblazars.

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

“…The magnetic energy increase and matter energy decrease, which suggest an effective acceleration of the emitting electrons takes place at the expense of energy of the magnetic field. It might indicate that the reduced energy of the Poynting flux is used to accelerate electrons (Yang & Zhou 2016). Which may be one of the major factors to induce the observed activity of the GB 1310+487 by a conversion from magnetic energy to the energy of the radiating electrons.…”

“…The absorption of the foreground galaxy would result in the optical spectrum "redder" (thus forming the steep spectrum) and the X-ray spectrum "harder". Which complicates the interpretation of the SED, the model fitting parameters might be affected by the absorption of the foreground galaxy, especially in the optical part of the spectrum (e.g., the larger than usual value of p 2 )(e.g., Sokolovsky et al 2014;Yang & Zhou 2016). The large number of free parameters may also affect the model parameters constraints, particularly in the case of a possible degeneracy in the model; or the model used in the work is a too simplistic model for this problem.…”

“…In the EC process the external soft photons come from two emission region (e.g., both BLR and dusty torus; e.g., Dermer et al 2014;Yan et al 2015;Paliya et al 2015). Since the location of the γ-ray emission region is still unclear, different from Yang & Zhou (2016) the external seed photons are considered to originate from one single region (e.g., BLR or dust tours), we assume a dual-component Comptonscattering scenario in which the external seed photons predominantly originate from both the BLR and the dust torus, where the gamma-ray emission region locate outside the broad-line region and within the dusty torus.…”

“…In order to reduce the number of free parameters, the radius of the emitting region in the jet frame can be constrained with the minimum variability timescale and redshift with R δct var /(1 + z) ∼ 1.58 × 10 15 δ cm, where the timescale of variability of the γ-ray observations of Fermi is about half a day (Sokolovsky et al 2014). A conservative estimate of 1 day is adopted (Yang & Zhou 2016). The typical γ min = 40 (e.g., Kang et al 2014a;Zhang et al 2014) and γ max = 1 × 10 8 (γ max >> 100γ b ) are adopted in our fitting, which will not affect our main results (e.g., Kang et al 2016).…”

“…The γ-ray spectrum is a varying contribution from multiple EC components (e.g., EC on accretion disk and dusty torus photons or EC on BLR and dusty torus photons; e.g., Brown 2013;Dermer et al 2014;Yan et al 2015;Paliya et al 2015;Zheng et al 2017). Yang & Zhou (2016) employed a synchrotron + SSC + EC model to investigate the gamma-ray origin of the GeV-bright active galaxy GB 1310+487 through modeling its quasi-simultaneous SEDs in active and quiescent states. They proposed that the GeV gamma-ray emission of GB 1310+487 is dominated by the EC process scattering external soft photons coming from a simple blackbody radiation spectrum with a characteristic temperature T ext ∼ 11.2 eV.…”