Unraveling the broadband spectrum of B2 1308+326: A clue to its high energy emission mechanism

Abstract

The Flat Spectrum Radio Quasar (FSRQ) B2 1308+326 was in its highest $\gamma$-ray flaring state during 60260-60310 MJD. During this period, the source was detected in very high energy (VHE) by the large-sized telescope (LST-1). We conducted a detailed broadband spectral study of this source using the simultaneous data available in optical/UV, X-ray, and $\gamma$-ray bands. For the broadband spectral study, we select two gamma-ray high-flux states (59750-59800 MJD, 60260-60310 MJD) and one low-flux state (59250-59320 MJD). The broadband spectral energy distribution (SED) during these flux states are studied under leptonic emission scenario involving synchrotron, synchrotron self Compton (SSC) and external Compton (EC) processes. During the epochs, 59750-59800 MJD (high-flux state) and 59250-59320 MJD (low-flux state), the broadband SED is well fitted under the leptonic emission model while satisfying the equipartition between the particle and the magnetic field energy densities. However, the flaring state (60260-60310 MJD), during which the source showed VHE emission, demands deviation from equipartition by a factor of $\sim 14$ for the successful reproduction of the SED. This suggests the system may be under non-equilibrium condition or alternatively additional emission components may be active.