Broad-band spectral and temporal study of OP 313 during its 2025 January very high energy flare

Abstract

We present a comprehensive broadband temporal and spectral analysis of the transition blazar OP 313 using Swift and Fermi-LAT observations obtained during its recent very high energy (VHE) flaring activity. The one-day binned γ-ray light curve displays multiple substructures with both symmetric and asymmetric profiles. Notably, it does not show the typical harder when brighter trend commonly observed in many blazars. The fractional variability across wavelengths exhibits a behaviour more consistent with BL Lac type sources. To investigate the origin of the VHE emission, we construct a broadband spectral energy distribution (SED) around the flaring epoch and model it using both leptonic and lepto-hadronic scenarios. The leptonic framework fails to account for the observed VHE flux, whereas the lepto-hadronic model provides a satisfactory description of this emission. These results highlight the importance of multi-wavelength coverage and hybrid emission models in interpreting extreme γ-ray activity in transition blazars.