Revisiting the flaring activity in early 2015 of BL Lacertae object S5 0716+714

TL;DR

This study analyzes multi-wavelength data of the BL Lac object S5 0716+714 during a 2015 flare, comparing different emission models to understand its broadband spectral energy distribution and emission mechanisms.

Contribution

It evaluates three one-zone models (SSC, SSC+EC, SSC+pp) for fitting the SEDs of S5 0716+714 during a flare, highlighting the strengths and limitations of each model.

Findings

SSC model fits SEDs but requires extreme Doppler factors.

SSC+EC model fits SEDs with weak external photon fields but high Doppler factors.

SSC+pp model reproduces SEDs with jet power exceeding Eddington luminosity.

Abstract

In this work, we analyzed multi-wavelength data of the BL Lac object S5 0716+714 to investigate its emission mechanisms during a flaring state observed in early 2015. We examined the temporal behavior and broadband spectral energy distributions (SEDs) during the flare. The size of the $\gamma$-ray emission region was estimated based on the variability timescale. To explore the multi-wavelength properties of S5 0716+714, we employed three one-zone models: the SSC model, the SSC plus EC model, and the SSC plus pp interactions model, to reproduce the SEDs. Our findings indicate that while the SSC model can describe the SEDs, it requires an extreme Doppler factor. In contrast, the SSC plus EC model successfully fits the SEDs under the assumption of weak external photon fields but requires a high Doppler factor. Additionally, the SSC plus interactions model also reproduces the SEDs, with $\gamma$-ray emission originating from $\pi^{0}$ decay. However, this model leads to a jet power that exceeds the Eddington luminosity, which remains plausible due to the flaring state or the presence of a highly collimated jet.