Multiwavelength spectral and temporal analysis of VHE Blazar 1ES 1959+650: Tracing emission mechanisms across flux states

TL;DR

This study analyzes multiwavelength data of blazar 1ES 1959+650 to understand its emission mechanisms across different flux states, revealing variability patterns and physical parameter trends consistent with shock-driven particle acceleration.

Contribution

It provides a comprehensive spectral and temporal analysis using multiwavelength data and models the emission with a one-zone SSC framework across flux states, highlighting physical parameter evolution.

Findings

Gamma-ray variability is largest, followed by X-ray and UV/optical.

X-ray spectra show a harder-when-brighter trend.

Physical parameters like Lorentz factor increase with flux.

Abstract

The high-synchrotron-peaked BL Lac object 1ES\,1959+650 exhibited pronounced activity between MJD~60310 -- 60603, including a very high energy (VHE) detection reported by LHAASO. To investigate the underlying emission mechanisms, we performed a comprehensive temporal and spectral analysis using multiwavelength data from \textit{Swift}-XRT/UVOT and \textit{Fermi}-LAT, covering the optical/UV to GeV $\gamma$-ray bands. The source shows strong energy-dependent variability, with the largest fractional variability in $\gamma$-rays, followed by X-rays and UV/optical, consistent with leptonic emission scenarios. Based on the variability patterns, we identified distinct flux states (F1, F2, F3, F4, F5, VHE-FX1, and VHE-FX2). The X-ray spectra exhibit a clear ``harder-when-brighter'' trend across these states. We modeled the broadband spectral energy distributions (SEDs) using a one-zone model incorporating synchrotron and synchrotron self-Compton (SSC) emission, implemented in \textsc{xspec} using $\chi^{2}$ minimization. During the VHE detection, the corresponding X-ray/optical emission likely resembled the F2 state. Modeling the VHE SED using F1-state data led to an SSC overprediction of the VHE flux, whereas all other states were well described within the one-zone framework. Systematic trends in physical parameters are observed across flux states, including spectral hardening, increasing break energy, rising bulk Lorentz factor, and decreasing magnetic field with increasing flux. These results suggest that enhanced particle acceleration efficiency and stronger Doppler boosting drive the observed flaring activity, while the decrease in magnetic field indicates conversion of magnetic energy into particle kinetic energy, consistent with shock-driven scenarios.