# Study on Temporal and Spectral behavior of 3C 279 during 2018 January flare

## TL;DR

This study analyzes the 2018 January flare of blazar 3C 279 across multiple wavelengths, revealing temporal lags, spectral shifts, and correlations that suggest gamma-ray emission via Compton scattering of IR photons and increased jet Lorentz factors.

## Contribution

It provides a detailed multi-wavelength temporal and spectral analysis of 3C 279's flare, highlighting the spectral peak shift and its relation to flux variations, which is a novel insight.

## Key findings

- Detected a ~1 day lag between GeV energy bands.
- Observed asymmetry in gamma-ray light curves indicating spectral peak shifts.
- Correlated flux with spectral parameters, linking flux increase to higher Lorentz factors.

## Abstract

We present a detailed temporal and spectral study of the blazar 3C\,279 using multi-wavelength observations from Swift-XRT, Swift-UVOT and Fermi-LAT during a flare in 2018 January. The temporal analysis of $\gamma$-ray light curve indicates a lag of $\sim 1$ d between the 0.1--3 GeV and 3--500 GeV emission. Additionally, the $\gamma$-ray light curve shows asymmetry with slow rise--fast decay in energy band 0.1--3 GeV and fast rise--slow decay in the 3--500 GeV band. We interpret this asymmetry as a result of shift in the Compton spectral peak. This inference is further supported by the correlation studies between the flux and the parameters of the log-parabola fit to the source spectra in the energy range 0.1--500 GeV. We found that the flux correlates well with the peak spectral energy and the log-parabola fit parameters show a hard index with large curvature at high flux states. Interestingly, the hardest index with large curvature was synchronous with a very high energy flare detected by H.E.S.S. Our study of the spectral behavior of the source suggests that $\gamma$-ray emission is most likely to be associated with the Compton up-scattering of IR photons from the dusty environment. Moreover, the fit parameters indicate the increase in bulk Lorentz factor of emission region to be a dominant cause for the flux enhancement.