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We present a detailed temporal and spectral study of the blazar 3C\,279 usingmulti-wavelength observations from Swift-XRT, Swift-UVOT and Fermi-LAT during aflare in 2018 January. The temporal analysis of $\gamma$-ray light curveindicates 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--fastdecay in energy band 0.1--3 GeV and fast rise--slow decay in the 3--500 GeVband. We interpret this asymmetry as a result of shift in the Compton spectralpeak. This inference is further supported by the correlation studies betweenthe flux and the parameters of the log-parabola fit to the source spectra inthe energy range 0.1--500 GeV. We found that the flux correlates well with thepeak spectral energy and the log-parabola fit parameters show a hard index withlarge curvature at high flux states. Interestingly, the hardest index withlarge curvature was synchronous with a very high energy flare detected byH.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 Comptonup-scattering of IR photons from the dusty environment. Moreover, the fitparameters indicate the increase in bulk Lorentz factor of emission region tobe a dominant cause for the flux enhancement.

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