  The blazar 3C 279 exhibited a giant $\gamma$-ray outburst in 2013 December
and 2014 April. Apart from the very fast $\gamma$-ray flux variability, the
spectral nature of the flares were also found to vary significantly between
these two flaring events. A prominent curvature in the $\gamma$-ray spectrum
was noticed in 2014 April flare, on the other hand, the 2013 December displayed
an extreme hardening of the spectrum. These observations, thus, put strong
constraints on our understanding of the underlying particle acceleration
mechanisms.
