Comet C/2012 X1 (LINEAR), long-periodic comet with initial period 1740 years, is one of most interesting comet at all. My light curve of this comet require 7 intervals with different photometric parameters.
Originally this comet probably started to brighten before its discovery in distance 5 AU from Sun, first month it seems that its brightness was increasing fast. Shortly after discovery, its brightening continue calmly following usual comet brightening slope.
After conjunction with Sun it was recovered nearly 6 mag (250 times) brighter then expected in distance 2.5 AU from Sun, brightening continued only for few weeks.
Then comet started to fade, apparently stepping back from its absolute magnitude peak. In distance 1.9 AU, brightening started again with usual comet brightening slope. Its activity was still almost 4 mag (40x) larger then pre-outburst values.
After perihelion passage, it fade very slowly for nearly 70 days its activity was not stepping back as expected. In distance 1.9 AU brightness started to decrease fast again until now.
Comet C/2012 X1 (LINEAR) is one of small portion comets with calculated non-gravitational parameters ( http://www.minorplanetcenter.net/db_search/show_object?utf8=%E2%9C%93&object_id=C%2F2012+X1 ), in this case they are very strong, suggesting that huge activity over large portion of surface was pushing relatively small nucleus against Sun direction.
Presence of NG elements allows us to estimate upper limit for comet nucleus mass which is 2.9 * 10^12 kg, assuming density 0.5 g/cm^3 it means a spherical nucleus with 2.2 km in diameter.
However estimated water production needs much more surface then spherical 2.2 km sized nucleus can provide, before major outburst, such nucleus could have active <5% surface, after-outburst activity needs much more then 100% of such surface.
This pointing to possibility, that after outburst, nucleus shape is extremely irregular and out-gassing from icy grains in coma is present. A fragmentation can also explain this, however no fragments was discovered so far.