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Applying image processing and enhancement techniques to our CCD images we could investigate the structures of the inner coma of comet C/2013 X1; the dust tail and a broad fan-shaped structure that originated from a different area of the nucleus than the tail were clearly detected. The triangular shape of the fan suggested that it was the result of a continuous outflow of dust from a single active source located at mid-high latitude (about 60° on a supposed spherical nucleus) on the surface of the comet's nucleus oriented in sunward direction, and that the comet's spin axis was placed near the sky plane. This allowed us to estimate its orientation at RA 240°±10° (=16h00 m) and declination +00°±10°. The fan structure remained quite stable in the 4-months observation period, indicating that the comet's spin axis remained steadily lying near the sky plane; a slow clockwise rotation of the fan in sunward direction appeared to be directly connected with the geometrical conditions of observation. Differential photometry applied to the inner coma, near the cometary nucleus, showed a light curve with an amplitude of 0.053 magnitudes, characterized by a highly repetitive periodicity throughout the entire observation period, and most likely related to the comet's rotation period, estimated at 0.498±0.015 days. Computer simulations of the coma features, as well as of the tail and spin axis positions, are fairly comparable with our observations, confirming the correctness of the findings. [ABSTRACT FROM AUTHOR]

After the discovery of the breakup event of comet C/2011 J2 in August 2014, we followed the primary body and the main fragment B for about 120 days in the context of a wide international collaboration. From the analysis of all published magnitude estimates we calculated the comet׳s absolute magnitude H =10.4, and its photometric index n =1.7. We also calculated a water production of only 110 kg/s at the perihelion. These values are typical of a low-activity, long-period or new comet. Analysis of the motion of fragment B over the observation period showed that the first breakout event likely occurred between 12 July and 30 July 2014. Nucleus B remained persistently visible throughout the 4-month observation period. The projected separation velocity of nucleus B from the parent body was 4.22 m/s at the time of the breakup and 12.7 m/s at the end of the observation period, suggesting that nucleus B was subjected to a constant deceleration a = 6.87 ∙ 10 − 7 m / s 2 . The spin period of the main nucleus was estimated as 4.56 h±0.05 h by photometric analysis. The structural analysis of the comet showed a cohesive strength of the nucleus greater than ~0.9 kPa; assuming a bulk density of 500 kg/m 3 , with a rotation period of 4.56 h the cometary nucleus might have failed structurally, especially if the body was elongated. These results suggest that the nucleus of comet C/2011 J2 has an elongated shape, with a ratio of the semi-minor axis to the semi-major axis β < 0.675 ; the semi-major axis of the pristine nucleus could be larger than 8 km. From this study, we propose that rotational disruption, possibly combined with sublimation pressure, was a reasonable explanation for the breakup event in comet C/2011 J2. [ABSTRACT FROM AUTHOR]