Dust properties and their variations in comet C/2013 X1 (PANSTARRS)

Context. We analyze the results of photometric monitoring of comet C/2013 X1 (PANSTARRS) from December 2015 until January 2016 obtained within B, V, and R Johnson–Cousins filters.Aims. The main objective is to investigate the dust coma and to obtain the physical characteristics of its dust particles.Methods. We analyzed our observations using model-agglomerated debris particles, and we constrained the microphysical properties of the dust in comet C/2013 X1 (PANSTARRS) on the pre-outburst and post-outburst epochs. Moreover, we applied a geometrical model to the images processed by digital filters to estimate the rotational period of the nucleus.Results. Our campaign revealed a sharp increase in the comet brightness on January 1, 2016. The B − V and V − R colors calculated within an aperture size of 17 000 km appear to be mostly red, except for the outburst date. The dust production (A f ρ proxy) and normalized spectral gradient S′ (B − R) dramatically changed on January 2 as compared to what was seen in December 2015. According to this model, the C/2013 X1 coma was populated by 70% organic-matter particles by volume and by two types of silicate particles together, constituting the other 30%. One type of silicate particles was composed of Mg-rich silicates, whereas the other type was composed of both Mg-rich and Fe-poor silicates. Using the geometrical model, we estimate the nucleus rotational period to be (24.02 ± 0.02) h. We interpret the observed coma morphology by two jet structures, one structure that formed by the near-pole active area at a latitude of (85_{+5^{−3)°, and the other structure formed by an active area at a latitude of (+40 ± 5)°.}}