Broadband imaging and narrowband polarimetry of comet 73P/Schwassmann-Wachmann 3, components B and C, on 3, 4, 8, and 9 May 2006

Context.The Jupiter family comet 73P/Schwassmann-Wachmann 3 (SW3) split into several pieces in 1995. Some of the original fragments were observed during the next apparition of the comet in 1999-2001. The last return of the comet in 2005-2006 was accompanied by tremendous further splitting of some SW3 components – in particular component B – into a large number of subfragments. Aims.We present observations of components B and C during their closest approach to Earth in the first half of May 2006. These results aim at characterizing the properties of dust particles released from the fragments of comet SW3 and at identifying dusty and gaseous structures in the comae and tail regions of components B and C, which could be useful for conclusions about the presence of active regions and break-up events of the components. Methods.We used narrowband imaging polarimetry and an analysis of the broadband surface brightness for the characterization of the dust comae of the SW3 components. Coma and tail structures in components B and C were enhanced by numerical methods. Results.The degree of linear polarization of components B and C follows the empirical phase-angle dependence as derived from other comets. Fragment B was found in outburst on May 8. The brightness outburst was accompanied by changes in the shape of the coma. During the outburst, the spatial distribution of the linear polarization showed some peculiarities that had disappeared again on May 9. Arc-like signatures of a temporary nature, typical of fragmentation events, are seen in broadband filter images of component B on 3, 8, and 9 May 2006. The secondary dust tail, seen in component B on 3 and 4 May 2006, marks the synchrone of an earlier splitting event around 25 April 2006. Fan-like coma structures are found in the sunward coma hemisphere of components B and C that might be related to localized enhanced activity on the rotating nuclei.