Observations of fragments split from nucleus B of comet 73P/Schwassmann-Wachmann 3 with Subaru telescope

We observed the nucleus B of Comet 73P/Schwassmann-Wachmann 3 on 2006 May 3, UT with a wide-field camera Suprime-Cam of the Subaru Telescope just before the closest approach to the Earth on 2006 May 12, UT. Since the fragmentation of nucleus B was reported in April of 2006, fresh fragments were expected to be detected. A total of 54 fragments were discovered within a 1′.60 × 1′.13 region, southwest of nucleus B. Carrying out aperture photometry for the fragments, we obtained the power-law index of the cumulative luminosity function, α = 0.222. If we assume that the CCD flux of a fragment is proportional to the cross section, the equation q = 5α + 1 can be derived, where q is the power-law index of the cumulative size distribution, and therefore q = 2.1. Due to the large FOV of the camera (34′ × 27′), we might also be able to find fragments split from nucleus B before the perihelion passage in 2006. Upon searching for such fragments in the image, no object was found; since the approximate limiting magnitude is 24.2 mag, a bare nucleus (i.e., non-active comet) with 13.3m in radius could be detected in the image; however, the real detection limit should be less than a radius of 13.3m, because a comet at the same heliocentric distance as nucleus B of 1.1 AU would be active, and an active comet whose magnitude is 24.2 mag has a smaller nucleus than 13.3 m in radius due to the brightness of the dust coma.