  A thin, bright dust cloud, which is associated with the Rosetta mission
target object (67P/Churyumov-Gerasimenko), was observed after the 2002
perihelion passage. The neckline structure or dust trail nature of this cloud
is controversial. In this paper, we definitively identify the dust trail and
the neckline structure using a wide-field CCD camera attached to the Kiso
1.05-m Schmidt telescope. The dust trail of 67P/Churyumov-Gerasimenko was
evident as scattered sunlight in all images taken between September 9, 2002 and
February 1, 2003, whereas the neckline structure became obvious only after late
2002.
  We compared our images with a semi-analytical dynamic model of dust grains
emitted from the nucleus. A fading of the surface brightness of the dust trail
near the nucleus enabled us to determine the typical maximum size of the
grains. Assuming spherical compact particles with a mass density of 103 kg m-3
and an albedo of 0.04, we deduced that the maximum diameter of the dust
particles was approximately 1 cm. We found that the mass-loss rate of the comet
at the perihelion was 180 +/- 50 kg s-1 on or before the 1996 apparition, while
the mass-loss rate averaged over the orbit reached 20 +/- 6 kg s-1. The result
is consistent with the studies of the dust cloud emitted in the 2002/2003
return. Therefore, we can infer that the activity of 67P/Churyumov-Gerasimenko
has showed no major change over the past dozen years or so, and the largest
grains are cyclically injected into the dust tube lying along the cometary
orbit.
