  Beginning in March 2014, the OSIRIS (Optical, Spectroscopic, and Infrared
Remote Imaging System) cameras began capturing images of the nucleus and coma
(gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle
camera (WAC) and the narrow angle camera (NAC). The many observations taken
since July of 2014 have been used to study the morphology, location, and
temporal variation of the comet's dust jets. We analyzed the dust monitoring
observations shortly after the southern vernal equinox on May 30 and 31, 2015
with the WAC at the heliocentric distance Rh = 1.53 AU, where it is possible to
observe that the jet rotates with the nucleus. We found that the decline of
brightness as a function of the distance of the jet is much steeper than the
background coma, which is a first indication of sublimation. We adapted a model
of sublimation of icy aggregates and studied the effect as a function of the
physical properties of the aggregates (composition and size). The major finding
of this article was that through the sublimation of the aggregates of dirty
grains (radius a between 5 microm and 50 microm) we were able to completely
reproduce the radial brightness profile of a jet beyond 4 km from the nucleus.
To reproduce the data we needed to inject a number of aggregates between 8.5 x
$10^{13}$ and 8.5 x $10^{10}$ for a = 5 microm and 50 microm respectively, or
an initial mass of $H_2O$ ice around 22kg.
