Search for comet-like activity in asteroid 7968 Elst-Pizarro and limitation of its rotational pole orientation

We present the results of a new investigation of the asteroid-comet transition object or activated asteroid 7968 Elst-Pizarro (133P/Elst-Pizarro). We performed Cousins R-band CCD imaging observations on UT 16 January, 28 February and 1 March 2005 in order to search for comet-like activity of this activated asteroid. These observations do not show any comet-like activity shuch as coma, tail(s) or a dust trail. The object was at large heliocentric distances between 3.623 and 3.647 AU a few months after its aphelion. Taking into account the seasonal modulation model to explain the activity, the distribution of the active/inactive phases along its orbit, and the available lightcurve observations of Elst-Pizarro, we propose four working models for the possible orientation of its rotational pole. These four best fit working models for the pole orientation of Elst-Pizarro are in a good agreement with the observed data. The true direction of the rotational pole is still unknown.