Search for serendipitous trans-Neptunian object occultation in X-rays

To study the population properties of small, remote objects beyond Neptune's orbit in the outer Solar system, of kilometre size or smaller, serendipitous occultation search is so far the only way. For hectometre-sized trans-Neptunian objects (TNOs), optical shadows actually disappear because of diffraction. Observations at shorter wavelengths are needed. Here, we report the effort of TNO occultation search in X-rays using Rossi X-ray Timing Explorer/Proportional Counter Array data of Sco X-1 taken from 2007 June to 2011 October. No definite TNO occultation events were found in the 334-ks data. We investigate the detection efficiency dependence on the TNO size to better define the sensible size range of our approach and suggest upper limits to the TNO size distribution in the size range from 30 to 300 m. A list of X-ray sources suitable for future larger facilities to observe is proposed.