Serendipitous occultations by sub-kilometre-sized trans-Neptunian objects with MIOSOTYS - I

ABSTRACT We present here the first 4-yr (2010–2013) campaign of the search for sub-kilometre-sized trans-Neptunian objects using serendipitous method with a dedicated ground-based instrument miosotys (Multi-object Instrument for Occultations in the SOlar system and TransitorY Systems). The total observing time used to carry out this study is about $8.4 \times 10^{3}$ star-hours. We first applied a deviation method to reduced light curves to pre-select suspect flux drops. Then, we performed diffraction pattern fits on these using a data base of synthetic profiles to identify possible detections. Finally, we examined the likelihood of the possible detections and found five that passed all our tests, including one that may be a false positive. Therefore, our observations lead to four possible occultation events (POEs). From these detections, we work out a density in the ecliptic sky plane for TNOs larger than a radius of 540 m of $N(r>540\,\rm m)=1.0_{-6.4}^{+0.2} \times 10^7 \ \mathrm{deg}^{-2}$. Fitting this new TNO density to the assumed break $r_{\rm break} = 45$ km gives a power-law size distribution index $q \simeq 4.0 \pm 0.2$, consistent with the other two results already published in the literature at small sizes. Considering only these three studies to assess the possible slope of the distribution at small sizes, we find $q \simeq 1.1 \pm 0.4$ for radii between 250 and 540 m, flatter than predicted by theoretical models of the Kuiper belt evolution.