An upper limit on the abundance of small trans-Neptunian objects from X-ray occultations

Abstract

I describe the detection of 201 highly significant dips in the count rate of Sco X-1 from a search of some 500 ks of archival RXTE PCA data, which could be caused by TNO occultations. I show that most of these dips are correlated with particle showers in the PCA, suggesting that the dips in count rate result from large amounts of charge built up in the detectors. From the distribution of particle counts in the PCA and examination of asymmetry in individual dip profiles, I establish that at most ~ 6 of these dip events can be caused by occultations. This gives an upper limit on the cumulative TNO size distribution for > 20 m radius. I also derive a model lightcurve for occultations of Sco X-1 from diffraction theory, and use this model to predict properties of an ensemble of occultation events. Implications for future work are discussed.