A Subaru Pencil-beam Search for m_R~27 Trans-neptunian bodies

We present the results of an archival search for Trans-neptunian objects (TNOs) in an ecliptic field observed with Subaru in 2002. The depth of the search allowed us to find 20 new TNOs with magnitudes between R=24 and 27. We fit a double power law model to the data; the most likely values for the bright and faint power law exponents are alpha_1=0.73_{-0.09}^{+0.08} and alpha_2=0.20_{-0.14}^{+0.12}; the differential number density at R=23 is sigma_{23}=1.46_{-0.12}^{+0.14} and the break magnitude is R_{eq}=25.0_{-0.6}^{+0.8}. This is the most precise measurement of the break in the TNO luminosity function to date. The break in the size distribution corresponds to a diameter of D = 90+-30 km assuming a 4% albedo.