We report the discovery of a cold Super-Earth planet (m_p=4.4 +/- 0.5 M_Earth) orbiting a low-mass (M=0.23 +/- 0.03 M_Sun) M dwarf at projected separation a_perp = 1.18 +/- 0.10 AU, i.e., about 1.9 times the snow line. The system is quite nearby for a microlensing planet, D_Lens = 0.86 +/- 0.09 kpc. Indeed, it was the large lens-source relative parallax pi_rel=1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax" that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q < 1 * 10^-4. We apply a new planet-detection sensitivity method, which is a variant of "V/V_max", to seven of these eight planets to derive the mass-ratio function in this regime. We find dN/d(ln q) ~ q^p, with p = 1.05 (+0.78,-0.68), which confirms the "turnover" in the mass function found by Suzuki et al. relative to the power law of opposite sign n = -0.93 +/- 0.13 at higher mass ratios q >~ 2 * 10^-4. We combine our result with that of Suzuki et al. to obtain p = 0.73 (+0.42,-0.34).
@article{arxiv.1802.02582,
title = {OGLE-2017-BLG-1434Lb: Eighth q < 1 * 10^-4 Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function},
author = {A. Udalski and Y. -H. Ryu and S. Sajadian and A. Gould and P. Mróz and R. Poleski and M. K. Szymański and J. Skowron and I. Soszyński and S. Kozłowski and P. Pietrukowicz and K. Ulaczyk and M. Pawlak and K. Rybicki and P. Iwanek and M. D. Albrow and S. -J. Chung and C. Han and K. -H. Hwang and Y. K. Jung and I. -G. Shin and Y. Shvartzvald and J. C. Yee and W. Zang and W. Zhu and S. -M. Cha and D. -J. Kim and H. -W. Kim and S. -L. Kim and C. -U. Lee and D. -J. Lee and Y. Lee and B. -G. Park and R. W. Pogge and V. Bozza and M. Dominik and C. Helling and M. Hundertmark and U. G. Jørgensen and P. Longa-Peña and S. Lowry and M. Burgdorf and J. Campbell-White and S. Ciceri and D. Evans and R. Figuera Jaimes and Y. I. Fujii and L. K. Haikala and T. Henning and T. C. Hinse and L. Mancini and N. Peixinho and S. Rahvar and M. Rabus and J. Skottfelt and C. Snodgrass and J. Southworth and C. von Essen},
journal= {arXiv preprint arXiv:1802.02582},
year = {2018}
}