NEAR-INFRARED MICROLENSING OF STARS BY THE SUPERMASSIVE BLACK HOLE IN THE GALACTIC CENTER

摘要

We investigate microlensing amplification of faint stars in the dense stellar cluster in the Galactic center by the supermassive black hole, which is thought to coincide with the radio source Sgr A*. Such amplification events would appear very close to the position of Sgr A* and could be observed, in prin- ciple, during the monitoring of stellar proper motions in the Galactic center. We use observations of the near-infrared K-band (2.2mu m) luminosity function in the Galactic center and in Baade's window, as well as stellar population synthesis computations, to construct empirical and theoretical K luminosity function models for the inner 300 pc of the Galaxy. These, together with the observed dynamical properties of the central cluster and inner bulge, are used to compute the rates of microlensing events that amplify stars with different intrinsic luminosities above specified detection thresholds. We present computations of the lensing rates as functions of the event durations, which range from several weeks to a few years, for detection thresholds ranging from Ko = 16 to 19 mag. We find that events with durations shorter than a few months dominate the lensing rate because of the very high stellar densities and velocities very near the black hole, where the effective lens size is small. For the current detection limit of Ko = 17 mag, the total microlensing rate is 3 x 10-3 yr-1. The rate of events with durations ≥ 1 yr is I x 10-3 yr-1. The median value of the peak amplification for short events is AK ~ 0.75 mag above the detection threshold and is only weakly dependent o