VVV Survey Microlensing Events in the Galactic Center Region

Abstract

We search for microlensing events in the highly reddened areas surrounding the Galactic center using the near-IR observations with the VISTA Variables in the V\'ia L\'actea Survey (VVV). We report the discovery of 182 new microlensing events, based on observations acquired between 2010 and 2015. We present the color-magnitude diagrams of the microlensing sources for the VVV tiles b332, b333, and b334, which were independently analyzed, and show good qualitative agreement among themselves. We detect an excess of microlensing events in the central tile b333 in comparison with the other two tiles, suggesting that the microlensing optical depth keeps rising all the way to the Galactic center. We derive the Einstein radius crossing time for all of the observed events. The observed event timescales range from $t_E = 5$ to $200$ days. The resulting timescale distribution shows a mean timescale of $=30.91$ days for the complete sample ($N = 182$ events), and $=29.93$ days if restricted only for the red clump (RC) giant sources ($N = 96$ RC events). There are 20 long timescale events ($t_E \geq 100$ days) that suggest the presence of massive lenses (black holes) or disk-disk event. This work demonstrates that the VVV Survey is a powerful tool to detect intermediate/long timescale microlensing events in highly reddened areas, and it enables a number of future applications, from analyzing individual events to computing the statistics for the inner Galactic mass and kinematic distributions, in aid of future ground- and space-based experiments.Comment: 8 pages, 4 figures, published on The Astrophysical Journal Letter