Difference image analysis of the OGLE-II bulge data. II. Microlensing events

We present a sample of microlensing events discovered in the Difference Ima ge Analysis (DIA) of the OGLE-II images collected during three observing se asons, 1997-1999. 4424 light curves pass our criteria on the presence of a brightening episode on top of a constant baseline. Among those, 512 candida te microlensing events were selected visually. We designed an automated pro cedure, which unambiguously selects up to 237 best events. Including eight candidate events recovered by other means, a total of 520 light curves are presented in this work. In addition to microlensing events, the larger sample contains certain type s of transients, but is also strongly contaminated by artifacts. All 4424 l ight curves in the weakly filtered group are available electronically, with the intent of showing the gray zone between microlensing events and variab le stars, as well as artifacts, to some extent inevitable in massive data r eductions. We welcome suggestions for improving the selection process befor e the full analysis of complete four seasons of the OGLE-H bulge data. Sele ction criteria for binary events can also be investigated with our extended sample.