Optical Gravitational Lensing Experiment OGLE‐1999‐BUL‐32: the longest ever microlensing event – evidence for a stellar mass black hole?

  title={Optical Gravitational Lensing Experiment OGLE‐1999‐BUL‐32: the longest ever microlensing event – evidence for a stellar mass black hole?},
  author={Shude Mao and Martin C. Smith and Przemyslaw Remigiusz Wozniak and Andrzej Udalski and Marcin Kubiak and Grzegorz Pietrzyński and Igor Soszyński and K. Żebruń},
  journal={Monthly Notices of the Royal Astronomical Society},
We describe the discovery of the longest microlensing event ever observed, OGLE-1999-BUL-32, also independently identified by the MACHO collaboration as MACHO-99-BLG-22. This unique event has an Einstein radius crossing time of 640 d. The high-quality data obtained with difference image analysis shows a small but significant parallax signature. This parallax effect allows one to determine the Einstein radius projected on to the observer plane as r E 29.1 au. The transverse velocity projected on… 

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