Optical Gravitational Lensing Experiment OGLE-1999-BUL-32: the longest ever microlensing event – evidence for a stellar mass black hole? |
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| Authors: | Shude Mao Martin C Smith P Wo&#;niak A Udalski M Szyma&#;ski M Kubiak G Pietrzy&#;ski I Soszy&#;ski K &#;ebru&#; |
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| Institution: | 1University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL;2Princeton University Observatory, Princeton, NJ 08544-1001, USA;3Los Alamos National Laboratory, MS D436, Los Alamos, NM 87545, USA;4Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland;5Universidad de Concepción, Departamento de Fisica, Casilla 160–C, Concepción, Chile |
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| Abstract: | 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  . The transverse velocity projected on to the observer plane is about 79 km s?1. We argue that the lens is likely to have a mass of at least a few solar masses, i.e. it could be a stellar black hole. The black hole hypothesis can be tested using the astrometric microlensing signature with the soon-to-be installed Advanced Camera for Surveys on board the Hubble Space Telescope . Deep X-ray and radio images may also be useful for revealing the nature of the object. |
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| Keywords: | black hole physics gravitational lensing Galaxy: bulge Galaxy: centre |
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