AAS 195th Meeting, January 2000
Session 37. Stellar Mass Black Holes
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[37.07] Gravitational Microlensing Parallax Events: Evidence for Isolated Black Hole Stellar Remnants and White Dwarf MACHOs

D.P. Bennett (Notre Dame), C. Alcock (LLNL), R.A. Allsman (ANUSF), D. Alves (STSCI), T.S. Axelrod (MSSSO), D. Becker (Washington), K.H. Cook (LLNL), A. Crouch (Monash), A.D. Drake (MSSSO), P.C. Fragile (Notre Dame), K.C. Freeman (MSSSO), M. Geha (LLNL), J. Gray (Monash), K. Griest (UCSD), B.R. Johnson (Minnesota), M.J. Lehner (Sheffield), S.L. Marshall (LLNL), B. Messenger (Monash), D. Minniti (P. Universidad Católica), C.A. Nelson (LLNL), B.A. Peterson (MSSSO), P. Popowski (LLNL), J.L. Quinn (Notre Dame), P.J. Quinn (ESO), S.H. Rhie (Notre Dame), P. Stetson (DAOb), C.W. Stubbs (Washington), W. Sutherland (Oxford), S. Thomson (Monash), A.B. Tomaney (Washington), T. Vandehei (UCSD), D. Welch (McMaster)

We present the analysis of microlensing parallax events discovered by the MACHO/GMAN and Microlensing Planet Search (MPS) Collaborations. We find two events towards the Galactic bulge which are likely to be caused by black hole lenses: MACHO-96-BLG-5 and MACHO-98-BLG-6. The microlensing parallax constraint on the lens masses and the observed upper limit on the lens brightness imply that these lenses are likely to be black holes. If so, they would be the first isolated black holes in the stellar mass range yet discovered. Our microlensing parallax analysis of Large Magellanic Could (LMC) microlensing events yields a single event, MACHO-LMC-22 which appears to have a significant parallax signal. The microlensing parallax analysis indicates that the lens does not reside in the Milky Way's thin disk or in the vicinity of the LMC. The parallax analysis suggests that the lens star must reside in the Milky Way's thick disk or dark halo. This lends support to recent suggestions that old, blue white dwarfs seen in the Hubble Deep Fields might be responsible for the excess microlensing signal seen toward the LMC.

This work was funded by the NSF, the NASA Origins Program and the DOE (through LLNL).

The author(s) of this abstract have provided an email address for comments about the abstract: bennett@nd.edu

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