Gravitational Microlensing Events Due to Stellar Mass Black Holes

Preprint
Publisher Website
Google Scholar
  • 26 September 2001
Abstract
We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a seven year survey of the Galactic bulge. We find six events that exhibit very strong microlensing parallax signals due, in part to accurate photometric data from the GMAN and MPS collaborations. The microlensing parallax fit parameters are used in a likelihood analysis, which is able to estimate the distance and masses of the lens objects based upon a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of five of the six lenses are > 1 Msun which suggests that a substantial fraction of the Galactic lenses are massive stellar remnants. The lenses for events MACHO-96-BLG-5 and MACHO-98-BLG-6 are the most massive, with mass estimates of M/Msun = 6 +10/-3 and M/Msun = 6 +7/-3, respectively. The observed upper limits on the absolute brightness of these lenses are >~ 1 Lsun, so both lenses are black hole candidates. We consider the possibility that the source stars for some of these six events may lie in the foreground Galactic disk or in the Sagittarius (SGR) Dwarf Galaxy behind the bulge, but we find that bulge sources are likely to dominate our microlensing parallax event sample. Future HST observations of these events can either confirm the black hole lens hypothesis or detect the lens stars and provide a direct measurement of their masses. Future observations of similar events by SIM or the Keck or VLTI interferometers (astro-ph/0108178) will allow direct measurements of the lens masses for stellar remnant lenses as well.

This publication has 0 references indexed in Scilit: