The Nature of Parallax Microlensing Events Towards the Galactic Bulge

Abstract

Perhaps as many as 30 parallax microlensing events are known, thanks to the efforts of the MACHO, OGLE, EROS and MOA experiments monitoring the bulge. Using Galactic models, we construct mock catalogues of microlensing light curves towards the bulge, allowing for the uneven sampling and observational error bars of the OGLE-II experiment. The fraction of parallax events with delta chi^2 > 50 in the OGLE-II database is around ~1%, though higher fractions are reported by some other surveys. This is in accord with expectations from standard Galactic models. The fraction of parallax events depends strongly on the Einstein crossing time (t_E), being less than 5% at t_E = 50 days but rising to 50% at t_E > 1 yr. We find that the existence of parallax signatures is essentially controlled by the acceleration of the observer normalised to the projected Einstein radius on the observer plane divided by t_E^2. The properties of the parallax events - time-scales, projected velocities, source and lens locations - in our mock catalogues are analysed. Typically, ~38% of parallax events are caused by a disk star microlensing a bulge source, while \~33% are caused by a disk star microlensing a disk source (of these disk sources, one sixth are at a distance of 5 kpc or less). There is a significant shift in mean time-scale from 32 d for all events to ~130d for our parallax events. There are corresponding shifts for other parameters, such as the lens-source velocity projected onto the observer plane (~1110 km/s for all events versus ~80 km/s for parallax events) and the lens distance (6.7 kpc versus 3.7 kpc). We also assess the performance of parallax mass estimators and investigate whether our mock catalogue can reproduce events with features similar to a number of conjectured `black hole' lens candidates.

arXiv comment15 pages, 13 figures, MNRAS (in press)

References in corpus (42)

• The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems
• Real-Time Difference Imaging Analysis of MOA Galactic Bulge Observations During 2000
• Three Dimensional Structure of the Milky Way Disk
• Gravitational Microlensing in the Local Group
• Resolution of the MACHO-LMC-5 Puzzle: The Jerk-Parallax Microlens Degeneracy
• Modelling the Galactic Bar Using Red Clump Giants
• Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis
• Stellar Contribution to the Galactic Bulge Microlensing Optical Depth
• First microlens mass measurement: PLANET photometry of EROS BLG-2000-5
• The Initial Mass Function of the Galactic Bulge Down to ~0.15 Msun
• Cuspy Dark-Matter Haloes and the Galaxy
• Measuring the Remnant Mass Function of the Galactic Bulge
• Gravitational Microlensing Events Due to Stellar Mass Black Holes
• Acceleration and Parallax Effects in Gravitational Microlensing
• Gravitational Microlensing with the Space Interferometry Mission
• Optical Gravitational Lensing Experiment. OGLE-1999-BUL-32: the Longest Ever Microlensing Event -- Evidence for a Stellar Mass Black Hole?
• Binary Microlensing Events from the MACHO Project
• Statistics Of Microlensing Optical Depth
• Extinction Map of Baade's Window
• Bulge Microlensing Optical Depth from EROS 2 observations
• M Dwarfs from Hubble Space Telescope Star Counts. IV
• Astrometric Microlensing with the GAIA satellite
• OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star
• MOA 2003-BLG-37: A Bulge Jerk-Parallax Microlens Degeneracy
• The Point-Agape survey: 4 high signal-to-noise ratio microlensing candidates detected towards M31
• Resolving gravitational microlensing events with long-baseline optical interferometry. Prospects for the ESO Very Large Telescope Interferometer
• Mass Determination With Gravitational Microlensing
• Finding Black Holes with Microlensing
• The Mass of the MACHO-LMC-5 Lens Star
• UNIFICATION OF THE NEARBY AND PHOTOMETRIC STELLAR LUMINOSITY FUNCTIONS
• Optical Gravitational Lensing Experiment. OGLE 2000-BUL-43: A Spectacular Ongoing Parallax Microlensing Event. Difference Image Analysis
• Potential Direct Single-Star Mass Measurement
• Microlensing Maps for the Milky Way Galaxy
• Parallax Microlensing Events in the OGLE II Database Toward the Galactic Bulge
• Magnitude Offset between Lensed Stars and Observed Stars - a New Probe of the Structure of the Galactic Bar
• Optical Gravitational Lensing Experiment. OGLE-1999-BUL-19: The First Multi-Peak Parallax Event
• Parallax-Shifted Microlensing Events from Ground-Based Observations of the Galactic Bulge
• Constraining the Galactic Bar Parameters with Red Clump Giants
• Microlens Parallax Asymmetries Toward the LMC
• The Sagittarius dwarf galaxy as a microlensing target
• The OGLE-II event sc5_2859 -- An example of disk-disk microlensing
• Harmonizing the RR Lyrae and Clump Distance Scales - Stretching the Short Distance Scale to Intermediate Ranges?

Cited by in corpus (10)

• Black Hole, Neutron Star and White Dwarf Candidates from Microlensing with OGLE-III
• Systematic Analysis of 22 Microlensing Parallax Candidates
• Constraining the masses of microlensing black holes and the mass gap with Gaia DR2
• ExELS: an exoplanet legacy science proposal for the ESA Euclid mission I. Cold exoplanets
• Blending in Gravitational Microlensing Experiments: Source Confusion And Related Systematics
• First semi-empirical test of the white dwarf mass-radius relationship using a single white dwarf via astrometric microlensing
• A Reanalysis of Public Galactic Bulge Gravitational Microlensing Events from OGLE-III and IV
• Rapidly Rotating Lenses: Repeating features in the lightcurves of short period binary microlenses
• On the Possibility of Stellar Lenses in the Black Hole Candidate Microlensing Events MACHO-96-BLG-5 and MACHO-98-BLG-6
• Using microlensed quasars to probe the structure of the Milky Way