HST Imaging of MEGA Microlensing Candidates in M31

Abstract

We investigate $HST$/ACS and WFPC2 images at the positions of five candidate microlensing events from a large survey of variability in M31 (MEGA). Three closely match unresolved sources, and two produce only flux upper limits. All are confined to regions of the color-magnitude diagram where stellar variability is unlikely to be easily confused with microlensing. Red variable stars cannot explain these events (although background supernova are possible for two). If these lenses arise in M31's halo, they are due to masses $0.15<m/M_{\odot }<0.49$ (95% certainty, for a $\delta$-function mass distribution), brown dwarfs for disk lenses, and stellar masses for bulge lenses.

Accepted for publication in ApJL. Higher resolution version available at http://www.astro.columbia.edu/~patrick/hst/hst_ml.pdf

References in corpus (6)

• RR Lyrae Stars in the Andromeda Halo from Deep Imaging with the Advanced Camera for Surveys
• The Wendelstein Calar Alto Pixellensing Project(WeCAPP): First MACHO Candidates
• First Microlensing Events From The MEGA Survey Of M31
• Evidence of Halo Microlensing in M31
• A Candidate M31/M32 Intergalactic Microlensing Event
• First microlensing candidate towards M31 from the Nainital Microlensing Survey

Cited by in corpus (4)

• PAndromeda - first results from the high-cadence monitoring of M31 with Pan-STARRS 1
• M31 pixel lensing event OAB-N2: a study of the lens proper motion
• Pixel lensing: Microlensing towards M31
• Planetary Nebula Velocities in the Disk and Bulge of M31