2019/05/31 by Sunao Sugiyama, Toshiki Kurita, Masahiro Takada · 1 citation
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.1093/mnras/staa407
Accepted for publication in MNRAS; 10 pages, 8 figures. Typos are corrected. Fig.4 is newly added
arxiv created 2020/03/30 · arxiv updated 2020/03/31
Microlensing of stars, e.g. in the Galactic bulge and Andromeda galaxy (M31), is among the most robust, powerful method to constrain primordial black holes (PBHs) that are a viable candidate of dark matter. If PBHs are in the mass range M\rm PBH \lower.5ex\hbox \buildrel < \over ∼ 10-10M_\odot, its Schwarzschild radius (r\rm Sch) becomes comparable with or shorter than optical wavelength (λ) used in a microlensing search, and in this regime the wave optics effect on microlensing needs to be taken into account. For a lensing PBH with mass satisfying r\rm Sch∼ λ, it causes a characteristic oscillatory feature in the microlensing light curve, and it will give a smoking gun evidence of PBH if detected, because any astrophysical object cannot have such a tiny Schwarzschild radius. Even in a statistical study, e.g. constraining the abundance of PBHs from a systematic search of microlensing events for a sample of many source stars, the wave effect needs to be taken into account. We examine the impact of wave effect on the PBH constraints obtained from the r-band (6210Å) monitoring observation of M31 stars in Niikura et al. (2019), and find that a finite source size effect is dominant over the wave effect for PBHs in the mass range M\rm PBH≃[10-11,10-10]M_\odot. We also discuss that, if a denser-cadence (10~sec), g-band monitoring observation for a sample of white dwarfs over a year timescale is available, it would allow one to explore the wave optics effect on microlensing light curve, if it occurs, or improve the PBH constraints in M\rm PBH\lower.5ex\hbox \buildrel < \over ∼ 10-11M_\odot even from a null detection.