Optical Microlensing by Primordial Black Holes with IACTs

Abstract

Primordial black holes (PBHs), hypothesized to be the result of density fluctuations during the early universe, are candidates for dark matter. When microlensing background stars, they cause a transient apparent enhancement of the flux. Measuring these signals with optical telescopes is a powerful method to constrain the PBH abundance in the range of $10^{-10}{M}_{\odot }$ to $10^1{M}_{\odot }$. Especially for galactic stars, the finiteness of the sources needs to be taken into account. For low PBH masses (in this work $\lesssim 10^{-8}{M}_{\odot }$) the average duration of the detectable event decreases with the mass $⟨t_e⟩\propto M_{\mathrm{PBH}}$. For $M_{\mathrm{PBH}}\approx 10^{-11}{M}_{\odot }$ we find $⟨t_e⟩\lesssim 1\mathrm{s}$. For this reason, fast sampling detectors may be required as they could enable the detection of low mass PBHs. Current limits are set with sampling speeds of 2 minutes to 24 hours in the optical regime. Ground-based Imaging Atmospheric Cherenkov telescopes (IACTs) are optimized to detect the $\sim$ns long optical Cherenkov signals induced by atmospheric air showers. As shown recently, the very-large mirror area of these instruments provides very high signal to noise ratio for fast optical transients ($\ll 1$s) such as asteroid occultations. We investigate whether optical observations by IACTs can contribute to extending microlensing limits to the unconstrained mass range $M_{\mathrm{PBH}}<10^{-10}{M}_{\odot }$. We discuss the limiting factors to perform these searches for each telescope type. We calculate the rate of expected detectable microlensing events in the relevant mass range for the current and next-generation IACTs considering realistic source parameters.

8 pages, 3 figures, Proceedings of the 37th International Cosmic Ray Conference (ICRC 2021), Berlin, Germany

References in corpus (3)

• Limits on the Macho Content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
• Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events
• Direct measurement of stellar angular diameters by the VERITAS Cherenkov Telescopes

Cited by in corpus (2)

• Dark Matter and Fundamental Physics Searches with IACTs
• The Maximal Gravitational Wave Signal from Asteroid-Mass Primordial Black Hole Mergers At Resonant Microwave Cavities