Constraining Primordial Black Hole Dark Matter with CHIME Fast Radio Bursts

Abstract

Strong lensing of Fast Radio Bursts (FBRs) has been proposed as a relatively clean probe of primordial black hole (PBH) dark matter. Recently, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) published a first catalog of 536 FRBs, 62 of which are from repeating sources. In light of this new data, we re-examine the prospects to constrain the abundance of PBHs via FRBs. Extending previous forecasts, we calculate a PBH dark matter bound using the intrinsic burst width and a calibrated flux-ratio threshold per FRB. In addition, we take into account the uncertainty in the relation between the FRB dispersion measure and source redshift. We outline an algorithm to detect lensed FRBs and a method to simulate its performance on real data and set a flux-ratio threshold for each event, which we use to infer realistic forecasts. We then attempt to extract a preliminary bound using the publicly available CHIME data. Unfortunately, both instrumental noise and the provided ∼ 1 ms time-resolution of the public data hinder this effort. We identify one candidate event where a double burst could be explained via strong lensing by a O(10 M )-mass PBH, which will require follow-up study at higher time resolution to either confirm or discard. We show that with a few times the size of the first catalog-sampled at the full instrumental timeresolution so that candidates can be efficiently scrutinized-CHIME will be able to find strong evidence for or robustly rule out PBHs with mass above ∼ 10 M as the dark matter. Finally, we demonstrate that stacking repeating FRBs can improve the constraints, especially for lower masses.

Snowmass2021 Cosmic Frontier White Paper: Dark Matter Physics from Halo Measurements

“…As a consequence, a fiducial observation of 10 4 FRBs (as expected from CHIME) can test any fraction of DM in compact objects down to 1% of the total DM abundance. Direct microlensing (i.e., searching for a lensed FRB echo) can detect lenses with masses M lens 10 M [594] (see [614,615] for current searches), whereas "femtolensing" (where the time delay is shorter and fringes appear in the FRB spectra) can test the range M lens ∼ 10 −4 − 10 M [595]. Searching for fuzzier lenses (for instance NFW halos) requires more FRBs, as the optical depth is reduced if the mass of the lens is not entirely contained within its Einstein radius.…”

Constraining Primordial Black Holes using Fast Radio Burst Gravitational-Lens Interferometry with CHIME/FRB

“…To be conservative, we take only the brightest burst from each repeating FRB source for the best measurement of ε 2 (τ ) along that sightline. Combining information from repeat bursts is in principle possible by e.g., stacking the measured ACF over many bursts [60]. However, at the nanosecond time resolution of our search, changes in the lensing delay over time (a so-called "delay-rate") must be taken into account to not wash out the signal from the stacking procedure.…”