Primordial Black Hole signatures from femtolensing and spectral fringe of Gamma Ray Bursts

TL;DR

This study investigates femtolensing effects in gamma-ray bursts to constrain primordial black hole dark matter, using wave optics formalism and Swift XRT data, and sets upper bounds on PBH abundance.

Contribution

It applies wave optics analysis to GRB spectral data to search for femtolensing signatures and derive constraints on primordial black hole dark matter.

Findings

Some GRB spectra show spectral fringes indicative of femtolensing.

Most spectral fits do not improve with PBH lensing, allowing upper bounds to be set.

Robust constraints require GRB sizes smaller than 5×10^7 m for certain PBH masses.

Abstract

Femtolensing of gamma-ray bursts (GRBs) is vastly studied to constrain primordial black holes lighter than $10^{-13}$ solar mass and may close the window for PBH dark matter. In this case, wave optics formalism is required and carefully implemented in our analysis. Incorporating the GRB observational data from Swift XRT, we perform the statistical analysis of PBH lensing, comparing it with the null hypothesis where the BAND model is used to parametrize the GRB spectrum. We found a few GRB data manifest the spectral fringe which characterizes the feature of femtolensing by PBHs, and the analysis shows moderate statistical preference in terms of goodness of fit. Conversely, since most of the fits to GRB spectral data do not improve with PBH lensing, we utilize this to obtain an upper bound on the PBH fractional abundance with respect to dark matter. However, the robust constraint cannot be achieved, unless the size of GRBs is smaller than $5\times 10^7$ m for PBH mass around $5\times 10^{-15}$ solar mass.