# GRB lensing parallax: Closing primordial black hole dark matter mass window

## TL;DR

This paper proposes using GRB lensing parallax observations with spatially separated detectors to explore the unconstrained mass range of primordial black hole dark matter, potentially closing existing gaps in detection.

## Contribution

It introduces a novel application of GRB lensing parallax to probe primordial black hole masses between 10^{-16} and 10^{-11} solar masses, which are difficult to detect with current methods.

## Key findings

- GRB lensing parallax can probe the lightest PBH DM mass range.
- Nearby star lensing can explore heavier PBH masses.
- The method leverages astrophysical separations around 1 AU to resolve lensing effects.

## Abstract

The primordial black hole (PBH) comprising full dark matter (DM) abundance is currently allowed if its mass lies between $10^{-16}M_{\odot} \lesssim M \lesssim 10^{-11} M_{\odot}$. This lightest mass range is hard to be probed by ongoing gravitational lensing observations. In this paper, we advocate that an old idea of the lensing parallax of Gamma-ray bursts (GRBs), observed simultaneously by spatially separated detectors, can probe the unconstrained mass range; and that of nearby stars can probe a heavier mass range. In addition to various good properties of GRBs, astrophysical separations achievable around us --- $r_\oplus \text{--}$ AU --- is just large enough to resolve the GRB lensing by lightest PBH DM.