Strong Lensing of Gamma Ray Bursts as a Probe of Compact Dark Matter

TL;DR

This paper proposes using strong gravitational lensing of gamma-ray bursts to detect or constrain compact dark matter objects in the 10 to 1000 solar mass range, analyzing existing data and forecasting future observational capabilities.

Contribution

It introduces a novel method to probe massive compact dark matter via GRB lensing and assesses current and future observational constraints.

Findings

Current data is noise limited for detection.

Localization-based masking improves sensitivity.

Future observatories can probe dark matter fraction down to 1%.

Abstract

Compact dark matter has been efficiently constrained in the M <~ 10 M_sun mass range by null searches for microlensing of stars in nearby galaxies. Here we propose to probe the mass range M >~ 10 M_sun by seeking echoes in gamma-ray-burst light curves induced by strong lensing. We show that strong gravitational lensing of gamma ray bursts (GRBs) by massive compact halo objects (MACHOs) generates superimposed GRB images with a characteristic time delay of >~ 1 ms for M >~ 10 M_sun. Using dedicated simulations to capture the relevant phenomenology of the GRB prompt emission, we calculate the signal-to-noise ratio required to detect GRB lensing events as a function of the flux ratio and time delay between the lensed images. We then analyze existing data from the Fermi/GBM and Swift/BAT instruments to assess their constraining power on the compact dark matter fraction f_DM. We find that this data is noise limited, and therefore localization-based masking of background photons is a key ingredient. Future observatories with better sensitivity will be able to probe down to the f_ DM >~ 1% level across the 10 M_sun <~ M <~ 1000 M_sun mass range.