Testing Einstein's Equivalence Principle with Short Gamma-ray Bursts

TL;DR

This study tests Einstein's Equivalence Principle using the spectra of 20 short gamma-ray bursts, providing the most precise constraints to date on potential violations of the principle.

Contribution

It introduces a novel method utilizing continuous spectra of GRBs to improve the accuracy of EEP tests compared to previous photon-based approaches.

Findings

The strictest constraint on EEP violation is $|eta(150~{ m keV})-eta(15~{ m keV})|<5.59\times 10^{-10}$.

The constraints are 10 to 100 times tighter than previous results.

Using continuous spectra enhances the statistical significance of the tests.

Abstract

Einstein's equivalence principle (EEP) can be tested by the time delay between photons with different energies passing through a gravitational field. As one of the most energetic explosions in the Universe, gamma-ray bursts (GRBs) provide an effective tool to test the accuracy of EEP. In this paper, we use the continuous spectra of 20 short GRBs detected by the Swift/BAT to test the validity of EEP. Taking the duration of GRBs as the upper limit of the time delay induced by EEP violation (assuming that the high energy photons arrive later than the low energy photons), the difference of the parameterized post-Newtonian parameter is constrained with high accuracy. The strictest constraint, $|\gamma(150~{\rm keV})-\gamma(15~{\rm keV})|<5.59\times 10^{-10}$ from GRB 150101B, is about $1\sim 2$ orders of magnitude tighter than previous constraints. Moreover, our result is more statistically significant than previous results because we use the continuous spectra instead of isolated photons.