Light speed variation from GRB 221009A

Abstract

It is postulated in Einstein’s relativity that the speed of light in vacuum is a constant for all observers. However, the effect of quantum gravity could bring an energy dependence of light speed, and a series of studies on high-energy photon events from gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) suggest a light speed variation with E LV = 3.6 × 1017 GeV or a bound E LV ≥ 3.6 × 1017 GeV. From the newly observed gamma-ray burst GRB 221009A, we find that a 99.3 GeV photon detected by Fermi-Large Area Telescope (LAT) is coincident with the sharp spike in the light curves detected by both Fermi-Gamma-ray Burst Monitor (GBM) and HEBS under the above scenario of light speed variation, suggesting an option that this high-energy photon was emitted at the same time as a sharp spike of low-energy photon emission at the GRB source. Thus this highest energy photon event detected by Fermi-LAT during the prompt emission of GRBs might be considered as an optional signal for the linear form modification of light speed in cosmological space.