Quantum gravity may cause modification of the dispersion relation for photons at high energies. It has recently been suggested that certain quantum gravity models may lead to a first order correction to the dispersion relation which can be parameterized as , where is the magnitude of the travel time difference between two photons whose energies differ by and that have traveled a distance L, and is the energy scale of the dispersion effects (Amelino-Camelia et al. 1998). To probe dispersion effects at high energy scales, accurate relative timing of nearly simultaneously produced photons of different energies which have traveled long distances is required. Use of sub-millisecond time structure of the keV photon flux of gamma-ray bursts at cosmological distances (Amelino-Camelia et al. 1998; Schaefer 1998) and use of several minute time structure in TeV flares from AGN (Biller et al. 1998) have been suggested. Here, we show that sub-millisecond timing of GeV emission from gamma-ray pulsars may also place useful constraints on the dispersion relation for photons at high energies.
Below, we use existing gamma-ray data to determine the accuracy with which high energy pulsar emission can be timed and to place bounds on the energy scale for quantum gravity corrections to the speed of light. We then discuss how this limit might be improved by pulsar observations at higher energies in the near future.
© European Southern Observatory (ESO) 1999
Online publication: April 19, 1999