Limits on quantum gravity effects from Swift short gamma-ray bursts

¹ Laboratoire Univers et Particules de Montpellier, Université de Montpellier, CNRS/IN2P3, 34160 Montpellier, France
e-mail: bernardini@lupm.in2p3.fr
² INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
³ Université de Toulouse, UPS-OMP, IRAP, 31042 Toulouse, France
⁴ CNRS IRAP, 14 avenue Édouard Belin, 31400 Toulouse, France
⁵ INAF–IASF Milano, via E. Bassini 15, 20133 Milano, Italy

Received: 7 June 2017
Accepted: 15 October 2017

Abstract

The delay in arrival times between high and low energy photons from cosmic sources can be used to test the violation of the Lorentz invariance (LIV), predicted by some quantum gravity theories, and to constrain its characteristic energy scale E_QG that is of the order of the Planck energy. Gamma-ray bursts (GRBs) and blazars are ideal for this purpose thanks to their broad spectral energy distribution and cosmological distances: at first order approximation, the constraints on E_QG are proportional to the photon energy separation and the distance of the source. However, the LIV tiny contribution to the total time delay can be dominated by intrinsic delays related to the physics of the sources: long GRBs typically show a delay between high and low energy photons related to their spectral evolution (spectral lag). Short GRBs have null intrinsic spectral lags and are therefore an ideal tool to measure any LIV effect. We considered a sample of 15 short GRBs with known redshift observed by Swift and we estimate a limit on E_QG ≳ 1.5 × 10¹⁶ GeV. Our estimate represents an improvement with respect to the limit obtained with a larger (double) sample of long GRBs and is more robust than the estimates on single events because it accounts for the intrinsic delay in a statistical sense.