GRB 140206A: the most distant polarized Gamma-Ray Burst

TL;DR

This paper reports the most distant measurement of gamma-ray polarization in a GRB, providing insights into the emission mechanisms and setting stringent limits on Lorentz Invariance Violation using multi-instrument observations.

Contribution

It presents the first polarization measurement of GRB 140206A at z=2.739, and constrains Lorentz Invariance Violation with the deepest limit to date from a cosmological source.

Findings

Polarization level >28% at 90% confidence for the second peak.

Distance of GRB 140206A measured at z=2.739.

Stringent limit on Lorentz Invariance Violation (ξ < 1x10^-16).

Abstract

The nature of the prompt gamma-ray emission of Gamma-Ray Bursts (GRBs) is still far from being completely elucidated. The measure of linear polarization is a powerful tool that can be used to put further constraints on the content and magnetization of the GRB relativistic outflows, as well as on the radiation processes at work. To date only a handful of polarization measurements are available for the prompt emission of GRBs. Here we present the analysis of the prompt emission of GRB 140206A, obtained with INTEGRAL/IBIS, Swift/BAT, and Fermi/GBM. Using INTEGRAL/IBIS as a Compton polarimeter we were able to constrain the linear polarization level of the second peak of this GRB as being larger than 28% at 90% c.l. We also present the GRB afterglow optical spectroscopy obtained at the Telescopio Nazionale Galileo (TNG), which allowed us the measure the distance of this GRB, z=2.739. This distance value together with the polarization measure obtained with IBIS, allowed us to derive the deepest and most reliable limit to date (xi <1x10-16) on the possibility of Lorentz Invariance Violation, measured through the vacuum birefringence effect on a cosmological source.