Early polarization observations of the optical emission of gamma-ray bursts: GRB150301B and GRB150413A

TL;DR

This paper presents the earliest optical polarization measurements of gamma-ray bursts, revealing polarization levels in one burst and none in another, providing insights into the prompt optical emission stages.

Contribution

It reports the first early polarization observations of GRBs and presents high-quality light curves during their non-monotonic evolution stages.

Findings

Minimum polarization of 8% for GRB150301B

No polarization detected for GRB150413A

Discovery of optical counterpart for GRB150413A

Abstract

We report early optical linear polarization observations of two gamma-ray bursts made with the MASTER robotic telescope network. We found the minimum polar- ization for GRB150301B to be 8% at the beginning of the initial stage, whereas we detected no polarization for GRB150413A either at the rising branch or after the burst reached the power-law afterglow stage. This is the earliest measurement of the polarization (in cosmological rest frame) of gamma-ray bursts. The primary intent of the paper is to discover optical emission and publish extremely rare (unique) high- quality light curves of the prompt optical emission of gamma-ray bursts during the non-monotonic stage of their evolution. We report that our team has discovered the optical counterpart of one of the bursts, GRB150413A.