# Polarimetry and Photometry of Gamma-Ray Bursts with RINGO2

## TL;DR

This paper presents a catalog of early-time optical photometry and polarimetry of gamma-ray burst afterglows observed with RINGO2, confirming significant polarization in some cases and linking it to reverse-shock emission.

## Contribution

It provides the first comprehensive early-time polarimetric catalog of GRB afterglows and demonstrates the connection between polarization detection and reverse-shock signatures.

## Key findings

- Confirmed significant polarization in GRB 110205A and 120308A.
- Detected 6% polarization in GRB 101112A.
- Linked early-time polarization to reverse-shock emission signatures.

## Abstract

We present a catalog of early-time (~10^2-10^4s) photometry and polarimetry of all Gamma-Ray Burst (GRB) optical afterglows observed with RINGO2 imaging polarimeter on the Liverpool Telescope. For the 19 optical afterglows observed, the following 9 were bright enough to perform photometry and attempt polarimetry: GRB 100805A, GRB 101112A, GRB 110205A, GRB 110726A, GRB 120119A, GRB 120308A, GRB 120311A, GRB 120326A and GRB 120327A. We present multi-wavelength light curves for these 9 GRBs, together with estimates of their optical polarization degrees and/or limits. We carry out a thorough investigation of detection probabilities, instrumental properties and systematics. Using two independent methods, we confirm previous reports of significant polarization in GRB 110205A and 120308A, and report new detection of $P=6^{+3}_{-2}\%$ in GRB101112A. We discuss the results for the sample in the context of the reverse and forward shock afterglow scenario, and show that GRBs with detectable optical polarization at early time have clearly identifiable signatures of reverse-shock emission in their optical light curves. This supports the idea that GRB ejecta contain large-scale magnetic fields and highlights the importance of rapid-response polarimetry.