Volume 644, December 2020
|Number of page(s)||37|
|Section||Catalogs and data|
|Published online||10 December 2020|
The POLAR gamma-ray burst polarization catalog
Department of Nuclear and Particle Physics, University of Geneva, 24 quai Ernest-Ansermet, 1205 Geneva, Switzerland
2 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
3 University of Geneva, Geneva Observatory, ISDC, 16, Chemin d’Ecogia, 1290 Versoix, Switzerland
4 Paul Scherrer Institut, 5232 Villigen, Switzerland
5 Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, PR China
6 University of Chinese Academy of Sciences, Beijing 100049, PR China
7 National Centre for Nuclear Research, ul. A. Soltana 7, 05-400 Otwock, Swierk, Poland
8 Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland
Accepted: 14 September 2020
Context. Despite over 50 years of research, many open questions remain about the origin and nature of gamma-ray bursts (GRBs). Linear polarization measurements of the prompt emission of these extreme phenomena have long been thought to be key to answering a range of these questions. The POLAR detector was designed to produce the first set of detailed and reliable linear polarization measurements in the 50 − 500 keV energy range. During late 2016 and early 2017, POLAR detected a total of 55 GRBs. The analysis results of 5 of these GRBs have been reported, and were found to be consistent with a low or unpolarized flux. However, previous reports by other collaborations found high levels of linear polarization, including some as high as 90%.
Aims. We study the linear polarization for the 14 GRBs observed by POLAR for which statistically robust inferences are possible. Additionally, time-resolved polarization studies are performed on GRBs with sufficient apparent flux.
Methods. A publicly available polarization analysis tool, developed within the Multi-Mission Maximum Likelihood framework (3ML), was used to produce statistically robust results. The method allows spectral and polarimetric data from POLAR to be combined with spectral data from the Fermi Gamma-ray Burst Monitor (Fermi-GBM) and the Neil Gehrels Swift Observatory to jointly model the spectral and polarimetric parameters.
Results. The time-integrated analysis finds all results to be compatible with low or zero polarization with the caveat that, when time-resolved analysis is possible within individual pulses, we observe moderate linear polarization with a rapidly changing polarization angle. Therefore, time-integrated polarization results, while pointing to lower polarization, are potentially an artifact of summing over the changing polarization signal and thus washing out the true moderate polarization. We therefore caution against overinterpretation of any time-integrated results inferred herein and encourage the community to wait for more detailed polarization measurements from forthcoming missions such as POLAR-2 and LEAP.
Key words: polarization / methods: data analysis / instrumentation: polarimeters / catalogs / gamma-ray burst: general
© ESO 2020
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.