Statistical properties of gamma-ray burst polarization

Kenji Toma, Takanori Sakamoto, Bing Zhang, Joanne E. Hill, Mark L. McConnell, Peter F. Bloser, Ryo Yamazaki, Kunihito Ioka, Takashi Nakamura

Research output: Contribution to journalArticlepeer-review

92 Citations (Scopus)

Abstract

The emission mechanism and the origin and structure of magnetic fields in gamma-ray burst (GRB) jets are among the most important open questions concerning the nature of the central engine of GRBs. In spite of extensive observational efforts, these questions remain to be answered and are difficult or even impossible to infer with the spectral and light-curve information currently collected. Polarization measurements will lead to unambiguous answers to several of these questions. Recent developments in X-ray and γ-ray polarimetry techniques have demonstrated a significant increase in sensitivity, enabling several new mission concepts, e.g., Polarimeters for Energetic Transients (POET), providing wide field of view and broadband polarimetry measurements. If launched, missions of this kind would finally provide definitive measurements of GRB polarizations. We perform Monte Carlo simulations to derive the distribution of GRB polarizations in three emission models; the synchrotron model with a globally ordered magnetic field (SO model), the synchrotron model with a small-scale random magnetic field (SR model), and the Compton drag model (CD model). The results show that POET, or other polarimeters with similar capabilities, can constrain the GRB emission models by using the statistical properties of GRB polarizations. In particular, the ratio of the number of GRBs for which the polarization degrees can be measured to the number of GRBs that are detected (Nm /Nd ) and the distributions of the polarization degrees (Π) can be used as the criteria. If Nm /Nd > 30% and Π is clustered between 0.2 and 0.7, the SO model will be favored. If, instead, Nm /Nd < 15%, then the SR or CD model will be favored. If several events with Π>0.8 are observed, then the CD model will be favored.

Original languageEnglish
Pages (from-to)1042-1053
Number of pages12
JournalAstrophysical Journal
Volume698
Issue number2
DOIs
Publication statusPublished - 2009

Keywords

  • Gamma rays: bursts
  • Magnetic fields
  • Polarization
  • Radiation mechanisms: non-thermal

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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