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Investigating polarization signatures from GRB models

Pieter vd Merwe, Markus Böttcher

Abstract

There is still much debate around the inner workings of the GRB prompt emission phase with many questions still left unanswered. Polarization signatures offer a promising new avenue to discriminate between the various GRB prompt emission models. The aim of this study is to estimate energy and time resolved polarization signatures resulting from Inverse Compton (IC) scattering for two specific GRB prompt emission models, namely the backscatter-dominated cork model by \citet{Vyas2} and a Compton drag model by \citet{Lazzati2}. In order to achieve this we apply an IC polarization Monte Carlo (MC) algorithm to those two GRB models in order to estimate the expected polarization signatures. For the backscatter-dominated cork model we find polarization signatures below $\sim 10$~\%, likely below the detection limits of current or near-future X-ray and $γ$-ray polarimeters. Our results for the Compton drag model indicates polarization results consistent with that found by \citet{Lazzati3}. Furthermore, we find some energy and time dependence of the estimated polarization, particularly for the polarization angle.

Investigating polarization signatures from GRB models

Abstract

There is still much debate around the inner workings of the GRB prompt emission phase with many questions still left unanswered. Polarization signatures offer a promising new avenue to discriminate between the various GRB prompt emission models. The aim of this study is to estimate energy and time resolved polarization signatures resulting from Inverse Compton (IC) scattering for two specific GRB prompt emission models, namely the backscatter-dominated cork model by \citet{Vyas2} and a Compton drag model by \citet{Lazzati2}. In order to achieve this we apply an IC polarization Monte Carlo (MC) algorithm to those two GRB models in order to estimate the expected polarization signatures. For the backscatter-dominated cork model we find polarization signatures below ~\%, likely below the detection limits of current or near-future X-ray and -ray polarimeters. Our results for the Compton drag model indicates polarization results consistent with that found by \citet{Lazzati3}. Furthermore, we find some energy and time dependence of the estimated polarization, particularly for the polarization angle.
Paper Structure (15 sections, 19 equations, 16 figures)

This paper contains 15 sections, 19 equations, 16 figures.

Table of Contents

  1. Introduction
  2. The Monte Carlo code developed to run on GPUs
  3. Overview
  4. Drawing electrons
  5. Simulating inverse Compton Scattering
  6. Parallelization of the code using Numba CUDA and Cupy
  7. Backscatter-dominated Cork Model
  8. Drawing the photons
  9. Applying the algorithm to the backscatter-dominated cork model
  10. Results
  11. Compton drag model
  12. Calculating initial conditions for the Compton drag model
  13. Applying the algorithm to the Compton drag model
  14. Results
  15. Conclusions

Figures (16)

  • Figure 1: Diagram showing the geometry of the backscatter-dominated cork model recreated from Vyas1. $\theta_{j}$ indicates the cork opening angle, with $r_{i}$ indicating the distance from the star center to the rear edge of the cork.
  • Figure 2: SED of the backscatter model for monoenergetic seed photons and viewing angles $\theta_{obs}=0.055$, $0.105$, $0.155$ and $0.305$. The dashed lines show the results obtained by Vyas1 for the same set of parameters.
  • Figure 3: SED of the backscatter model for monoenergetic seed photons and viewing angles $\theta_{obs}=0.055$, $0.105$, $0.155$ and $0.305$ resticted to number of scattering events $l$. The dashed lines show the total SED result obtained by Vyas1 for the same set of parameters.
  • Figure 4: Lightcurve of the backscatter model for monoenergetic seed photons and viewing angles $\theta_{obs}=0.055$, $0.105$, $0.155$ and $0.305$. The dashed lines show the theoretical temporal result derived by Vyas1 for the same set of parameters.
  • Figure 5: Polarization degree and angle as a function of energy for the backscatter model for monoenergetic seed photons and viewing angles $\theta_{obs}=0.055$, $0.105$, $0.155$ and $0.305$.
  • ...and 11 more figures