Temporal Evolution of Prompt GRB Polarization

Abstract

The dominant radiation mechanism that produces the prompt emission in gamma-ray bursts (GRBs) remains a major open question. Spectral information alone has proven insufficient in elucidating its nature. Time-resolved linear polarization has the potential to distinguish between popular emission mechanisms, e.g., synchrotron radiation from electrons with a power-law energy distribution or inverse Compton scattering of soft seed thermal photons, which can yield the typical GRB spectrum but produce different levels of polarization. Furthermore, it can be used to learn about the outflow's composition (i.e. whether it is kinetic-energy-dominated or Poynting-flux-dominated) and angular structure. For synchrotron emission it is a powerful probe of the magnetic field geometry. Here we consider synchrotron emission from a thin ultrarelativistic outflow, with bulk Lorentz factor $\Gamma (R)={\Gamma }_0(R/R_0{)}^{-m/2}\gg 1$, that radiates a Band-function spectrum in a single (multiple) pulse(s) over a range of radii, $R_0\le R\le R_0+\Delta R$. Pulse profiles and polarization evolution at a given energy are presented for a coasting ($m=0$) and accelerating ($m=-2/3$) thin spherical shell and for an off-axis top-hat jet with sharp as well as smooth edges in emissivity. Four different magnetic field configurations are considered, such as a locally ordered field coherent over angular scales ${\theta }_B\gtrsim 1/\Gamma$, a tangled field ($B_{\perp }$) in the plane transverse to the radial direction, an ordered field ($B_{\parallel }$) aligned in the radial direction, and a globally ordered toroidal field ($B_{\mathrm{tor}}$). All field configurations produce distinct polarization evolution with single (for $B_{\perp }$ and $B_{\parallel }$) and double (for $B_{\mathrm{tor}}$) $90^{\circ }$ changes in the polarization position angle.

20 pages, 11 figures; added two more panels to Fig. 6 and main points of paper to the summary section; Accepted to MNRAS

References in corpus (24)

• The Physics of Gamma-Ray Bursts and Relativistic Jets
• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
• Prompt GRB emission from gradual energy dissipation
• Prompt emission spectra from the photosphere of a GRB
• Relativistic magnetic reconnection in pair plasmas and its astrophysical applications
• Gamma-ray Burst 080319B: Evidence for Relativistic Turbulence, Not Internal Shocks
• Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow
• Black-hole jets without large-scale net magnetic flux
• A Turbulent Model of Gamma-Ray Burst Variability
• Detailed polarization measurements of the prompt emission of five Gamma-Ray Bursts
• Towards a Better Understanding of the GRB Phenomenon: a New Model for GRB Prompt Emission and its effects on the New Non-Thermal L${}_{\mathrm{i}}^{\mathrm{NT}}$-E${}_{\mathrm{peak},\mathrm{i}}^{\mathrm{rest},\mathrm{NT}}$ relation
• Detection of Low-energy Breaks in Gamma-Ray Burst Prompt Emission Spectra
• Evidence of two spectral breaks in the prompt emission of gamma ray bursts
• Low-energy Spectra of Gamma-ray Bursts from Cooling Electrons
• Constraining the magnetic field structure in collisionless relativistic shocks with a radio afterglow polarization upper limit in GW170817
• Spectral and Polarization Properties of Photospheric Emission From Stratified Jets
• Radiative striped wind model for gamma-ray bursts
• Photospheric Polarization Signatures From Long Gamma Ray Burst Simulations
• The Effect of Pair Cascades on the High-Energy Spectral Cutoff in Gamma-Ray Bursts
• Non-thermal Gamma-ray Emission from Delayed Pair Breakdown in a Magnetized and Photon-rich Outflow
• The Synchrotron Polarization in Decaying Magnetic Field in Gamma-Ray Bursts
• GRB Spectrum from Gradual Dissipation in a Magnetized Outflow
• 2D Relativistic MHD Simulations of the Kruskal-Schwarzschild Instability in a Relativistic Striped Wind