Nonlinear particle acceleration and thermal particles in GRB afterglows

Abstract

The standard model for GRB afterglow emission treats the accelerated electron population as a simple power law, $N(E)\propto E^{-p}$ for $p\gtrsim 2$. However, in standard Fermi shock acceleration a substantial fraction of the swept-up particles do not enter the acceleration process at all. Additionally, if acceleration is efficient then the nonlinear backreaction of accelerated particles on the shock structure modifies the shape of the non-thermal tail of the particle spectra. Both of these modifications to the standard synchrotron afterglow impact the luminosity, spectra, and temporal variation of the afterglow. To examine the effects of including thermal particles and nonlinear particle acceleration on afterglow emission, we follow a hydrodynamical model for an afterglow jet and simulate acceleration at numerous points during the evolution. When thermal particles are included, we find that the electron population is at no time well-fitted by a single power law, though the highest-energy electrons are; if the acceleration is efficient, then the power law region is even smaller. Our model predicts hard-soft-hard spectral evolution at X-ray energies, as well as an uncoupled X-ray and optical light curve. Additionally, we show that including emission from thermal particles has drastic effects (factors of 100 and 30, respectively) on the observed flux at optical and GeV energies. This enhancement of GeV emission makes afterglow detections by future $\gamma$-ray observatories, such as CTA, very likely.

18 pages, 9 figures

References in corpus (17)

• The Physics of Gamma-Ray Bursts and Relativistic Jets
• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge
• A comprehensive analysis of Swift/XRT data: I. Apparent spectral evolution of GRB X-ray tails
• Observations of the Naked-Eye GRB 080319B: Implications of Nature's Brightest Explosion
• Blazar Gamma-Rays, Shock Acceleration, and the Extragalactic Background Light
• Gamma Ray Bursts Are Observed Off-Axis
• Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow
• Extragalactic Zeeman Detections in OH Megamasers
• Multiwavelength analysis of the intriguing GRB 061126: the reverse shock scenario and magnetization
• Magnetic field amplification in nonlinear diffusive shock acceleration including resonant and non-resonant cosmic-ray driven instabilities
• Phenomenology of Reverse-Shock Emission in the Optical Afterglows of Gamma Ray Bursts
• Particle Transport in intense small scale magnetic turbulence with a mean field
• Shock Corrugation by Rayleigh-Taylor Instability in GRB Afterglow Jets
• Electron and Ion Acceleration in Relativistic Shocks with Applications to GRB Afterglows
• Simulations of gamma-ray burst afterglows with a relativistic kinetic code

Cited by in corpus (8)

• A very-high-energy component deep in the Gamma-ray Burst afterglow
• The Gamma-ray Bursts fundamental plane correlation as a cosmological tool
• Cosmic ray production in supernovae
• Gamma-Ray Bursts, Quasars, Baryonic Acoustic Oscillations, and Supernovae Ia: new statistical insights and cosmological constraints
• On the Existence of the Plateau Emission in High-Energy Gamma-Ray Burst LightCurves observed byFermi-LAT
• Closure relations during the plateau emission of Swift GRBs and the fundamental plane
• Origin of sub-TeV afterglow emission from gamma-ray bursts GRB 190114C and GRB 180720B
• 1000 days of lowest frequency emission from the low-luminosity GRB 171205A