Dissecting the Energy Budget of a Gamma-Ray Burst Fireball

Abstract

The jet composition and radiative efficiency of GRBs are poorly constrained from the data. If the jet composition is matter-dominated (i.e. a fireball), the GRB prompt emission spectra would include a dominant thermal component originating from the fireball photosphere, and a non-thermal component presumably originating from internal shocks whose radii are greater than the photosphere radius. We propose a method to directly dissect the GRB fireball energy budget into three components and measure their values by combining the prompt emission and early afterglow data. The measured parameters include the initial dimensionless specific enthalpy density ($\eta$), bulk Lorentz factors at the photosphere radius (${\Gamma }_{\mathrm{ph}}$) and before fireball deceleration (${\Gamma }_0$), the amount of mass loading ($M$), as well as the GRB radiative efficiency (${\eta }_{\gamma }$). All the parameters can be derived from the data for a GRB with a dominant thermal spectral component, a deceleration bump feature in the early afterglow lightcurve, and a measured redshift. The results only weakly depend on the density $n$ of the interstellar medium when the composition $\mathcal{Y}$ parameter (typically unity) is specified.

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References in corpus (14)

• The Physics of Gamma-Ray Bursts and Relativistic Jets
• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short
• Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
• A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. I. Spectral Components and Their Possible Physical Origins of LAT/GBM GRBs
• REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination
• GRB110721A: An extreme peak energy and signatures of the photosphere
• Quasi-blackbody component and radiative efficiency of the prompt emission of gamma-ray bursts
• A new method of determining the initial size and Lorentz factor of gamma-ray burst fireballs using a thermal emission component
• Bulk Lorentz factors of Gamma-Ray Bursts
• Photosphere emission from a hybrid relativistic outflow with arbitrary dimensionless entropy and magnetization in GRBs
• 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

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