Observational characteristics of radiation-mediated shocks in photospheric gamma-ray burst emission

Abstract

Emission from the photosphere in gamma-ray burst (GRB) jets can be substantially affected by subphotospheric energy dissipation, which is typically caused by radiation-mediated shocks (RMSs). We study the observational characteristics of such emission, in particular the spectral signatures. Relevant shock initial conditions are estimated using a simple internal collision framework, which then serve as inputs for an RMS model that generates synthetic photospheric spectra. Within this framework, we find that if the free fireball acceleration starts at $r_0\sim 10^{10}$cm, in agreement with hydrodynamical simulations, then the typical spectrum consists of a broad, soft power-law segment with a cutoff at high energies and a hardening in X-rays. The synthetic spectra are generally well fitted with a standard cutoff power-law (CPL) function, as the hardening in X-rays is commonly outside the observable energy range of current detectors. The CPL-fits yield values for the low-energy index, $\alpha$, and the peak energy, $E_{\mathrm{peak}}$, that are centered around $\sim -0.8$ and $\sim 220$keV, respectively, similar to typical observed values. We also identify a non-negligible parameter region for what we call ``optically shallow shocks'': shocks that do not accumulate enough scatterings to reach a steady-state spectrum before decoupling and thereby produce more complex spectra. These occur for optical depths $\tau \lesssim 55u_u^{-2}$, where $u_u={\gamma }_u{\beta }_u$ is the dimensionless specific momentum of the upstream as measured in the shock rest frame.

Manuscript accepted by ApJ. Updated to match accepted version

References in corpus (22)

• Temporal Evolution Of Thermal Emission From Relativistically Expanding Plasma
• Very high efficiency photospheric emission in long duration gamma-ray bursts
• The Fermi GBM Gamma-Ray Burst Spectral Catalog: 10 Years of Data
• The structure of hydrodynamic $\gamma$-ray burst jets
• The case for a minute-long merger-driven gamma-ray burst from fast-cooling synchrotron emission
• Relativistic Radiation Mediated Shocks
• Evidence of two spectral breaks in the prompt emission of gamma ray bursts
• Uncovering the Intrinsic Variability of Gamma-ray Bursts
• Relativistic Photon Mediated Shocks
• High efficiency photospheric emission entailed by formation of a collimation shock in gamma-ray bursts
• Evidence for jet launching close to the black hole in GRB 101219B - a Fermi GRB dominated by thermal emission
• Monte-Carlo simulations of relativistic radiation mediated shocks: I. photon rich regime
• Bayesian Time-Resolved Spectroscopy of Multi-Pulsed GRBs: Variations of Emission Properties amongst Pulses
• Monte Carlo simulations of the photospheric emission in GRBs
• Non-dissipative photospheres in GRBs: Spectral appearance in the Fermi/GBM catalogue
• Emission from accelerating jets in gamma-ray bursts: Radiation dominated flows with increasing mass outflow rates
• Sub-photospheric, radiation mediated shocks in GRBs: Multiple shock emission and the Band spectrum
• Plasma kinetic effects in relativistic radiation mediated shocks
• A first-principle simulation of blast wave emergence at the photosphere of a neutron star merger
• An efficient method for fitting radiation-mediated shocks to gamma-ray burst data: The Kompaneets RMS approximation
• Onset of particle acceleration during the prompt phase in gamma-ray bursts as revealed by synchrotron emission in GRB160821A
• Photons' scattering in a relativistic plasma with velocity shear: generation of high energy power-law spectra

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• Radiation-mediated shocks in gamma-ray bursts: spectral evolution
• EP241113a: dissipative photospheric emission from a dirty fireball
• Magnetized Shocks Mediated by Radiation from Leptonic and Hadronic Processes