Towards an understanding of GRB prompt emission mechanism: I. The origin of spectral lags

Abstract

Despite decades of investigations, the physical mechanism that powers the bright prompt $\gamma$-ray emission from gamma-ray bursts (GRBs) is still not identified. One important observational clue that remains not properly interpreted so far is the existence of time lags of broad light curve pulses in different energy bands, named "spectral lags". Here we show that the traditional view invoking the high-latitude emission "curvature effect" of a relativistic jet cannot account for spectral lags. Rather, the observed spectral lags demand the sweep of a spectral peak across the observing energy band in a specific manner. The duration of the broad pulses and inferred typical Lorentz factor of GRBs require that the emission region is in an optically thin emission region far from the GRB central engine. We construct a simple physical model invoking synchrotron radiation from a rapidly expanding outflow. We show that the observed spectral lags appear naturally in our model light-curves given that (1) the gamma-ray photon spectrum is curved (as observed), (2) the magnetic field strength in the emitting region decreases with radius as the region expands in space, and (3) the emission region itself undergoes rapid bulk acceleration as the prompt $\gamma$-rays are produced. These requirements are consistent with a Poynting-flux-dominated jet abruptly dissipating magnetic energy at a large distance from the engine.

10 pages, 4 figures, accepted for publication in ApJ

References in corpus (12)

• The Physics of Gamma-Ray Bursts and Relativistic Jets
• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs
• Prompt GRB emission from gradual energy dissipation
• A Comprehensive Analysis of Fermi Gamma-ray Burst Data: II. $E_{\mathrm{p}}$-Evolution Patterns and Implications for the Observed Spectrum-Luminosity Relations
• Physics of Gamma-Ray Bursts Prompt Emission
• Photosphere emission from a hybrid relativistic outflow with arbitrary dimensionless entropy and magnetization in GRBs
• Synchrotron Origin of the Typical GRB Band Function - A Case Study of GRB 130606B
• Relativistic MHD simulations of collision-induced magnetic dissipation in Poynting-flux-dominated jets/outflows
• Confronting GRB prompt emission with a model for subphotospheric dissipation
• An Observed Correlation Between Thermal and Non-Thermal Emission in Gamma-Ray Bursts
• Accounting for the XRT early steep decay in models of the prompt GRB emission

Cited by in corpus (40)

• Neutrino-dominated accretion flows as the central engine of gamma-ray bursts
• Low-energy Spectra of Gamma-ray Bursts from Cooling Electrons
• A New Test of Lorentz Invariance Violation: the Spectral Lag Transition of GRB 160625B
• Gamma Ray Burst Prompt correlations
• GRB 200415A: A Short Gamma-Ray Burst from a Magnetar Giant Flare?
• The Delay Time of Gravitational Wave -- Gamma-Ray Burst Associations
• Toward an understanding of GRB prompt emission mechanism: II. Patterns of peak energy evolution and their connection to spectral lags
• "Double-tracking" Characteristic of the Spectral Evolution of GRB 131231A: Synchrotron Origin?
• A New Measurement of the Spectral Lag of Gamma-Ray Bursts and its Implications for Spectral Evolution Behaviors
• Gamma-ray Bursts Induced by Turbulent Reconnection
• GRB 210121A: A Typical Fireball Burst Detected by Two Small Missions
• Lorentz Invariance Violation Limits from the Spectral Lag Transition of GRB~190114C
• Time-Resolved and Energy-Resolved Polarizations of GRB Prompt Emission
• Synchrotron radiation in $\gamma$-ray burst prompt emission
• A comprehensive analysis of Fermi Gamma-Ray Burst Data: IV. Spectral lag and Its Relation to Ep Evolution
• Temporal Evolution of Prompt GRB Polarization
• Testing High-latitude Curvature Effect of Gamma-Ray Bursts with {\it Fermi} Data: Evidence of Bulk Acceleration in Prompt Emission
• GRB Observational Properties
• Steep Decay of GRB X-ray Flares: the Result of Anisotropic Synchrotron Radiation
• Constraints on quantum gravity and the photon mass from gamma ray bursts
• The Synchrotron Polarization in Decaying Magnetic Field in Gamma-Ray Bursts
• Synchrotron radiation from electrons with a pitch-angle distribution
• Spectral Lag Transition of 32 Fermi Gamma-ray Bursts and their Application on Constraining Lorentz Invariance Violation
• Gamma-ray Burst Prompt Emission Spectrum and $E_p$ Evolution Patterns in the ICMART Model
• Revisiting Tests of Lorentz Invariance with Gamma-ray Bursts: Effects of Intrinsic Lags
• Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM
• Rotation of polarization angle in gamma-ray burst prompt phase
• Modelling the prompt optical emission of GRB 180325A: the evolution of a spike from the optical to gamma-rays
• One Fits All: A Unified Synchrotron Model Explains GRBs with FRED-Shaped Pulses
• Constraints on Equivalence Principle Violation from Gamma Ray Bursts
• Spectral Lag for a Radiating Jet Shell with a High Energy Cut-off Radiation Spectrum
• Temporal and Spectral Evolution of Gamma-ray Burst Broad Pulses: Identification of High Latitude Emission in the Prompt Emission
• LOFAR detectability of prompt low-frequency radio emission during gamma-ray burst X-ray flares
• Spectral evolution responsible for the transition from positive lags to negative lags in Gamma-ray Bursts
• A Spectral Analysis of Fermi-LLE GRBs
• Probing the progenitor of high-$z$ short-duration GRB 201221D and its possible bulk acceleration in prompt emission
• A Concept of Assessment of LIV Tests with THESEUS Using the Gamma-Ray Bursts Detected by Fermi/GBM
• High energy time lags of Gamma Ray Bursts
• Jet-Structure Imprint on the Curvature Tail of Gamma-Ray Burst Prompt Emission
• Outliers in spectral time lag selected gamma-ray bursts