Jets in a Gamma-Ray Burst During its Prompt Emission: Evolution of Lorentz Factor

Abstract

Knowledge about the Lorentz factor and its evolution of relativistic jets in gamma-ray bursts (GRBs) is crucial to understand their physics. An exact value of bulk Lorentz factor can be estimated based on a high-energy spectral cutoff, which may appear in GRBs' prompt emission owing to the absorption of photon-photon pair production. In this work, we focus on the investigation of the bulk Lorentz factor evolution of jets in an individual burst. Based on \textsl{Fermi} observations, we search for the bursts with multiple $\gamma$-ray pulses characterized by a high-energy spectral cutoff, and nine GRBs are obtained. Together with the estimation of the pulse duration and radiation spectrum, the Lorentz factor of jets corresponding to different pulses in an individual GRB are estimated. It is shown that the Lorentz factor of jets in an individual GRB fluctuates within a certain range and without a general trend in these nine GRBs. In addition, the Lorentz factors of the jets in GRBs~130821A, 160509A and 160625B seem to increase with time. We also study the relations among $L_{\mathrm{iso}}$, $E_{\mathrm{p},\mathrm{z}}$, and $\Gamma$ for the pulses in our sample, which is found to be consistent with that found in previous works.

arXiv commentAccepted for publication in ApJ

References in corpus (62)

• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• The Physics of Gamma-Ray Bursts
• The Fermi Gamma-Ray Burst Monitor
• Unsteady Outflow Models for Cosmological Gamma-Ray Bursts
• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• Predictions for The Very Early Afterglow and The Optical Flash
• Lower Limits on Lorentz Factors in Gamma Ray Bursts
• Efficient acceleration and radiation in Poynting flux powered GRB outflows
• Gamma-Ray Bursts in the Swift Era
• Large scale magnetic fields and their dissipation in GRB fireballs
• Gamma-ray burst early optical afterglows: implications for the initial Lorentz factor and the central engine
• The observable effects of a photospheric component on GRB's and XRF's prompt emission spectrum
• The First Fermi LAT Gamma-Ray Burst Catalog
• Fermi-LAT Observations of the Gamma-ray Burst GRB 130427A
• Teraelectronvolt emission from the $\gamma$-ray burst GRB 190114C
• REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination
• Constraining GRB Initial Lorentz Factor with the Afterglow Onset Feature and Discovery of a Tight Gamma_0-E_iso Correlation
• A Reconnection Switch to Trigger Gamma-Ray Burst Jet Dissipation
• Detection of a spectral break in the extra hard component of GRB 090926A
• Prompt GRB emission from gradual energy dissipation
• Plasmoids in relativistic reconnection, from birth to adulthood: first they grow, then they go
• A new method of determining the initial size and Lorentz factor of gamma-ray burst fireballs using a thermal emission component
• Thermalization in Relativistic Outflows and the Correlation between Spectral Hardness and Apparent Luminosity in Gamma-ray Bursts
• Search for Relativistic Curvature Effects in Gamma-Ray Burst Pulses
• The Escape of High-Energy Photons from Gamma-Ray Bursts
• Photospheric emission as the dominant radiation mechanism in long-duration gamma-ray bursts
• Lorentz Factor-Isotropic Luminosity/Energy Correlations of GRBS and Their Interpretation
• Non-Thermal emission from the photospheres of Gamma-Ray Burst outflows. I: High frequency tails
• Quasi-thermal Comptonization and gamma-ray bursts
• Empirical Constraints on Source Properties and Host Galaxies of Cosmological Gamma-Ray Bursts
• Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts
• A Reverse Shock in GRB 160509A
• Thermal Radiation from GRB Jets
• Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-Energy Emission from Prompt to Afterglow
• Properties of GRB Lightcurves from Magnetic Reconnection
• Theoretical Description Of GRB 160625B with Wind-to-ISM Transition and Implications for a Magnetized Outflow
• Lorentz Factor Constraint from the very early external shock of the gamma-ray burst ejecta
• A Reverse Shock and Unusual Radio Properties in GRB 160625B
• A Tight $L_{\mathrm{p},\mathrm{iso}}-E_{\mathrm{p}}^{\prime }-{\Gamma }_0$ Correlation of Gamma-Ray Bursts
• Temporal Evolution of Pair Attenuation Signatures in Gamma-Ray Burst Spectra
• Theory of photospheric emission from relativistic outflows
• Modeling the observations of GRB 180720B: From radio to sub-TeV gamma-rays
• Prompt GeV Emission from Residual Collisions in GRB Outflows: Evidence from Fermi Observations of GRB 080916c
• Proton-synchrotron as the radiation mechanism of the prompt emission of GRBs?
• GRB Fermi-LAT afterglows: explaining flares, breaks, and energetic photons
• GRB 110731A: Early afterglow in stellar wind powered by a magnetized outflow
• The rise and fall of the high-energy afterglow emission of GRB 180720B
• A comprehensive analysis of Fermi Gamma-Ray Burst Data: IV. Spectral lag and Its Relation to Ep Evolution
• An External Shock Origin of GRB $\text{141028A}$
• GRBs from Magnetic Reconnection: Variability and Robustness of Lightcurves
• The History of GRB Outflows: Ejection Lorentz Factor and Radiation Location of X-Ray Flares
• Radiation from a Relativistic Poynting Jet: some general considerations
• Synchrotron Self-Compton Emission in the Two-Component Jet Model for Gamma-Ray Bursts
• The AGILE observations of the hard and bright GRB 100724B
• A marginally fast-cooling proton-synchrotron model for prompt GRBs
• GRB120729A: external shock origin for both the prompt gamma-ray emission and afterglow
• GRB 220426A: A Thermal Radiation-Dominated Gamma-Ray Burst
• Pair Production Absorption Troughs in Gamma-Ray Burst Spectra: A Potential Distance Discriminator
• Constraining the bulk Lorentz factor from the photosphere emission
• Physical origin of GeV emission in the early phase of GRB 170405A: Clues from emission onsets with multi-wavelength observations
• Lorentz Factor Evolution of an Expanding Jet Shell Observed in Gamma-ray Burst: Case study of GRB 160625B
• High energy emission of GRB 130821A: constraining the density profile of the circum-burst medium as well as the initial Lorentz factor of the outflow