GRB120729A: external shock origin for both the prompt gamma-ray emission and afterglow

Abstract

Gamma-ray burst (GRB) 120729A was detected by Swift/BAT and Fermi/GBM, and then rapidly observed by Swift/XRT, Swift/UVOT, and ground-based telescopes. It had a single long and smooth γ-ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II), shallow decay (Phase III), and post-jet break (Phase IV). The spectral energy distribution (SED) evolves from prompt γ-ray emission to the afterglow with photon index from ${\Gamma }_{\gamma }=1.36$ to $\Gamma \approx 1.75$. There is no obvious evolution of the SED during the afterglow. The multiwavelength light curves from γ-ray to optical can be well modeled with an external shock by considering energy injection, and a time-dependent microphysics model with ${\epsilon }_B\propto t^{{\alpha }_B}$ for the emission at early times, $T<T_0+157$~s. Therefore, we conclude that both the prompt γ-ray emission and afterglow of GRB 120729A have the same external shock physical origin. Our model indicates that the ${\epsilon }_B$ evolution can be described as a broken power-law function with ${\alpha }_{\mathrm{B},1}=0.18\pm 0.04$ and ${\alpha }_{\mathrm{B},2}=0.84\pm 0.04$. We also systematically investigate single-pulse GRBs in the Swift era, finding that only a small fraction of GRBs (GRBs 120729A, 051111, and 070318) are likely to originate from an external shock for both the prompt γ-ray emission and afterglow.

arXiv comment23 pages, 9 figures,Accepted for publication in ApJ

References in corpus (53)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Spectra and Light Curves of Gamma-Ray Burst Afterglows
• Optical and Long Wavelength Afterglow from Gamma-Ray Bursts
• Physical processes shaping GRB X-ray afterglow lightcurves: theoretical implications from the Swift XRT observations
• The Physics of Gamma-Ray Bursts and Relativistic Jets
• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• Calibration of X-ray absorption in our Galaxy
• Gamma-ray Burst Afterglow with Continuous Energy Injection: Signature of a Highly-Magnetized Millisecond Pulsar
• Theories of Gamma-Ray Bursts
• Can internal shocks produce the variability in GRBs?
• Steep Slopes and Preferred Breaks in GRB Spectra: the Role of Photospheres and Comptonization
• Gamma-ray bursts from internal shocks in a relativistic wind: temporal and spectral properties
• Refreshed Shocks and Afterglow Longevity in GRB
• A Comprehensive Analysis of the Swift/XRT Data: II. Diverse Physical Origins of the Shallow Decay Segment
• Impulsive and Varying Injection in GRB Afterglows
• Multi-Wavelength Afterglows in Gamma-Ray Bursts: Refreshed Shock and Jet Effects
• A Complete Reference of the Analytical Synchrotron External Shock Models of Gamma-Ray Bursts
• Gamma-ray burst early afterglows: reverse shock emission from an arbitrarily magnetized ejecta
• Constraining GRB Initial Lorentz Factor with the Afterglow Onset Feature and Discovery of a Tight Gamma_0-E_iso Correlation
• On the generation of high energy photons detected by the Fermi Satellite from gamma-ray bursts
• A Generic Dynamical Model of Gamma-ray Burst Remnants
• A Study of the Afterglows of Four GRBs: Constraining the Explosion and Fireball Model
• External forward shock origin of high energy emission for three GRBs detected by Fermi
• Temporal Evolution Of Thermal Emission From Relativistically Expanding Plasma
• Evidence of an initially magnetically dominated outflow in GRB 080916C
• Magnetic Fields In Relativistic Collisionless Shocks
• The Swift Burst Analyser I: BAT and XRT spectral and flux evolution of Gamma Ray Bursts
• A Comprehensive Study of Gamma-Ray Burst Optical Emission: I. Flares and Early Shallow Decay Component
• Open Questions in GRB Physics
• Analysis of the X-ray Emission of Nine Swift Afterglows
• Efficiency Crisis of Swift Gamma-Ray Bursts with Shallow X-ray Afterglows: Prior Activity or Time-Dependent Microphysics?
• A Comprehensive Analysis of Fermi Gamma-ray Burst Data: III. Energy-Dependent T90 Distributions of GBM GRBs and Instrumental Selection Effect on Duration Classification
• A Comprehensive Study of Gamma-Ray Burst Optical Emission: II. Afterglow Onset and Late Re-Brightening Components
• The Early Light Curve of the Optical Afterglow of GRB 021211
• Photosphere emission from a hybrid relativistic outflow with arbitrary dimensionless entropy and magnetization in GRBs
• Short Timescale Variability in the External Shock Model of Gamma Ray Bursts
• The Energy-Dependence of GRB Minimum Variability Timescales
• Uncovering the Intrinsic Variability of Gamma-ray Bursts
• A Comprehensive Radio View of the Extremely Bright Gamma-Ray Burst 130427A
• Early Afterglows of Gamma-Ray Bursts in a Stratified Medium with a Power-Law Density Distribution
• Modeling Gamma-Ray Burst X-Ray Flares within the Internal Shock Model
• GRB 030226 in a Density-Jump Medium
• Dynamics and Afterglow Light Curves of GRB Blast Waves with a Long-lived Reverse Shock
• A morphological analysis of gamma-ray burst early optical afterglows
• Constraining the magnetic field in GRB relativistic collisionless shocks using radio data
• Variation of microphysics in wind bubbles: an alternative mechanism for explaining the rebrightenings in GRB afterglows
• Spectral and temporal analysis of the joint Swift/BAT-Fermi/GBM GRB sample
• GRB 070311: a direct link between the prompt emission and the afterglow
• A test of the power law relationship between gamma-ray burst pulse width ratio and energy expected in fireballs or uniform jets
• An External Shock Origin of GRB $\text{141028A}$
• Prompt Gamma-ray and Early Afterglow Emission in the External Shock Model
• GRB 110530A: Peculiar Broad Bump and Delayed Plateau in Early Optical Afterglows
• A Simple Test of the External Shock Model for the Prompt Emission in Gamma-Ray Bursts

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• GRB 200829A: External Shock Origin of the Very Early Prompt Emission?
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