Origin for the Prompt Spectral Evolution Characteristics and High Energy Emission during the X-Ray Flare in GRB 180720B

Abstract

The gamma-ray burst GRB 180720B is very peculiar. On one hand, some interesting features have been found by performing the detailed time-resolved spectral analysis in the prompt phase. First, the `flux-tracking' pattern is exhibited both for the low energy spectral index $\alpha$ and the peak energy $E_p$ in the Band function. Second, some parameter relations show strong monotonous positive correlations, include $E_p-F$, $\alpha -F$, $E_p-\alpha$, and $E_p-L_{\gamma ,iso}$ for all time-resolved spectra. Lastly, it should be noted that the values of $\alpha$ do not exceed the synchrotron limits (from $-\frac{3}{2}$ to $-\frac{2}{3}$). On the other hand, the photons with the energy of $\gtrsim$ 100 MeV were detected by LAT both in the prompt phase and afterglow. Notably, the 5 GeV photon was observed at 142 s after the GBM trigger. The spectrum of this burst in the LAT range can be described as $F_{\nu }\propto {\nu }^{-1.3}{t}^{-1.54\pm 0.02}$ in the afterglow phase. And there are six GeV photons during the X-ray flare when the lower energy emission is fading to a weaker level. We try to give reasonable interpretations of the mechanism for prompt emission and the high energy emission (100 MeV to GeV) in the afterglow. The interpretations suggesting that synchrotron origin can account for the prompt emission and synchrotron self-Compton radiation can account for both the spectrum and temporal behavior of the 100 MeV to GeV afterglow emission that have been accepted by us.

arXiv commentpublished by ApJ

References in corpus (50)

• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• Collapsars - Gamma-Ray Bursts and Explosions in "Failed Supernovae"
• Spectra and Light Curves of Gamma-Ray Burst Afterglows
• The Supernova -- Gamma-Ray Burst Connection
• Gamma-Ray Bursts as the Death Throes of Massive Binary Stars
• Physical processes shaping GRB X-ray afterglow lightcurves: theoretical implications from the Swift XRT observations
• The Physics of Gamma-Ray Bursts and Relativistic Jets
• Gamma-Ray Bursts: Progress, Problems & Prospects
• The Shape of Spectral Breaks in GRB Afterglows
• Lower Limits on Lorentz Factors in Gamma Ray Bursts
• The Complete Spectral Catalog of Bright BATSE Gamma-Ray Bursts
• The Synchrotron Shock Model Confronts a `Line of Death' in the BATSE Gamma-Ray Burst Data
• The prompt energy release of gamma-ray bursts using a cosmological k-correction
• Gamma-ray burst early optical afterglows: implications for the initial Lorentz factor and the central engine
• The First Fermi LAT Gamma-Ray Burst Catalog
• Fermi-LAT Observations of the Gamma-ray Burst GRB 130427A
• An analysis of gamma-ray burst spectral break models
• A decade of Gamma-Ray Bursts observed by $Fermi$-LAT: The 2${}^{nd}$ GRB catalog
• On the generation of high energy photons detected by the Fermi Satellite from gamma-ray bursts
• BATSE Observations of Gamma-Ray Burst Spectra. II. Peak Energy Evolution in Bright, Long Bursts -
• GeV emission from Gamma Ray Bursts: a radiative fireball?
• Delayed Gev Emission from Cosmological Gamma-Ray Bursts : Impact of a Relativistic Wind on External Matter
• Evolution of the Low-Energy Photon Spectra in Gamma-Ray Bursts
• A Comprehensive Analysis of Fermi Gamma-ray Burst Data: II. $E_{\mathrm{p}}$-Evolution Patterns and Implications for the Observed Spectrum-Luminosity Relations
• Gamma-Ray Burst Spectral Evolution Through Crosscorrelations of Discriminator Light Curves
• High Energy Afterglow from Gamma-ray Bursts
• The Fermi GBM gamma-ray burst time-resolved spectral catalog: brightest bursts in the first four years
• Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow
• Low Energy Spectral Index and $E_p$ evolution of Quasi-thermal Photosphere Emission of Gamma-Ray Bursts
• GeV-TeV and X-ray flares from gamma-ray bursts
• Possible Origins of Dispersion of the Peak Energy--Brightness Correlations of Gamma-Ray Bursts
• High energy gamma-ray emission from Gamma-Ray Bursts -- before GLAST
• Expected high energy emission from GRB 080319B and origins of the GeV emission of GRBs 080514B, 080916C and 081024B
• On the High Energy Emission of the Short GRB 090510
• Low-energy Spectra of Gamma-ray Bursts from Cooling Electrons
• GRB 080916C and GRB 090510: the high energy emission and the afterglow
• MultiPulse {\it Fermi} Gamma-Ray Bursts. I. Evidence of the Transition from Fireball to Poynting-flux-dominated Outflow
• Toward an understanding of GRB prompt emission mechanism: II. Patterns of peak energy evolution and their connection to spectral lags
• The time-resolved spectra of photospheric emission from a structured jet for gamma-ray bursts
• Detection of High-Energy Gamma-Ray Emission during the X-ray flaring activity in GRB100728A
• Sub-GeV flashes in $\gamma -$ray burst afterglows as probes of underlying bright UV flares
• Clustering of gamma-ray burst types in the Fermi-GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phase
• On the Shape of Pulse Spectra in Gamma-Ray Bursts
• The $E_p$ Evolutionary Slope within the Decay Phase of "FRED" Gamma-ray Burst Pulses
• Origin of the GeV Emission During the X-ray Flaring Activity in GRB 100728A
• The synchrotron-self-Compton radiation accompanying shallow decaying X-ray afterglow: the case of GRB 940217
• GRB 131231A: Implications of the GeV emission
• Bulk Compton Emission in the GRB Internal Shock Model
• GeV Emission during X-Ray Flares from Late Internal Shocks: Application to GRB 100728A
• 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

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• Nearby SN-Associated GRB~190829A: Environment, Jet Structure, and VHE Gamma-Ray Afterglows
• Synchrotron Self-Compton Emission in the Two-Component Jet Model for Gamma-Ray Bursts
• The Photosphere Emission Spectrum of Hybrid Relativistic Outflow for Gamma-ray Bursts
• Fires in the deep: The luminosity distribution of early-time gamma-ray-burst afterglows in light of the Gamow Explorer sensitivity requirements
• Afterglow Synchrotron Radiations follow the $L_{\mathrm{p},\mathrm{iso}}-E_{\mathrm{p},\mathrm{z}}-{\Gamma }_0$ relation of Gamma-Ray Bursts? Cases of GRBs 190114C, 130427A, and 180720B
• Hard TeV Gamma-Ray Afterglows of Nearby GRB 190829A as a Tentative Signature of Ultra-High-Energy Cosmic Rays Accelerated in Gamma-Ray Burst Jets
• A Spectral Analysis of Fermi-LLE GRBs