Closure relations of Gamma Ray Bursts in high energy emission

Abstract

The synchrotron external shock model predicts the evolution of the spectral ($\beta$) and temporal ($\alpha$) indices during the gamma-ray burst (GRB) afterglow for different environmental density profiles, electron spectral indices, electron cooling regimes, and regions of the spectrum. We study the relationship between $\alpha$ and $\beta$, the so-called "closure relations" with GRBs detected by \textit{Fermi} Large Area Telescope (\textit{Fermi}-LAT) from 2008 August to 2018 August. The spectral and temporal indices for the > 100 MeV emission from the \textit{Fermi}-LAT as determined in the Second Fermi-LAT Gamma-ray Burst Catalog (2FLGC) are used in this work. We select GRBs whose spectral and temporal indices are well constrained (58 long-duration GRBs and 1 short-duration GRBs) and classify each GRB into the best-matched relation. As a result, we found that a number of GRBs require a very small fraction of the total energy density contained in the magnetic field (${\epsilon }_B$ $\lesssim$ 10${}^{-7}$). The estimated mean and standard deviation of electron spectral index $p$ are 2.40 and 0.44, respectively. The GRBs satisfying a closure relation of the slow cooling tend to have a softer $p$ value compared to those of the fast cooling. Moreover, the Kolmogorov--Smirnov test of the two $p$ distributions from the fast and slow coolings rejects a hypothesis that the two distributions are drawn from the single reference distribution with a significance of 3.2 $\sigma$. Lastly, the uniform density medium is preferred over the medium that decreases like the inverse of distance squared for long-duration GRBs.

References in corpus (19)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• The Supernova -- Gamma-Ray Burst Connection
• The Physics of Gamma-Ray Bursts and Relativistic Jets
• Gamma-Ray Bursts: Progress, Problems & Prospects
• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. I. Spectral Components and Their Possible Physical Origins of LAT/GBM GRBs
• A decade of Gamma-Ray Bursts observed by $Fermi$-LAT: The 2${}^{nd}$ GRB catalog
• Klein-Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum
• The redshift and afterglow of the extremely energetic gamma-ray burst GRB 080916C
• Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow
• Time-Resolved Spectroscopy of the 3 Brightest and Hardest Short Gamma-Ray Bursts Observed with the FGST Gamma-Ray Burst Monitor
• Gamma-Ray Burst Afterglows as Probes of Environment and Blastwave Physics II: the Distribution of p and Structure of the Circumburst Medium
• Clustering of LAT light curves: a clue to the origin of high-energy emission in Gamma-Ray Bursts
• Modeling the early afterglow in the short and hard GRB 090510
• Temporal Evolution of the Gamma-ray Burst Afterglow Spectrum for an Observer: GeV--TeV Synchrotron Self-Compton Light Curve
• GRB Observational Properties
• High-Energy Non-Thermal and Thermal Emission from GRB141207A detected by Fermi
• Time evolution of the spectral break in the high-energy extra component of GRB 090926A
• Multiple Components in the Broadband $\gamma$-ray Emission of the Short GRB 160709A

Cited by in corpus (3)

• On the Existence of the Plateau Emission in High-Energy Gamma-Ray Burst LightCurves observed byFermi-LAT
• The closure relations in optical afterglow of Gamma-Ray Bursts
• Closure Relations of Synchrotron Self-Compton in Afterglow stratified medium and Fermi-LAT Detected Gamma-Ray Bursts