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Fast-cooling Synchrotron in Decaying Magnetic Fields: Implications for the Gamma-Ray Burst Spectral Distribution
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DOI：10.3847/1538-4357/ae633c.png)
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Abstract
En 中文
The prompt emission spectra of gamma-ray bursts (GRBs) are commonly described by the empirical Band function. The typical low-energy spectral index is similar to-1, which poses a challenge to standard synchrotron radiation models. We systematically investigate a fast-cooling synchrotron model with a decaying magnetic field and test, within an observation-consistent pipeline, whether it reproduces the Band-fit parameter distributions in the Gamma-Ray Burst Monitor (GBM) catalog, in a statistical sense. We solve the electron continuity equation with synchrotron, adiabatic, and synchrotron self-Compton (SSC) cooling to obtain the time-dependent electron distribution and synthetic spectra; we then forward-fold through the GBM response matrices and recover (alpha, beta, Ep) with Band fits. We find that magnetic-field decay can harden the recovered alpha relative to the fast-cooling limit in part of parameter space, but the effect is not robust and is sensitive to the location of Ep within the finite band and to spectral curvature; varying key physical scales reshapes the recovered alpha distribution, indicating that catalog alpha often represents an effective in-band slope rather than the asymptotic index. SSC cooling provides modest additional hardening and, in our setups, does not stabilize alpha near the observed peak. Using Monte Carlo samples designed to mimic the observations, the model yields alpha mostly between -1.5 and -0.8, but remains centered around alpha approximate to -1.5. Overall, while a decaying-field fast-cooling synchrotron can partially alleviate overly soft spectra expected from standard fast-cooling synchrotron emission, it still falls short of reproducing the GBM alpha distribution at the population level, implying that additional physical processes are required.
Keywords:
PROMPT EMISSION
PHOTOSPHERIC EMISSION
LIGHT CURVES
SHOCK MODEL
EVOLUTION
CATALOG
RADIATION
GBM
I.
COMPONENTS
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5.4
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8.3W
Citations:
32.0W
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