Eight Gamma-Ray Bursts Observed with the Fermi Gamma-ray Burst Monitor: Significant Quasi-Thermal Components and Conditional Jet Constraints
Abstract
The composition of gamma-ray burst (GRB) jets remains uncertain. We analyze eight Fermi Gamma-ray Burst Monitor (GBM) GRBs with reported redshift information, selected from 126 events by prespecified fluence and spectral criteria. After excluding compound-model DIC evaluations classified as unstable by the posterior-stability tests, a stable added-blackbody (BB) comparison gives ΔDIC>10 in 203 of 215 accepted bins (60--100\% per burst); independently, a multicolor-blackbody plus power-law (mBB+PL) decomposition gives FmBB/Ftot>0.5 in 214 of 215 bins. The cutoff-power-law (CPL)--mBB correlations (r=0.83 and 0.78) exceed the Band--mBB correlations (r=0.41 and 0.48), demonstrating model dependence. Time-integrated BB fractions span 0.005--0.311, with six of eight below 0.12. We then apply the non-dissipative photosphere prescriptions of \citet{2013A&A...551A.124H} (H2013) and \citet{2015ApJ...801..103G} (G2015). After excluding boundary or physically inadmissible inversions, the H2013 numbers with εTh>0.5 are 1/2, 1/4, and 2/8 among valid solutions at R0=21, 100, and 1000~km, respectively; the corresponding G2015 numbers with σ0<1 are 0/1, 1/4, and 1/8. The large number of invalid solutions at small R0 (six and seven at 21~km for H2013 and G2015) is itself evidence that those assumed radii are incompatible with the adopted inversion for most events. Among bursts having valid solutions at more than one radius, increasing R0 generally lowers εTh and raises σ0. Thus launch radius, efficiency, and spectral decomposition dominate the conditional jet constraints; no universal jet class or unique non-thermal mechanism is inferred.
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BibTeX
@misc{du2026eight,
title = {{Eight Gamma-Ray Bursts Observed with the Fermi Gamma-ray Burst Monitor: Significant Quasi-Thermal Components and Conditional Jet Constraints}},
author = {Ze-lian Du and Zhao-Yang Peng and Jia-Ming Chen and Yue Yin and Ting Li},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.01061},
eprint = {2610.01061},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.01061},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Eight Gamma-Ray Bursts Observed with the Fermi Gamma-ray Burst Monitor: Significant Quasi-Thermal Components and Conditional Jet Constraints
AU - Ze-lian Du
AU - Zhao-Yang Peng
AU - Jia-Ming Chen
AU - Yue Yin
AU - Ting Li
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.01061
UR - https://arxiv.org/abs/2610.01061
AB - The composition of gamma-ray burst (GRB) jets remains uncertain. We analyze eight Fermi Gamma-ray Burst Monitor (GBM) GRBs with reported redshift information, selected from 126 events by prespecified fluence and spectral criteria. After excluding compound-model DIC evaluations classified as unstable by the posterior-stability tests, a stable added-blackbody (BB) comparison gives ΔDIC>10 in 203 of 215 accepted bins (60--100\% per burst); independently, a multicolor-blackbody plus power-law (mBB+PL) decomposition gives F_mBB/F_tot>0.5 in 214 of 215 bins. The cutoff-power-law (CPL)--mBB correlations (r=0.83 and 0.78) exceed the Band--mBB correlations (r=0.41 and 0.48), demonstrating model dependence. Time-integrated BB fractions span 0.005--0.311, with six of eight below 0.12. We then apply the non-dissipative photosphere prescriptions of \citet{2013A&A...551A.124H} (H2013) and \citet{2015ApJ...801..103G} (G2015). After excluding boundary or physically inadmissible inversions, the H2013 numbers with ε_Th>0.5 are 1/2, 1/4, and 2/8 among valid solutions at R_0=21, 100, and 1000~km, respectively; the corresponding G2015 numbers with σ_0<1 are 0/1, 1/4, and 1/8. The large number of invalid solutions at small R_0 (six and seven at 21~km for H2013 and G2015) is itself evidence that those assumed radii are incompatible with the adopted inversion for most events. Among bursts having valid solutions at more than one radius, increasing R_0 generally lowers ε_Th and raises σ_0. Thus launch radius, efficiency, and spectral decomposition dominate the conditional jet constraints; no universal jet class or unique non-thermal mechanism is inferred.
ER -