Issue |
A&A
Volume 693, January 2025
|
|
---|---|---|
Article Number | A156 | |
Number of page(s) | 15 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361/202451776 | |
Published online | 14 January 2025 |
Gamma-ray burst spectral-luminosity correlations in the synchrotron scenario
1
Gran Sasso Science Institute (GSSI), Via F. Crispi 7, 67100 L’Aquila, Italy
2
INFN–Laboratori Nazionali del Gran Sasso, I-67100 L’Aquila (AQ), Italy
⋆ Corresponding author; alessio.mei@gssi.it
Received:
2
August
2024
Accepted:
15
November
2024
Context. For over two decades, gamma-ray burst (GRB) prompt emission spectra were modeled with smoothly broken power laws (Band function), and a positive and tight correlation between the spectral rest-frame peak energy, Ep,z, and the total isotropic-equivalent luminosity, Liso, was found, constituting the so-called Yonetoku relation. However, more recent studies show that many prompt emission spectra are well described by the synchrotron radiation model, and hence significantly deviate from the Band function.
Aims. In this work, we test the impact of a more refined spectral model such as an idealized synchrotron spectrum from nonthermal electrons on the Yonetoku relation and its connection with physical parameters.
Methods. We selected GRBs with measured redshift observed by Fermi/GBM together with high-energy observations (> 30 MeV), and performed a spectral analysis, dividing them in two samples: the single-bin sample, using the light curve peak spectrum of each GRB, and the multiple-bin sample, for which we explored the whole duration of 13 bright bursts with time-resolved spectral analysis.
Results. We observed that the Ep,z of synchrotron spectra in a fast-cooling regime (νm/νc ≫ 1) is generally larger than the one provided by the Band function. For this reason, we do not find any Ep,z−Liso correlation in our samples except for the GRBs in an intermediate-cooling regime (1< νm/νc< 3); namely, where peak and break energies are very close. We instead find in both our samples a new tight correlation between the rest-frame cooling frequency, νc, z, and Liso: νc,z ∝ Liso(0.53±0.06).
Conclusions. These results suggest that, assuming that prompt emission spectra are produced by synchrotron radiation, the physical relation is between νc, z and Liso. The fit of the Band function to an intrinsic synchrotron spectrum returns peak energy values of Ep,zBand ∼ νc,z. This may explain why the systematic interpretation of prompt spectra through the Band function returns the Ep, z − Liso relation.
Key words: astroparticle physics / radiation mechanisms: non-thermal / gamma-ray burst: general / gamma rays: general
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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