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arXiv · 2503.17216

High energy time lags of Gamma Ray Bursts

C. Maraventano·G. Ghirlanda·L. Nava·T. Di Salvo·W. Leone·R. Iaria·L. Burderi·A. Tsvetkova
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Abstract

Positive lags between the arrival time of different photon energies are commonly observed in Gamma-Ray Bursts (GRBs), where soft photons lag behind harder ones. However, some GRBs exhibit the opposite behavior. In particular, Fermi LAT observations have revealed that high-energy photons often have a delayed onset. We explore spectral lags as a tool to identify emission components, analyzing Fermi GBM and LAT Low Energy (LLE) data. Using the Discrete Correlation Function method, we compute spectral lags in four energy bands (10 keV-100 MeV) for 70 GRBs from the LLE Catalog. Lags between 10 keV and 1 MeV are mostly positive (76%), possibly due to a hard-to-soft spectral evolution. However, lags between the LLE band (30-100 MeV) and GBM (10-100 keV) vary: 40% are positive, while 37% are negative. These negative lags suggest the delayed emergence of an additional high-energy component. Spectral analysis of 56 GRBs reveals that negative lags correspond to an LLE spectral index harder than the GBM high-energy power law. LLE spectral lags can thus serve as a diagnostic tool to identify and characterize emission components, emphasizing the importance of combining temporal and spectral analyses to better understand GRB emission mechanisms.

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C. Maraventano, G. Ghirlanda, L. Nava, T. Di Salvo, W. Leone, R. Iaria, L. Burderi, A. Tsvetkova. 2025-03-21. High energy time lags of Gamma Ray Bursts. https://doi.org/10.1051/0004-6361%2F202554053

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