High energy time lags of Gamma Ray Bursts

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.

18 pages, 11 figures, Submitted to Astronomy & Astrophysics (A&A)

References in corpus (17)

• 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
• Short versus Long Gamma-Ray Bursts: spectra, energetics, and luminosities
• The Konus-Wind catalog of gamma-ray bursts with known redshifts. I. Bursts detected in the triggered mode
• Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow
• Comparing the spectral lag of short and long gamma-ray bursts and its relation with the luminosity
• Correlations Between Lag, Luminosity, and Duration in Gamma-ray Burst Pulses
• Time-Resolved Spectroscopy of the 3 Brightest and Hardest Short Gamma-Ray Bursts Observed with the FGST Gamma-Ray Burst Monitor
• On the Spectral Lags of the Short Gamma-Ray Bursts
• A New Test of Lorentz Invariance Violation: the Spectral Lag Transition of GRB 160625B
• Spectral evolution in gamma-ray bursts: predictions of the internal shock model and comparison to observations
• GRB 190114C: from prompt to afterglow?
• GRB 211211A: a Neutron Star$-$White Dwarf Merger?
• High-Energy Non-Thermal and Thermal Emission from GRB141207A detected by Fermi
• Time delays between Fermi LAT and GBM light curves of GRBs
• A backscattering dominated prompt emission model for the prompt phase of Gamma ray bursts
• The Origin of the Photospheric Emission of GRB 220426A