Spectral-Lag Relations in GRB Pulses Detected with HETE-2

Using a pulse-fit method, we investigated the spectral lags between the traditional gamma-ray band (50–400 keV) and the X-ray band (6–25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, and GRB 050408), detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We found several relations for individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy, Epeak. The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6–25 keV). Furthermore, we found that the photon energy dependence for the spectral lags can be reconciled with the simple curvature effect model. We discuss the implications of these results from various points of view.