2019ApJ...882..115D

Recent research shows that the spectral lag is closely related to the spectral evolution in gamma-ray bursts (GRBs). In this paper, we study the spectral lag for a radiating jet shell with a high-energy cutoff radiation spectrum. For the jet shell with a cutoff power-law spectrum, the spectral lag monotonically increases with the photon energy and levels off at a certain photon energy. It is the same for the jet shell with a Band cutoff spectrum (Bandcut). However, a turnover from the positive lags to negative lags appears in the high-energy range for the jet shell with a Bandcut, which is very similar to that observed in GRB 160625B. The dependence of the spectral lags on the spectral shape/evolution is studied in detail. In addition, the spectral lag behavior observed in GRB 160625B is naturally reproduced based on our theoretical outcome.