Broadband Light Curve Characteristics of GRBs 980425 and 060218 and Comparison with Long‐Lag, Wide‐Pulse GRBs

Abstract

It has been recently argued that low-luminosity gamma-ray bursts (LL-GRBs) are likely a unique GRB population. Here, we present systematic analysis of the light-curve characteristics from X-ray to gamma-ray energy bands for the two prototypical LL-GRBs, 980425 and 060218. It is found that both the pulse width (w) and the ratio of the rising width to the decaying width (r/d) of theses two bursts are energy-dependent over a broad energy band. There exists a significant trend that the pulses tend to be narrower and more symmetrical at higher energy bands for the two events. Both the X-rays and the gamma-rays follow the same w-E and r/d-E relations. These facts may indicate that the X-ray emission tracks the gamma-ray emission, and both are likely to originate from the same physical mechanism. Their light curves show significant spectral lags. We calculate the three types of lags with the pulse peaking time (t(peak)), the pulse centroid time (t(cen)), and the cross-correlation function (CCF). The derived t(peak) and t(cen) are power-law functions of energy. The lag calculated by CCF is strongly correlated with that derived from tpeak. However, the lag derived from tcen correlates less with that derived from tpeak and CCF. The energy dependence of the lags is shallower at higher energy bands. These characteristics are consistent with that observed in typical long-lag, wide-pulse GRBs, suggesting that GRBs 980425 and 060218 may share a similar radiation physics with them.