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arXiv 0806.1278astro-ph
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伽玛暴980425和060218的宽带光变曲线特征及其与长滞后宽脉冲伽玛暴的比较

Broadband lightcurve characteristics of GRBs 980425 and 060218 and comparison with long-lag, wide-pulse GRBs

Fu-Wen Zhang

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26 pages, 10 figures, 3 tables, accepted for publication in ApJ
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摘要：

近年来，低光度伽马射线暴（LL-GRB）可能是一种独特的GRB群。在这里，我们提出了系统的分析的光变曲线的特点，从X射线到伽马射线的能量带的两个原型LL-GRB 980425和060218。结果表明，这两个脉冲的脉冲宽度（$w$）和上升宽度与衰减宽度之比（$r/d$）在较宽的能量带内都是能量相关的。对于这两个事件，存在一个明显的趋势，即脉冲倾向于更窄并且相对于更高的能带更对称。X射线和γ射线都遵循相同的$w - E$和$r/d - E$关系。这些事实可能表明，X射线发射跟踪伽马射线发射，两者可能源于相同的物理机制。它们的光变曲线显示出明显的光谱滞后。我们用脉冲峰值时间（$t_{peak}$）、脉冲中心时间（$t_{cen}$）和交叉关联函数（CCF）计算了三种类型的滞后。导出的$t_{peak}$和$t_{cen}$是能量的幂律函数。由CCF计算的滞后与从$t_{peak}$导出的滞后密切相关。但由$t_{cen}$导出的滞后与由$t_{peak}$和CCF导出的滞后的相关性较小。在较高的能带处，滞后的能量依赖性较浅。这些特征与典型的长滞后、宽脉冲伽玛暴的观测结果一致，表明980425和060218伽玛暴可能具有与它们相似的辐射物理性质。

英文摘要：

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 lightcurve 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 symmetry with respect to the 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 be originated 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 a power-law function of energy. The lag calculated by CCF is strongly correlated with that derived from $t_{peak}$. But the lag derived from $t_{cen}$ is less correlated with that derived from $t_{peak}$ and CCF. The energy dependence of the lags is shallower at higher energy bands. These characteristics are well consistent with that observed in typical long-lag, wide-pulse GRBs, suggesting that GRBs 980425 and 060218 may share the similar radiation physics with them.

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