Spectral lags caused by the curvature effect of fireballs
Spectral lags caused by the curvature effect of fireballs
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DOI：
10.1111/j.1365-2966.2005.09951.x
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发表时间：
2005-09
影响因子：
4.8
通讯作者：
R. Lu;Y.-P. Qin;Z.-B. Zhang;T. Yi
中科院分区：
文献类型：
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作者：
R. Lu;Y.-P. Qin;Z.-B. Zhang;T. Yi
最近，Shen等人研究了火球曲率效应对光谱滞后的贡献，并表明观测到的滞后可以用该效应来解释。在这里，我们通过对Shen等人和Qin等人提出的公式进行更精确的计算来验证他们的结果。本文还研究了Shen等人未考虑的其他几个方面。我们发现，在超相对论性运动的情况下，只要考虑整个火球表面，两个公式是相同的。在我们的分析中，证实了之前的结论，即探测到的光谱滞后可以用曲率效应来解释，而滞后与火球半径无关的结论是不成立的。我们发现引入极端物理参数并不是解释这些观测到的大滞后的唯一出路。即使对于较大的滞后（类似于5秒），更宽的局部脉冲(δ t（θ，FWHM)= 10(7)秒）也可以解释它。下面列出了Shen等人没有提出的一些结论或我们在分析中修改的一些结论：(i)与Gamma（-epsilon）成正比的滞后与epsilon bbb2；（ii）滞后与局部脉冲宽度和观测到的光曲线的半最大值处的全宽度成正比；（iii）大滞后需要大的α(0)和小的β(0)以及大的E-0，E-p；（iv）当静帧频谱随时间变化时，滞后性会变大；(v)滞后随R-c的增大而减小；（vi）给定洛伦兹因子在一定能量范围内与E成正比的滞后；（vii）当theta(j) < 0.6 Gamma（-1）时，滞后与均匀射流的开口角成正比。
Recently, Shen et al. have studied the contributions of the curvature effect of fireballs to the spectral lag and have shown that the observed lags can be accounted for by the effect. Here, we check their results by performing a more precise calculation with both formulae presented by Shen et al. and Qin et al. Several other aspects which were not considered by Shen et al. are investigated. We find that in the case of ultrarelativistic motions, both formulae are identical as long as the whole fireball surface is concerned. In our analysis, the previous conclusion that the detected spectral lags can be accounted for by the curvature effect is confirmed, while the conclusion that the lag has no dependence on the radius of fireballs is not true. We find that introducing extreme physical parameters is not the only outlet to explain these observed large lags. Even for the larger lags (similar to 5 s), a wider local pulse (Delta t(theta,FWHM)= 10(7) s) can account for it. Some conclusions not presented in Shen et al. or those modified in our analysis are listed below: (i) lag proportional to Gamma(-epsilon) with epsilon > 2; (ii) lag is proportional to the local pulse width and the full width at half-maximum of the observed light curves; (iii) a large lag requires a large alpha(0) and a small beta(0) as well as a large E-0,E-p; (iv) when the rest-frame spectrum varies with time, the lag would become larger; (v) lag decreases with the increase of R-c; (vi) lag proportional to E within the certain energy range for a given Lorentz factor; (vii) lag is proportional to the opening angle of uniform jets when theta(j) < 0.6 Gamma(-1).