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arXiv 0909.5247astro-ph.HE
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用Swift数据研究长伽马射线暴的起源性质

Towards the Properties of Long Gamma-Ray Burst Progenitors with Swift Data

Xiao-Hong Cui, En-Wei Liang, Hou-Jun Lv, Bin-Bin Zhang, Ren-Xin Xu

摘要:

本文以33个雨燕伽玛暴为例,研究了伽马射线暴的瞬发余辉和X射线余辉的性质。假设正则X射线余辉光变曲线中的陡峭衰减段是由于曲率效应,我们用破幂律拟合光变曲线,导出瞬发最后一个发射历元的零点时间(t1)和浅衰变段的开始和结束时间(t2和t3).我们发现各向同性的峰值γ射线亮度和γ射线能量都与浅衰变相的各向同性X射线能量和t2时的各向同性X射线亮度相关. Kumar等人提出了一个模型,认为瞬发γ射线和X射线余辉都是由于中央黑洞吸积了GRB祖星的不同层物质,我们根据该模型推断了祖星的性质。我们发现,大多数核心层的导出质量为0.1-5太阳质量,半径为10^8-10^10 cm。旋转参数与爆发持续时间相关,与BMSAR模型的预期一致。包层回落物质的半径和质量估计分别为10 ^10 - 10 ^12 cm和10^-3~1太阳质量。在浅衰变阶段的平均吸积率与瞬发γ射线阶段的平均吸积率相关,但它们要低得多。导出的包层半径小于沃尔夫-拉叶星的光球半径。有趣的是,我们样本中爆发的质量密度分布也与25个太阳质量的前超新星恒星的模拟一致。

英文摘要:

We investigate the properties of both the prompt and X-ray afterglows of gamma-ray bursts (GRBs) in the burst frame with a sample of 33 Swift GRBs. Assuming that the steep decay segment in the canonical X-ray afterglow lightcurves is due to the curvature effect, we fit the lightcurves with a broken power-law to derive the zero time of the last emission epoch of the prompt emission (t1) and the beginning as well as the end time of the shallow decay segment (t2 and t3).We show that both the isotropic peak gamma-ray luminosity and gamma-ray energy are correlated with the isotropic X-ray energy of the shallow decay phase and the isotropic X-ray luminosity at t2. We infer the properties of the progenitor stars based on a model proposed by Kumar et al. who suggested that both the prompt gamma-rays and the X-ray afterglows are due to the accretions of different layers of materials of the GRB progenitor star by a central black hole (BH). We find that most of the derived masses of the core layers are 0.1-5 solar mass with a radius of 10^8-10^10 cm. The rotation parameter is correlated with the burst duration, being consistent with the expectation of collapsar models. The estimated radii and the masses of the fall-back materials for the envelope layers are 10^10-10^12 cm and 10^-3~1 solar mass, respectively. The average accretion rates in the shallow decay phase are correlated with those in the prompt gamma-ray phase, but they are much lower. The derived radii of the envelope are smaller than the photospheric radii of Wolf-Rayet (WR) stars. It is interesting that the assembled mass density profile for the bursts in our sample is also well consistent with the simulation for a pre-supernova star with 25 solar mass.

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