Close binary progenitors of gamma-ray bursts
Close binary progenitors of gamma-ray bursts
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DOI：
10.1111/j.1365-2966.2009.15792.x
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发表时间：
2009-08
影响因子：
4.8
通讯作者：
M. Barkov;S. Komissarov
中科院分区：
文献类型：
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作者：
M. Barkov;S. Komissarov
中微子湮灭机制对质量吸积率的强烈依赖性使得难以解释持续时间超过100秒的长持续时间伽马射线暴（LGRB）以及与主伽马射线脉冲相隔数百秒的前体。更困难的是解释 Swift 对浅衰变阶段和 X 射线耀斑的观测结果，如果它们确实表明中央引擎的活动长达 10 4 秒。这些数据表明，必须考虑一些其他最有可能的磁性机制。由于磁机制的效率不太依赖于质量吸积率，因此磁模型不需要在恒星塌缩的最初几秒钟内形成吸积盘，因此不需要在超新星前（SN）状态下非常快速旋转的恒星核心。这扩大了潜在 LGRB 祖细胞的范围。在本文中，我们重新审视了接近的二元情景，考虑到了塌缩星模型中吸积盘后期发展的可能性，并研究了质量吸积率、黑洞（BH）质量和自旋的可用范围。我们发现 BH 质量可以远高于塌陷星模型中通常假设的 2-3 M ☉ ，并且通常超过 SN 前质量的一半。 BH 自旋相当温和，a = 0.4-0.8，但仍然足够高，只要磁场足够强，Blandford-Znajek 机制就能保持高效。我们的数值模拟证实了磁驱动恒星爆炸的可能性，与之前的研究一致，但指出 BH 地平线上所需的磁通量超过 10 28 G cm 2 。目前我们还不能肯定地回答恒星内部是否能够产生如此强的磁场。也许，与 LGRB 相关的超新星爆炸仍然是中微子驱动的，它们的伽马射线特征是前兆。 SN爆炸清理了磁驱动伽马射线暴（GRB）喷流的逃逸通道，这可能会产生主脉冲。在这种情况下，对磁场强度的要求可以降低。双星起源的一个特别有趣的版本涉及沃尔夫-拉叶星与超紧凑伴星、中子星或 BH 的合并。在这种情况下，我们预计会形成寿命非常长的吸积盘，这可以解释斯威夫特观测到的浅衰变阶段和X射线耀斑。类似地，由于假定 LGRB 祖先的旋转速度异常快，目前的单星模型中预计也会有长寿命的磁力中央发动机。
The strong dependence of the neutrino annihilation mechanism on the mass accretion rate makes it difficult to explain the long-duration gamma-ray bursts (LGRBs) with duration in excess of 100 s as well as the precursors separated from the main gamma-ray pulse by few hundreds of seconds. Even more difficult is to explain the Swift observations of the shallow decay phase and X-ray flares, if they indeed indicate activity of the central engine for as long as 10 4 s. These data suggest that some other, most likely magnetic mechanisms have to be considered. Since the efficiency of magnetic mechanisms does not depend that much on the mass accretion rate, the magnetic models do not require the development of accretion disc within the first few seconds of the stellar collapse and hence do not require very rapidly rotating stellar cores at the pre-supernova (SN) state. This widens the range of potential LGRB progenitors. In this paper, we re-examine the close binary scenario allowing for the possibility of late development of accretion discs in the collapsar model and investigate the available range of mass accretion rates, black hole (BH) masses and spins. We find that the BH mass can be much higher than 2-3 M ☉ , usually assumed in the collapsar model, and normally exceeds half of the pre-SN mass. The BH spin is rather moderate, a = 0.4-0.8, but still high enough for the Blandford-Znajek mechanism to remain efficient provided the magnetic field is sufficiently strong. Our numerical simulations confirm the possibility of magnetically driven stellar explosions, in agreement with previous studies, but point towards the required magnetic flux on the BH horizon in excess of 10 28 G cm 2 . At present, we cannot answer with certainty whether such a strong magnetic field can be generated in the stellar interior. Perhaps, the SN explosions associated with LGRBs are still neutrino-driven and their gamma-ray signature is the precursors. The SN blast clears up escape channels for the magnetically driven gamma-ray burst (GRB) jets, which may produce the main pulse. In this scenario, the requirements on the magnetic field strength can be lowered. A particularly interesting version of the binary progenitor involves merger of a Wolf-Rayet star with an ultracompact companion, neutron star or BH. In this case, we expect the formation of very long-lived accretion discs, that may explain the phase of shallow decay and X-ray flares observed by Swift. Similarly long-lived magnetic central engines are expected in the current single star models of LGRB progenitors due to their assumed exceptionally fast rotation.