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arXiv 1012.0001astro-ph.HE
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伽马射线暴的原磁星模型

The Proto-Magnetar Model for Gamma-Ray Bursts

B. D. Metzger, D. Giannios, T. A. Thompson, N. Bucciantini, E. Quataert

摘要:

长持续时间的伽马射线暴(GRB)起源于大质量恒星的核心坍缩,但中心引擎的身份仍然难以捉摸。先前的工作表明,快速旋转的强磁化原中子星(“毫秒原磁星”)产生的外流具有与产生长伽玛暴所需的能量、时间尺度和磁化强度σ_0(最大洛伦兹因子)一致的能量、时间尺度和磁化强度σ_0。在这里,我们扩展这项工作,以构建一个自洽的模型,直接连接到所观察到的即时排放的中央引擎的属性。就在超新星冲击波发射后,一股由中微子加热的风从原磁星中喷出。流出物通过与恒星的相互作用被准直成双极喷流。当磁星冷却时,磁星风变成极端相对论性的,坡印廷通量占主导地位(σ_0>> 1),其时间尺度与喷流穿过恒星清除空腔所需的时间相当。虽然即时发射的网站和机制是有争议的,我们计算了两个模型预测的发射:磁耗散和内部冲击。我们的研究结果有利于磁耗散模型的一部分,因为它预测一个相对恒定的“带”谱峰能量E_peak随时间的伽玛暴。当t ~ 10-100秒时,当中子星对中微子透明时,喷流重子负载突然减小。具有超高磁化强度的射流不能有效地加速和耗散它们的能量,这表明这种转变结束了即时发射,并可以解释随后的陡峭衰减阶段。我们评估了几种可能与磁星诞生有关的现象,包括低光度GRB,富热GRB/X射线闪光,非常明亮的超新星,和持续时间短的GRB与延长发射。

英文摘要:

Long duration Gamma-Ray Bursts (GRBs) originate from the core collapse of massive stars, but the identity of the central engine remains elusive. Previous work has shown that rapidly spinning, strongly magnetized proto-neutron stars (`millisecond proto-magnetars') produce outflows with energies, timescales, and magnetizations sigma_0 (maximum Lorentz factor) that are consistent with those required to produce long GRBs. Here we extend this work in order to construct a self-consistent model that directly connects the properties of the central engine to the observed prompt emission. Just after the launch of the supernova shock, a wind heated by neutrinos is driven from the proto-magnetar. The outflow is collimated into a bipolar jet by its interaction with the star. As the magnetar cools, the wind becomes ultra-relativistic and Poynting-flux dominated (sigma_0 >> 1) on a timescale comparable to that required for the jet to clear a cavity through the star. Although the site and mechanism of the prompt emission are debated, we calculate the emission predicted by two models: magnetic dissipation and internal shocks. Our results favor the magnetic dissipation model in part because it predicts a relatively constant `Band' spectral peak energy E_peak with time during the GRB. The jet baryon loading decreases abruptly when the neutron star becomes transparent to neutrinos at t ~ 10-100 seconds. Jets with ultra-high magnetization cannot effectively accelerate and dissipate their energy, suggesting this transition ends the prompt emission and may explain the steep decay phase that follows. We assess several phenomena potentially related to magnetar birth, including low luminosity GRBs, thermal-rich GRBs/X-ray Flashes, very luminous supernovae, and short duration GRBs with extended emission.

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