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arXiv 2109.04828astro-ph.HE
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致密星周环境中年轻超新星遗迹的非热发射

Non-thermal emission from young supernova remnants in dense circumstellar environments

Robert Brose, Jonathan Mackey, Iurii Sushch

摘要:

已知超新星遗迹会加速宇宙射线(CR),因为它们会发射非热的无线电波、X射线和伽马射线。然而,将CR加速到PeV能量的能力尚未得到证明。在几个年轻的SNRs的伽马射线光谱中存在截止点,这导致了PeV能量可能只在遗迹演化的最初阶段才能达到的想法。我们使用时间相关的加速代码RATPaC来研究宇宙射线在超新星扩展到大质量恒星周围的密集环境中的加速,在那里丰富的目标材料可能提供一条路径,通过当前和未来的实验来检测伽马射线。我们进行了球对称的1-D模拟,其中我们同时解决传输方程的宇宙射线,磁湍流,和流体力学流动的热等离子体在测试粒子的限制。研究了红超巨星(RSG)和亮蓝变星(LBV)周围自由膨胀风中星周介质(CSM)的典型参数。最大可实现的能量可能仅限于子PeV的能量,尽管靠近祖星的强磁场通过级联增强了连续性阻尼:我们发现最大CR能量为100-200 TeV,在爆炸后一个月内达到。在GeV(TeV)能量下,LBV前身的峰值亮度为1 e43 erg/s(1 e42 erg/s),而RSG前身的峰值亮度为1 e41 erg/s(1 e40 erg/s)。所有计算出的SN在<1个月后达到它们的伽马射线亮度峰值,然后只要SN激波保持在祖先的自由膨胀风中,就以~1/t的速率衰减。在爆炸进入自由膨胀的风后的几周到几个月,费米-LAT波段可能会出现潜在的可检测的伽马射线信号。

英文摘要:

Supernova remnants are known to accelerate cosmic rays (CRs) on account of their non-thermal emission of radio waves, X-rays, and gamma rays. However, the ability to accelerate CRs up to PeV-energies has yet to be demonstrated. The presence of cut-offs in the gamma-ray spectra of several young SNRs led to the idea that PeV energies might only be achieved during the very initial stages of a remnant's evolution. We use the time-dependent acceleration code RATPaC to study the acceleration of cosmic rays in supernovae expanding into dense environments around massive stars, where the plentiful target material might offer a path to the detection of gamma-rays by current and future experiments. We performed spherically symmetric 1-D simulations in which we simultaneously solve the transport equations for cosmic rays, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in the test-particle limit. We investigated typical parameters of the circumstellar medium (CSM) in the freely expanding winds around red supergiant (RSG) and luminous blue variable (LBV) stars. The maximum achievable energy might be limited to sub-PeV energies despite strong magnetic fields close to the progenitor star that enhance turbulence-damping by cascading: we find a maximum CR energy of 100-200 TeV, reached within one month after explosion. The peak luminosity for a LBV progenitor is 1e43 erg/s (1e42 erg/s) at GeV (TeV) energies and, for a RSG progenitor, 1e41 erg/s (1e40 erg/s). All calculated SNe reach their peak gamma-ray luminosity after <~1 month and then fade at a rate ~1/t as long as the SN shock remains in the freely expanding wind of the progenitor. Potentially detectable gamma-ray signals can be expected in the Fermi-LAT waveband weeks to months after an explosion into a freely expanding wind.

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