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arXiv 2403.18484astro-ph.HEastro-ph.SR
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OB星恒星风泡作为银河系宇宙射线再加速器

Stellar wind bubbles of OB stars as Galactic cosmic-ray re-accelerators

Dominique M. -A. Meyer

AI总结:

本研究通过一维磁流体动力学模拟发现OB星恒星风泡前向激波可再加速银河系宇宙射线,使发射通量增加5倍,强子辐射占主导,为kappa Ori周围增强强子发射提供解释。

摘要:

宇宙射线是在磁化等离子体中传播的高能信使,可能在天体物理激波处被加速,但这并非唯一来源。在呈现激波的各种天体物理对象中,围绕超大质量恒星形成的巨大星周恒星风泡是潜在的非热辐射体。我们展示了对一颗单一OB型主序60 Mo恒星演化磁化环境的一维磁流体动力学模拟,并对该模拟进行后处理以计算银河系宇宙射线背景中既有非热粒子的再加速。研究发现,此类星周泡的前向激波在其膨胀的早期阶段(1 Myr)可作为既有星际宇宙射线的实质性再加速器。这导致超出发射通量增加5倍,其中通过pion0衰变产生伽马射线的强子成分比同步辐射和逆康普顿辐射机制更为重要。我们提出该效应普遍存在于大质量恒星的星周环境中,并推测其他星云(如逃逸大质量恒星的恒星风弓形激波)也充当银河系宇宙射线再加速器。特别是,本研究支持将kappa Ori周围测得的增强强子发射通量解释为源于其风泡前向激波对既有粒子的加速。

英文摘要:

Cosmic rays are highly energetic messengers propagating in magnetized plasma, which are, possibly but not exclusively, accelerated at astrophysical shocks. Amongst the variety of astrophysical objects presenting shocks, the huge circumstellar stellar wind bubbles forming around very massive stars, are potential non thermal emitters. We present the 1D magnetohydrodynamical simulation of the evolving magnetized surroundings of a single, OB type main sequence 60 Mo star, which is post processed to calculate the re-acceleration of preexisting non-thermal particles of the Galactic cosmic ray background. It is found that the forward shock of such circumstellar bubble can, during the early phase (1 Myr) of its expansion, act as a substantial reaccelerator of pre existing interstellar cosmic rays. This results in an increasing excess emission flux by a factor of 5, the hadronic component producing gamma-rays by pion0 decay being more important than those by synchrotron and inverse Compton radiation mechanisms. We propose that this effect is at work in the circumstellar environments of massive stars in general and we conjecture that other nebulae such as the stellar wind bow shocks of runaway massive stars also act as Galactic cosmic-ray re-accelerators. Particularly, this study supports the interpretation of the enhanced hadronic emission flux measured from the surroundings of kappa Ori as originating from the acceleration of pre-existing particles at the forward shock of its wind bubble.

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