arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1502.02780astro-ph.HE
收藏

星系团外围弱球形激波的射电辐射

Radio emission from weak spherical shocks in the outskirts of galaxy clusters

Hyesung Kang

摘要:

在Kang(2015)中,我们计算了宇宙射线电子的加速和随后在弱球形冲击下的射电同步辐射,这些冲击预计将在星系团的外围形成。在那里,我们证明了,在减速球形冲击下,电子和辐射的体积积分光谱显著偏离恒定平面冲击预测的测试粒子幂律,因为冲击压缩比和注入电子的通量随时间减小。在这项研究中,我们考虑球形爆炸波传播到一个恒定的密度核心所包围的等温晕密度下降的轮廓,以探讨如何减速率的冲击波速度的影响,从加速电子的无线电发射。通过假设球壳上的带状激波表面和相关的相对论电子下游区域,计算了模型激波的表面亮度剖面和体积积分射电谱。当激波后磁场强度约为7微高斯时,在5000万年左右的激波年龄,体积分射电谱逐渐变陡,谱指数在0.1 ~ 10 GHz范围内从alpha_{inj}到alpha_{inj} +0.5,其中alpha_{inj}是根据扩散激波加速理论所预期的激波位置处的注入指数。这种逐渐变陡可以解释星团A2266中射电遗迹的弯曲射电频谱,如果遗迹激波足够年轻,以至于断裂频率落在1 GHz左右,那么Trasatti等人(2014)将其解释为幂律断裂。

英文摘要:

In Kang (2015) we calculated the acceleration of cosmic-ray electrons and the ensuing radio synchrotron emission at weak spherical shocks that are expected to form in the outskirts of galaxy clusters.There we demonstrated that, at decelerating spherical shocks, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws predicted for constant planar shocks, because the shock compression ratio and the flux of injected electrons decrease in time. In this study, we consider spherical blast waves propagating into a constant density core surrounded by an isothermal halo with a decreasing density profile in order to explore how the deceleration rate of the shock speed affects the radio emission from accelerated electrons. The surface brightness profile and the volume-integrated radio spectrum of the model shocks are calculated by assuming a ribbon-like shock surface on a spherical shell and the associated downstream region of relativistic electrons. If the postshock magnetic field strength is about 7 microgauss, at the shock age of ~50 Myr, the volume-integrated radio spectrum steepens gradually with the spectral index from alpha_{inj} to alpha_{inj}+0.5 over 0.1-10 GHz, where alpha_{inj} is the injection index at the shock positionexpected from the diffusive shock acceleration theory. Such gradual steepening could explain the curved radio spectrum of the radio relic in cluster A2266, which was interpreted as a broken power-law by Trasatti et al. (2014), if the relic shock is young enough so that the break frequency falls in around 1 GHz.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑