论文标题
从堆叠的OVRO-LWA星系簇周围的病毒冲击中发出的同步支出
Synchrotron emission from virial shocks around stacked OVRO-LWA galaxy clusters
论文作者
论文摘要
星系簇通过大规模，强，结构形成冲击的质量增生。这种病毒冲击被认为可以分别沉积$ξ_e$和$ξ_b$在宇宙射线电子（CRES）和磁场中的$ξ_b$，从而产生了松弛的病毒环。但是，到目前为止，还没有令人信服地建立预期的同步加速器信号。我们在44个最大，高纬度，扩展的MCXC群集周围堆叠了来自OVRO-LWA的低频无线电数据，从而通过将簇重新缩放到其特征性的$ r_ {500} $ radii来增强了环灵敏度。高（73 MHz）和共同添加的低（$ 36 \ text { - } 68 \ text {MHz} $）频率单独指示一个重要的（$ 4 \ text { - }5σ$）超过$（2.4 \ text { - } 2.6）2.6）r_ {500} $，以前的$（2.4）病毒震动CRES的逆孔子发射。堆叠的无线电信号非常合适（TS测试：$ 4 $ - $6σ$高频时，低频时$ 4 $ - $8σ$，$ 8 $ - $10σ$ not）通过Virial-shock Synchrotron从更大的群集中排放出来10^{ - 4} $，其中$ \ dot {m} \ equiv \ dot {m}/（mh）$是质量$ $ m $和哈勃常数$ h $的无尺寸积聚率。推断的CRE光谱指数是平坦的，$ p \ simeq 2.0 \ pm 0.2 $，与强烈冲击的加速一致。 Assuming equipartition or using $\dot{m}ξ_e\sim0.6\%$ inferred from the Fermi signal yields $ξ_B\simeq (2\text{--}9)\%$, corresponding to $B \simeq (0.1\text{--}0.3)~μ\text{G}$ magnetic fields downstream of typical virial shocks.初步证据表明非球形冲击，因子$ 2 $ - $ 3 $伸长率。
Galaxy clusters accrete mass through large scale, strong, structure-formation shocks. Such a virial shock is thought to deposit fractions $ξ_e$ and $ξ_B$ of the thermal energy in cosmic-ray electrons (CREs) and magnetic fields, respectively, thus generating a leptonic virial ring. However, the expected synchrotron signal was not convincingly established until now. We stack low-frequency radio data from the OVRO-LWA around the 44 most massive, high latitude, extended MCXC clusters, enhancing the ring sensitivity by rescaling clusters to their characteristic, $R_{500}$ radii. Both high (73 MHz) and co-added low ($36\text{--}68\text{ MHz}$) frequency channels separately indicate a significant ($4\text{--}5σ$) excess peaked at $(2.4 \text{--} 2.6) R_{500}$, coincident with a previously stacked Fermi $γ$-ray signal interpreted as inverse-Compton emission from virial-shock CREs. The stacked radio signal is well fit (TS-test: $4$--$6σ$ at high frequency, $4$--$8σ$ at low frequencies, and $8$--$10σ$ joint) by virial-shock synchrotron emission from the more massive clusters, with $\dot{m}ξ_eξ_B\simeq (1\text{--}4)\times 10^{-4}$, where $\dot{m}\equiv \dot{M}/(MH)$ is the dimensionless accretion rate for a cluster of mass $M$ and a Hubble constant $H$. The inferred CRE spectral index is flat, $p \simeq 2.0 \pm 0.2$, consistent with acceleration in a strong shock. Assuming equipartition or using $\dot{m}ξ_e\sim0.6\%$ inferred from the Fermi signal yields $ξ_B\simeq (2\text{--}9)\%$, corresponding to $B \simeq (0.1\text{--}0.3)~μ\text{G}$ magnetic fields downstream of typical virial shocks. Preliminary evidence suggests non-spherical shocks, with factor $2$--$3$ elongations.
