Synchrotron emission from virial shocks around stacked OVRO-LWA galaxy clusters
Synchrotron emission from virial shocks around stacked OVRO-LWA galaxy clusters
复制标题
堆叠式 OVRO-LWA 星系团周围维里激波产生的同步辐射
DOI：
10.1093/mnras/stad785
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发表时间：
2023
影响因子：
4.8
通讯作者：
Keshet, Uri
中科院分区：
文献类型：
--
作者：
Hou, Kuan-Chou;Hallinan, Gregg;Keshet, Uri
星系团通过大规模、强烈的结构形成冲击来积累质量。这种维里激波被认为会分别在宇宙射线电子（CRE）和磁场中沉积热能的部分 ψe 和 ψB ，从而产生轻子维里环。然而，直到现在还没有令人信服地建立预期的同步加速器信号。我们将来自 OVRO-LWA 的低频无线电数据叠加在 44 个最大的高纬度扩展 MCXC 星团周围，通过将星团重新调整为其特征 R500 半径来增强环灵敏度。高频率 (73MHz) 和共同添加的低频率通道 (36–68MHz) 分别表明在 (2.4–2.6)R500 处出现显着的 (4–5σ) 过量峰值，与先前堆叠的费米γ射线信号一致，该信号被解释为来自维里激波 CRE 的逆康普顿发射。堆叠的无线电信号通过来自较大质量星团的维里激波同步加速器发射很好地拟合（TS测试：高频4-6σ，低频4-8σ，以及8-10σ联合），其中， 是质量星团的无量纲吸积率，并且是哈勃常数H。推断的 CRE 谱指数平坦，p≃ 2.0 ± 0.2，与强冲击中的加速度一致。假设均分或使用从费米信号产率推断，对应于典型维里激波下游的 B≃ (0.1–0.3)G 磁场。初步证据表明非球形冲击，具有 2-3 倍的伸长。
Galaxy clusters accrete mass through large-scale, strong, structure-formation shocks. Such a virial shock is thought to deposit fractions ξeand ξBof 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,R500radii. Both high (73 MHz) and co-added low (36–68 MHz) frequency channels separately indicate a significant (4–5σ) excess peaked at (2.4–2.6)R500, coincident with a previously stackedFermiγ-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, whereis the dimensionless accretion rate for a cluster of massMand a Hubble constantH. The inferred CRE spectral index is flat,p≃ 2.0 ± 0.2, consistent with acceleration in a strong shock. Assuming equipartition or usinginferred from theFermisignal yields, corresponding toB≃ (0.1–0.3)G magnetic fields downstream of typical virial shocks. Preliminary evidence suggests non-spherical shocks, with factor 2–3 elongations.