磁刚度揭示SS433中的拍电子伏特加速器（PeVatron）加速区域
Magnetic rigidity reveals the PeVatron acceleration region in SS 433
AI总结：
本研究通过VLBA观测确定SS433内喷流的磁场轮廓，发现数百AU尺度区域可将质子加速至约2.6PeV，揭示该区域为隐藏的PeVatron加速区。
AI中文摘要：
拍电子伏特加速器（PeVatron）是能将粒子加速至拍电子伏特（PeV）能量的宇宙加速器，近来微类星体喷流成为银河系内PeVatron的有力候选体，SS433尤为典型，因其>100TeV的伽马射线辐射与原子云在空间上重合。然而，喷流内PeV质子被加速并注入的精确区域仍未明确。本文利用存档的多频段甚长基线阵列（VLBA）观测，报道了SS433内喷流在数十天文单位（AU）尺度上的磁场轮廓B(H)，其中H为距中心致密天体的距离。研究发现磁场随H以B(H)∝H^(-0.50±0.12)的规律衰减，表明锥形喷流的磁刚度B(H)R_acc随H增大而提升，这意味着希拉斯极限（E_max∝BH）在数百AU尺度上远高于1PeV，该区域极具潜力将质子加速至LHAASO伽马射线能谱推断的E_cut≈2.6PeV能量。这些结果揭示微类星体SS433的重子抛射物中存在一个隐藏的PeVatron，且位于延伸的TeV辐射瓣的上游。
英文摘要：
PeVatrons are cosmic accelerators capable of driving particles to petaelectronvolt (PeV) energies. Recently, microquasar jets have emerged as compelling Galactic PeVatron candidates. This is especially the case for SS 433 as its $>100$ TeV gamma-ray emission is spatially coincident with an atomic cloud. However, the exact region where PeV protons are accelerated and injected within these jets remains unresolved. Here we report, using archival, multi-frequency VLBA observations, the magnetic field profile $B(H)$ along the SS 433 inner jet on tens of AU scale, where $H$ is the distance from the central compact object. We find that the field declines as $B(H) \propto H^{-0.50\pm0.12}$, demonstrating that the magnetic rigidity $B(H)R_{\rm acc}$ grows with $H$ for a conical jet. This implies the Hillas limit ($E_{\rm max} \propto BH$) to lie well beyond a PeV at a few hundred-AU scale, which becomes a highly potential site for accelerating protons to energies $E_{\rm cut} \simeq 2.6$ PeV inferred from the LHAASO gamma-ray spectrum. These results reveal a hidden PeVatron within the baryonic ejecta of microquasar SS 433, well upstream of the extended TeV-emitting lobes.
