两颗新的高度散射的快速射电暴：源自源周介质散射展宽的证据
Two new highly scattered fast radio bursts: evidence for scatter broadening by the circumsource medium
中文总结 AI 辅助
本研究在CRACO后端调试中发现两颗高度散射FRB，其中FRB 240312D的散射仅可能来自源周介质，还计算了符合短FRB的发生率，表明强散射与FRB源存在因果关联。
中文摘要 AI 辅助
我们在 Commensal Realtime ASKAP Fast Transient COherent（CRACO， commensal实时ASKAP快速瞬变相干后端）调试期间发现了两颗高度散射的快速射电暴（Fast Radio Bursts，FRBs）。FRB 240210D和FRB 240312D在归算至1 GHz时的散射时标分别为$34\pm6$毫秒和$300\pm48$毫秒。FRB 240312D起源于一个红移仅为0.05的正面朝向星系的旋臂附近。银河系屏的闪烁对散射屏与源的距离约束为约10秒差距。因此，FRB 240312D是首颗可排除位于宿主星系中心、背景星系或中间结构的散射屏的高度散射FRB，仅剩下源周介质作为散射源。对宿主星系的积分场光谱分析显示，其为一个类银河系星系，FRB位置处存在一个恒星形成区。我们发现脉冲星风星云内的折射散射是最可能的散射起源，但该解释并不完全令人满意，因为它需要精细调谐的取向，因此需要针对不同FRB前身星模型开展额外的理论研究。基于这两颗FRB，我们计算得到总发生率$R_{\mathrm{tot}}=210^{+460}_{-180}$次/（天空平方度·天），其持续时间在55.2毫秒至1秒之间， fluence（能流密度）高于9 Jy·毫秒，与短FRB的发生率一致。这一升高的发生率表明，其他FRB中观测到的强散射同样并非源于偶然对准的视线，而是与FRB源存在因果关联。
英文摘要
We found two highly scattered Fast Radio Bursts (FRBs) during commissioning of the Commensal Realtime ASKAP Fast Transient COherent (CRACO) backend. FRB 240210D and FRB 240312D have scattering times of $34\pm6$ and $300\pm48$ ms, respectively, when scaled to 1 GHz. FRB 240312D originates near a spiral arm of a face-on galaxy at a redshift of only 0.05. Scintillation from a Milky Way screen constrains the distance of the scattering screen to $\sim 10$ pc from the source. FRB 240312D is therefore the first highly scattered FRB where scattering screens in the host galaxy centre, a background galaxy, or intervening structures can all be excluded, leaving only the circumsource medium. Integral field spectroscopy of the host reveals a Milky Way-like galaxy with a star-formation region at the FRB position. We find refractive scattering in a pulsar wind nebula as the most likely scattering origin. However, the explanation is not completely satisfactory as it requires a fine-tuned orientation. Hence, additional theoretical studies under different FRB progenitor models are needed. From the two FRBs, we calculate a total rate of $R_\mathrm{tot}=210^{+460}_{-180}\,\mathrm{events}\,\mathrm{sky}^{-1}\mathrm{day}^{-1}$ with durations between 55.2 ms and 1 s and above a fluence of 9 Jy ms consistent with the rate of shorter FRBs. This elevated rate suggests that the strong scattering seen in other FRBs likewise does not arise from chance-aligned sightlines, but is instead causally linked to the FRB sources.
