FAST Scintillation Data Place PSR B1257+12 Scattering Screens at 166-354 pc

The team recorded 31 sessions of at least 30 minutes and performed one-dimensional autocorrelation and secondary-spectrum analysis on the 14 longest tracks. Inner, middle and outer arcs appear simultaneously in three epochs. Annual modulation of the inner-arc curvature fixes an isotropic screen at 233 pc with transverse velocity components -7.2 and -41.1 km s^{-1}. Delay-profile slopes for the middle and outer arcs remain at or below the Kolmogorov index.

These distances imply that the measured DM variations arise from plasma well outside the 1-au scale of the known planets. The outer arc shows a low DM-change rate and no evidence for a screen inside ~100 pc, consistent with a relatively clean local environment around the pulsar. Earlier timing campaigns had already limited any dense circumpulsar material; the scintillation results now place quantitative upper bounds on undetected nearby turbulence.

The absence of a detectable nearby screen does not yet exclude faint structures that would require longer integrations or higher sensitivity. Future FAST or SKA monitoring campaigns spanning multiple years could test whether weak inner screens emerge or whether the local medium remains truly evacuated. Such data would also refine the transverse velocity vector and test whether the screens are static or evolving.

Comparison with the 1992 discovery paper and subsequent timing solutions shows that the new scintillation distances align with the low DM gradient already inferred from two decades of pulse-arrival measurements, strengthening the case that the planets orbit in a low-density bubble.