2025ApJ...992..113W

Pulsar scintillation serves as a valuable tool for investigating interstellar scattering screens and their properties. In this paper, we report on multiepoch interstellar scintillation from the millisecond pulsar B1937+21 (J1939+2134) using Five-hundred-meter Aperture Spherical radio Telescope (FAST) observations at 1250 MHz with 500 MHz bandwidth. The diffractive scintillation properties are investigated for an observing baseline of 3 yr. The scintillation timescale, exponential index, and decorrelation bandwidth are determined to be 7.67 ± 1.61 minutes, 1.54 ± 0.09, and 0.56 ± 0.25 MHz, respectively, from the autocorrelation functions of the dynamic spectra. These scintillation parameters are found to vary temporally. The frequency dependencies of scintillation parameters exhibit single-power spectral behaviors; however, the derived spectral indices deviate from the theoretical Kolmogorov spectrum. The fringe pattern that forms from interference of scattered waves is revealed in the secondary spectrum as a parabolic arc with a well-determined curvature of 0.95 ± 0.50 s³. The parabolic arc is present contemporaneously over a wide frequency range and scales with frequency as a power law with an index of -0.80 ± 0.18, indicating the broadband nature of the scintillation arc. The arc curvature exhibits annual variation and is well approximated by a one-dimensional scattering screen located approximately 95% of the distance toward the pulsar. These findings will contribute to a deeper understanding of the underlying physics of the ionized interstellar medium.