2024ApJ...961...48W

We report detection results of nine millisecond pulsars (MSPs) at 8600 MHz using simultaneous 2250 and 8600 MHz observations conducted with the Shanghai Tian Ma Radio Telescope. Mainly benefiting from updated ephemerids with 2250 MHz observations, integrated profiles of all nine MSPs at 8600 MHz are successfully obtained by coherently adding multi-epoch (3-83 epochs) observation data spanning from 19-1210 days, which significantly increases the number of MSPs with published profiles (from 4 to 11) above 8000 MHz, as seven of our target MPSs had no related results previously. Combining our new flux density and pulse width measurements with previous low-frequency results, we study their integrated profile evolution and spectral behaviors in a wider frequency range. We find their component separations and pulse widths remain almost constant, which is consistent with previous findings. While dramatic evolution of integrated profiles exists at low frequencies, we observe a potential end of the related evolution around 5 GHz in eight MSPs. The spectra of four MSPs are found to deviate from a single power law, and we fit them with a broken power law. The change in the profile of PSR J1713+0747, which started around MJD 59320-59321, seems to be more prominent as the observation frequency increases. Compared with the effects of the interstellar medium, we prefer to explain this event as some changes in the magnetosphere. We also find its integrated profile possibly had not recovered to the pre-event state until MJD 59842-59857.