Swift J1818.0-1607 discovered in early 2020 is not only the fifth magnetar known with periodic radio pulsations but also the fastest rotating one. Simultaneous 2.25/8.60 GHz observations of Swift J1818.0-1607 were carried out with Shanghai Tian Ma Radio Telescope (TMRT) from MJD 58936 to 59092. The spin-frequency nu and first-order derivative of this magnetar were obtained with piecewise fitting method because of its instable timing properties. We found that the amplitude of short-term fluctuations decreased with time, and the long-term declining trend of nu discovered previously continued in our observations. The best fit long-term were about using our observation data spanning 156 d. The derived characteristic age was about 522 yr, supporting the recent viewpoint that this magnetar may be older than initially thought shortly after its discovery. The flux density of this magnetar was increased at both 2.25 and 8.60 GHz during our observations, and its radio spectrum became flatter at the same time. We also detected bright-quiet type emission mode switching in Swift J1818.0-1607.

stars: magnetars; stars: neutron; pulsars: individual: Swift J1818.0-1607

Shanghai Astronomical Observatory, Chinese Academy of Sciences