Green Bank Telescope and Swift X-ray Telescope Observations of the Galactic Center Radio Magnetar SGR J1745-2900

摘要

We present results from eight months of Green Bank Telescope 8.7-GHzobservations and nearly 18 months Swift X-ray telescope observations of theradio magnetar SGR J1745-2900, which is located 2.4" from Sgr A*. We trackedthe magnetar's radio flux density, polarization properties, pulse profileevolution, rotation, and single-pulse behavior. We identified two main periodsof activity in SGR J1745-2900. The first is characterized by approximately 5.5months of relatively stable evolution in radio flux density, rotation, andprofile shape, while in the second these properties varied substantially.Specifically, a third profile component emerged and the radio flux increased onaverage, but also became more variable. Bright single pulses are visible andare well described by a log-normal energy distribution at low to moderateenergies, but with an excess at high energies. The 2-10 keV flux has decayedsteadily since the initial X-ray outburst, in contrast with the radio flux. Ourtiming analysis includes Green Bank Telescope, Swift, and NuSTAR data. When weinclude the X-ray data in our analyses, we find that SGR J1745-2900 exhibited alevel of timing noise unprecedented in a radio magnetar, though an analysis ofonly the radio data indicates timing noise at a level similar to that observedin other radio magnetars. We conclude that, while SGR J1745-2900 is similar toother radio magnetars in many regards, it differs by having experienced aperiod of relative stability in the radio band that now appears to have ended,while the X-ray properties have evolved independently.