Pulse Morphology of the Galactic Center Magnetar PSR J1745–2900

We present results from observations of the Galactic Center magnetar, PSR J1745–2900, at 2.3 and 8.4 GHz with the NASA Deep Space Network 70 m antenna, DSS-43. We study the magnetar's radio profile shape, flux density, radio spectrum, and single pulse behavior over a ~1 year period between MJDs 57233 and 57621. In particular, the magnetar exhibits a significantly negative average spectral index of ⟨α⟩ = -1.86 ± 0.02 when the 8.4 GHz profile is single-peaked, which flattens considerably when the profile is double-peaked. We have carried out an analysis of single pulses at 8.4 GHz on MJD 57479 and find that giant pulses and pulses with multiple emission components are emitted during a significant number of rotations. The resulting single pulse flux density distribution is incompatible with a log-normal distribution. The typical pulse width of the components is ~1.8 ms, and the prevailing delay time between successive components is ~7.7 ms. Many of the single pulse emission components show significant frequency structure over bandwidths of ~100 MHz, which we believe is the first observation of such behavior from a radio magnetar. We report a characteristic single pulse broadening timescale of ⟨τ_d⟩ = 6.9 ± 0.2 at 8.4 GHz. We find that the pulse broadening is highly variable between emission components and cannot be explained by a thin scattering screen at distances ≳1 kpc. We discuss possible intrinsic and extrinsic mechanisms for the magnetar's emission and compare our results to other magnetars, high magnetic field pulsars, and fast radio bursts