VLA Observations of Single Pulses from the Galactic Center Magnetar

We present results of a 7-12 GHz phased-array study of the Galactic center magnetar J1745-2900 with the Karl G. Jansky Very Large Array (VLA). Using data from two 6.5 hr observations from 2014 September, we find that the average profile is comprised of several distinct components at these epochs and is stable over similar to day timescales and similar to GHz frequencies. Comparison with additional phased VLA data at 8.7 GHz shows significant profile changes on longer timescales. The average profile at 7-12 GHz is dominated by the jitter of relatively narrow pulses. The pulses in each of the four main profile components seen in 2014 September are uncorrelated in phase and amplitude, though there is a small but significant correlation in the occurrence of pulses in two of the profile components. Using the brightest pulses, we measure the dispersion and scattering parameters of J1745-2900. A joint fit of 38 pulses gives a 10 GHz pulse-broadening time of tau(sc,10) = 0.09 +/- 0.03 ms and a dispersion measure of DM = 1760(-1.3)(+2.4) pc cm(-3). Both of these results are consistent with previous measurements, which suggests that the scattering and dispersion measure of J1745-2900 may be stable on timescales of several years.