Author(s): A.B. Pearlman, W.A. Majid, T.A. Prince, J. Kocz, Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, California, UNITED STATES|W.A. Majid, T.A. Prince, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, UNITED STATES|S. Horiuchi, CSIRO Astronomy and Space Science, Canberra Deep Space Communications Complex, Tuggeranong, Australian Capital Territory, AUSTRALIA|
Institution(s): 1. Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA, United States. 2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States. 3. CSIRO Astronomy and Space Science, Canberra Deep Space Communications Complex, Tuggeranong, ACT, Australia.
Contributing team(s): (none)
The Galactic Center magnetar, PSR J1745-2900, lies at a projected distance of ~0.1 pc from Sgr A* and serves as an excellent probe of the magneto-ionic environment near the Galaxy's central black hole. We present results from simultaneous radio observations of the magnetar at 2.3 and 8.4 GHz with the NASA Deep Space Network 70 m antenna, DSS-43, in Tidbinbilla, Australia. We characterize the magnetar's pulse profile shape, flux density, radio spectrum, and single pulse behavior over a ~1 year period between MJDs 57233 and 57621. When the 8.4 GHz profile is single-peaked, the magnetar exhibits an average spectral index of 〈α〉 = -1.86 ± 0.02 between 2.3 and 8.4 GHz, which is comparable to the mean spectral index of ordinary radio pulsars. The radio spectrum significantly flattens when the pulse profile becomes double-peaked. This behavior is atypical of most radio magnetars, which have relatively flat or inverted radio spectra. From an analysis of single pulses at 8.4 GHz on MJD 57479, we find that giant pulses and pulses with multiple emission components are emitted during a significant number of rotations. The single pulse flux density distribution cannot be described by a log-normal distribution due to these giant pulses. The intrinsic pulse width of the components is typically ~1.8 ms, and the prevailing delay time between successive components is ~7.7 ms. Many of the single pulse emission components display frequency structure over bandwidths of ~100 MHz, which is the first observation of such behavior from a radio magnetar. We measure a characteristic single pulse broadening timescale of τd = 6.9 ± 0.2 ms at 8.4 GHz, which is more than an order of magnitude larger than expected based on previous multi-frequency scattering measurements. We also find that the pulse broadening is extremely variable between emission components and cannot be explained by a static thin scattering screen at distances > ~1 kpc from the magnetar. We will discuss potential intrinsic and extrinsic mechanisms for the magnetar's emission and compare our results to other magnetars, high magnetic field pulsars, and fast radio bursts.