The Angular Broadening of the Galactic Center Pulsar SGR J1745-29: A New Constraint on the Scattering Medium

The pulsed radio emission from the Galactic Center (GC) magnetar SGR J1745-29 probes the turbulent, magnetized plasma of the GC hyperstrong scattering screen through both angular and temporal broadening. We present the first measurements of the angular size of SGR J1745-29, obtained with the Very Long Baseline Array and the phased Very Large Array at 8.7 and 15.4 GHz. The source sizes are consistent with the scatter–broadened size of Sagittarius A* at each frequency, demonstrating that SGR J1745-29 is also located behind the same hyperstrong scattering medium. Combining the angular broadening with temporal scattering obtained from pulsar observations provides a complete picture of the scattering properties. If the scattering occurs in a thin screen, then it must be at a distance ∆ ∼ 5 kpc. A best-fit solution for the distance of a thin screen is ∆ = 5.9±0.3 kpc, consistent with being located in the Scutum spiral arm. This is a substantial revision of the previously held model in which the scattering screen is located very close to the GC. As also discussed in Spitler et al. (2013), these results suggest that GC searches can detect millisecond pulsars gravitationally bound to Sgr A* with observations at ∼ 10 GHz and ordinary pulsars at even lower frequencies. Subject headings: pulsars: general, pulsars: individual(SGR J1745-29), black hole physics, scattering Astronomy Department and Radio Astronomy Laboratory, University of California, Berkeley, 601 Campbell Hall #3411, Berkeley, CA 94720, USA; [email protected] ASTRON, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands NRAO,520 Edgemont Road, Charlottesville, VA 22903-2475 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands