Uncovering the Galactic Center Pulsar Population: Discovery of Two Highly Dispersed Radio Pulsars Near Sgr A*

A cluster composed mainly of young massive stars has been shown to exist around Sgr A*, the supermassive black hole at the center of our Galaxy [1]. With respect to probing the ionized gas and gravitational properties of the region, the presence of such a cluster is doubly advantageous when we consider that massive stars are neutron star (NS) progenitors and therefore there must be a numerous NS population near Sgr A * as well. This leads to the conclusion that a sizable fraction of the NSs would be active radio pulsars, and Pfahl & Loeb [2] estimate that there are ~100-1000 active pulsars with orbital periods around Sgr A * of less than 100 years. Lazio & Cordes [3] show that there is a scattering screen of ionized gas towards Sgr A * that makes pulsars in tight orbits around the central black hole increasingly hard to detect, but that some of these pulsars will remain detectable at the distance of the Galactic Center even at the high frequencies needed to mitigate pulse broadening from scattering. Moreover, Lazio et al. [4] show that the scattering screen likely has gaps, meaning that highly dispersed pulsars may be closer to Sgr A * than the current NE2001 model suggests [5]. Of the ~1700 pulsars presently known, only two are within 1 degrees of Sgr A*. J1746-2856 and J1745-2912, with dispersion measures (DMs) of 1168 and 1130 pc/cc respectively, were discovered only recently by Johnston et al. [6] with the Parkes telescope. While high, their DMs are not consistent with them being beyond the scattering screen or even beyond the Galaxy's molecular ring. Their distances from Sgr A * are likely to be at leas