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Session 107 - The Galactic Center & Bulge.
Display session, Saturday, January 10
Exhibit Hall,

[107.01] A VLA Survey for Radio Pulsars in and Beyond the Galactic Center

T. J. W. Lazio (NRL, NRC), J. M. Cordes (Cornell,NAIC), N. E. Kassim (NRL), Z. Arzoumanian (Cornell)

Only 15 radio pulsars of the current catalog of approximately 750 are within 5^\circ of Sgr A and none are within 1^\circ. This deficit is due to interstellar scattering so severe as to smear together individual pulses. Pulse broadening for pulsars in the Galactic center (GC) is 350\,\nu_GHz^-4 seconds\/ for a radio frequency of \nu_GHz GHz. Pulsars beyond---but viewed through---the GC suffer even greater pulse broadening. Periodicity searches at radio frequencies will be successful only at \nu > 5 GHz, and will find only long-period pulsars.

In order to find GC pulsars, we are employing an alternate strategy---an aperture synthesis survey. Our survey is far more sensitive than a periodicity search because angular broadening of compact GC sources does not desensitize the survey. The scattering diameter of Sgr A^* is 1.\!\!^\prime\prime3\,\nu_GHz^-2; OH/IR stars within 25^\prime of Sgr A^* have comparable diameters. The predicted scattering diameter of a compact GC source is 0.\!\!^\prime\prime7 at 1.4 GHz and 12^\prime\prime at 0.33 GHz. These scattering diameters are well-matched to the synthesized beam of the A-configuration VLA: 1.\!\!^\prime\prime2 and 6^\prime\prime, respectively.

Our objective is to find compact, steep-spectrum, polarized sources. We surveyed the inner 1^\circ of the GC at 0.33 and 1.4 GHz with the \hboxVLA. The observation wavelengths are matched to the typical pulsar spectrum which peaks at \nu < 1 GHz. The 1.4 GHz observations were sensitive to cross-polarized emission and are being used to identify linearly-polarized objects. The angular extent of the survey is slightly larger than the extent of the hyperstrong scattering region responsible for the angular broadening of Sgr A^* and the OH/IR stars.

The number of detectable\/ pulsars in the inner 1^\circ (= 150 pc at 8.5 kpc) of the GC may range from 1 to 100, with the larger values resulting from recent, vigorous starbursts. We present our current catalog, which contains 75 objects. We have begun a program of near-IR observations on the Palomar 5 m telescope to aid in the identification of these sources. Our 0.33 GHz observations will also be used in conjunction with a series of 0.33 GHz observations obtained over the past 6 yr to search for radio transients.

Basic research in radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research. TJWL is supported by an NRC-NRL Research Associateship.

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