HYPERSTRONG RADIOWAVE SCATTERING IN THE GALACTIC-CENTER - I - A SURVEY FOR EXTRAGALACTIC SOURCES SEEN THROUGH THE GALACTIC-CENTER

The scattering diameters of Sgr A and several nearby OH masers (appro ximate to 1'' at 1 GHz) indicate that a region of enhanced scattering is along the line of sight to the Galactic center (GC). The scattering diameter of an extragalactic source seen through this scattering regi on will be larger by the ratio of the Sun-GC distance to the GC-scatte ring region separation. This ratio could be a factor of a few, if the scattering region is far from the GC and only a random superposition w ith it, to more than 100, if the scattering region is within the GC. W e have used the VLA to survey 10 (11) fields at 20 cm (6 cm) that are between 7' and 137' from Sgr A. Our objective was to identify extraga lactic sources and measure their scattering diameters so as to constra in the GC-scattering region separation. In order to find sources withi n these fields, we have employed pdfCLEAN, a source detection algorith m in which sources are identified in an image by comparing the intensi ty histogram of the image to that expected from a noise-only image. We found over 100 sources, with the faintest sources being approximately 3 mJy. The average number of sources per field is approximately 10, t hough fields close to Sgr A tend to contain fewer sources. In a compa nion paper we combine our survey with previous observations of the GC, and we assess the likelihood that the scattering region is so close t o the GC that the resulting scattering diameters cause extragalactic s ources to be resolved out by our observations. A number of Galactic so urces ale included in our source catalog. We discuss the double-lobed source 1LC 359.872 + 0.178, potentially an X-ray quiet version of 1E 1 740.7 - 2942, a shell-like structure with a central point source, and a possible radio transient.