Birds of a Feather: A Statistical Search for X-ray Pulsars in Supernova Remnant Fields

The search for X-ray pulsars is often limited by a lack of photons or insufficient timing resolution. In these cases, we would like to identify pulsar candidates based on their spectral signature. Here we attempt to categorize unidentified ASCA X-ray point sources according to the statistics of a collection of previously identified objects with similar spectral characteristics. We define our sample to be those sources located inside the Galactic plane (|b| < 5.0 degrees), detected at >5 sigma, and found in the same GIS field as a known supernova remnant. Filtering this collection on the basis of count rates, hardness ratios, power law slopes (where applicable), and the presence of thermal emission lines, we ascertain a statistical idea of the nature of each unknown source. In our preliminary study of 59 objects, we find 14 sources that have higher hardness ratios and are likely to be associated with low mass X-ray binary systems. Of the 44 remaining softer sources, 12 of the 29 known sources are X-ray pulsars, and 13 are identified supernova remnants that currently have not been associated with any pulsars. The unknown objects with the highest degrees of similarity to the known pulsars are the basis of subsequent observations. We acknowledge the support of NASA grant NAG 5-7935.