A SEARCH FOR THE X-RAY COUNTERPART OF THE UNIDENTIFIED γ-RAY SOURCE 3EG J2020+4017 (2CG078+2)

摘要

We report observations with the Chandra X-Ray Observatory of a field in the γ-Cygni supernova remnant (SNR 78.2+2.1) centered on the cataloged location of the unidentified, bright γ-ray source 3 EG J2020+4017. In this search for an X-ray counterpart to the γ-ray source, we detected 30 X-ray sources. Of these, we found 17 strong-candidate counterparts in optical (visible through near-infrared) cataloged and an additional three through our optical observations. Based on colors and (for several objects) optical spectra, nearly all the optically identified objects appear to be reddened main-sequence stars: none of the X-ray sources with an optical counterpart is a plausible X-ray counterpart to 3EG J2020+4017—if that γ-ray source is a spin-powered pulsar. Many of the 10 X-ray sources lacking optical counterparts are likely (extragalactic) active galactic nuclei, based on the sky density of such sources. Although one of the 10 optically unidentified X-ray sources could be the γ-ray source, there is no auxiliary evidence supporting such an identification.