ASCA observation of a radio-loud quasar and a new candidate for a cluster of galaxies

During an X-ray observation of the distant galaxy cluster CL 0107+31 (z = 0.69) with ASCA, an extended X-ray source was detected in the field of view. Based on an image analysis in two different energy bands of 1-3 keV and 3-10 keV, we found that this source consists of a hard point-like component and an additional soft diffuse X-ray source extended over ≥ 3′ in radius. However, due to poor photon statistics, we could not distinguish whether their X-ray spectra are thermal or non-thermal. The peak position of the central X-ray source coincides with a radio-loud quasar, NRAO 58. NRAO 58 is found to have a power-law spectrum with a photon index 1.6^+0.3_-0.2 and a (2-10 keV) luminosity of ∼ 4×10⁴⁶ erg s^-1 (in the quasar rest frame). The extended component is likely to be a candidate for a nearby galaxy group which accidentally coincides with the quasar.