Three in One: The VLBI Radio View of the X-ray Quasar RX J1456.0+5048
  RX J1456.0+5048 is a prominent X-ray source detected by ROSAT. There is
~100-mJy level radio emission associated with the X-ray source. However,
interferometric observations with increasing angular resolution revealed that
three distinct objects located within 2 arcmin are responsible for the measured
total flux density. Whether these radio sources lining up in the sky are
physically associated or just seen close to each other in projection is not
immediately clear. In fact, incorrect cross-identification of the X-ray,
optical and radio sources can already be found in the literature. Here we
summarise the current knowledge about this intriguing group of objects, where
two of the three sources show compact radio emission detected with very long
baseline interferometry (VLBI). We present a VLBI image of one of them for the
first time, based on archival European VLBI Network (EVN) data taken at 5 GHz.
