SIMBAD references

A series of ROSAT PSPC observations of 3C 273 performed between June 1990 and December 1991 to investigate the spectral behaviour of the quasar have, as a byproduct, resulted in the detection of 16 additional X-ray sources within a 20 arcmin radius around the target. Only one of these sources had been found before by the Einstein observatory. 10 of the 17 PSPC sources were also detected in one HRI observation. We list optical counterparts for 10 of the X-ray sources and discuss their probable nature. Our aim was to see whether sources exist close to 3C 273 which could have contaminated previous observations of this source by non-imaging X-ray instruments. Of particular interest is an object which was detected as a variable high energy X-ray source by SIGMA, 15 arcmin away from 3C 273 for which we discuss the low energy X-ray counterpart. We conclude that most likely no significant contamination has taken place in earlier high energy X-ray observations of 3C 273.