The gravitationally lensed quasar Q2237+0305 in X-rays: ROSAT HRI detection of the "Einstein Cross"

We report the first detection of the gravitationally lensed quasar Q2237+03 05 in X-rays. With a ROSAT/HRI exposure of 53 ksec taken in Nov./Dec. 1997, we found a count rate of 0.006 counts per second for the combined four ima ges. This corresponds to an X-ray flux of 2.2 x 10(-13) erg/cm(2)/sec and a n X-ray luminosity of 4.2 x 10(45) erg/sec (in the ROSAT energy window 0.1- 2.4 keV). The ROSAT/HRI detector is not able to resolve spatially the four quasar images (maximum separation 1.8 arcsec). The analysis is based on abo ut 330 source photons. The signal is consistent with no variability, but wi th low significance. This detection is promising in view of the upcoming X- ray missions with higher spatial/spectral resolution and/or collecting powe r (Chandra X-ray Observatory, XMM and ASTRO-E).