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Astron. Astrophys. 346, L5-L8 (1999)

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Letter to the Editor

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

Joachim Wambsganss 1, Hermann Brunner 1, Sabine Schindler 2 and Emilio Falco 3

1 Astrophysikalisches Institut Potsdam, Sternwarte 16, D-14482 Potsdam, Germany (jwambsganss, hbrunner@aip.de)
2 Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead L41 1LD, UK (sas@astro.livjm.ac.uk)
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA (falco@cfa.harvard.edu)

Received 2 March 1999 / Accepted 20 April 1999


We report the first detection of the gravitationally lensed quasar Q2237+0305 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 images. This corresponds to an X-ray flux of [FORMULA] erg/cm2/sec and an X-ray luminosity of [FORMULA] 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 about 330 source photons. The signal is consistent with no variability, but with low significance. This detection is promising in view of the upcoming X-ray missions with higher spatial/spectral resolution and/or collecting power (Chandra X-ray Observatory, XMM and ASTRO-E).

Key words: cosmology: observations – cosmology: gravitational lensing – galaxies: quasars: individual: Q2237+0305 – X-rays: galaxies – X-rays: general

© European Southern Observatory (ESO) 1999

Online publication: May 6, 1999