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Astron. Astrophys. 326, 489-492

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Research Note

Two X-ray clusters close to line of sight
of the luminous QSO HS 1700+6416*

D. Reimers1, F. Toussaint1, H.-J. Hagen1, H. Hippelein2, and K. Meisenheimer2

1Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
2Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany

Received 18 April 1996 / Accepted 27 March 1997


We report the serendipitous discovery with ROSAT of two X-ray clusters close to the line of sight of the QSO HS 1700+6416 (z = 2.72) which is itself one of the most luminous QSOs known. Cluster A (1'40'' northwest of the QSO) is Abell 2246, while cluster B (3' northeast) is a hitherto unknown distant cluster. We have determined the redshifts of clusters A and B as z = 0.25 and z = 0.44 respectively. Although both clusters appear barely resolved by ROSAT, the X-ray surface brightness distribution can be represented well by FORMULA -models FORMULA where FORMULA is the cluster core radius (cf. Henry et al. 1993) if the detector point spread function is taken into account. Assuming FORMULA we find core radii FORMULA (A) = 14" FORMULA 2" and FORMULA (B) = 18" FORMULA 2". Gas temperatures are T (A) = 6 FORMULA and FORMULA , X-ray luminosities are FORMULA rest frame) = 4.1 FORMULA and FORMULA respectively FORMULA .

Cluster B shows a giant luminous arc located approximately 15'' ( FORMULA 1 core radius) NW of the cluster center. We show that magnification of HS 1700+6416 by cluster lensing by the two X ray clusters can be excluded as reason for the high apparent luminosity of the QSO.

Key words: galaxies: clusters: individual: A 2246, HS 1700 B - quasars: individual: HS 1700+6416 - cosmology: gravitational lensing

*Based on observations by the ROSAT Observatory and the Calar Alto Observatory

Send offprint requests to: D. Reimers (dreimers@hs.uni-hamburg.de)

© European Southern Observatory (ESO) 1997

Online publication: September 18, 1997
Last change: October 15, 1997