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Astron. Astrophys. 326, 489-492 (1997)

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Research Note

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

D. Reimers 1, F. Toussaint 1, H.-J. Hagen 1, H. Hippelein 2 and K. Meisenheimer 2

1 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
2 Max-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)

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© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997