2 X-RAY-CLUSTERS CLOSE TO LINE-OF-SIGHT OF THE LUMINOUS QSO HS-1700+6416

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 i s itself one of the most luminous QSOs known. Cluster A (1'40'' northw est of the QSO) is Abell 2246, while cluster B (3' northeast) is a hit herto unknown distant cluster. We have determined the redshifts of clu sters A and B as z = 0.25 and z = 0.34 respectively. Although both clu sters appear barely resolved by ROSAT, the X-ray surface brightness di stribution can be represented well by beta-models I(theta) = I-o(1 + ( theta/theta(c))(2))(-3 beta+0.5) where theta(c) is the cluster core ra dius (cf. Henry et al. 1993) if the detector point spread function is taken into account. Assuming beta = 2/3 we find core radii theta(c) (A ) = 14'' +/- 2'' and theta(c) (B) = 18'' +/- 2''. Gas temperatures are T (A) = 6 +/-3 . 10(7)K and T(B) = 3 +/- 1.5 . 10(7)K, X-ray luminosi ties are L-x(0.4 - 2keV rest frame) = 4.1 . 10(43) erg s(-1) and 8.45 . 10(43)erg s(-1) respectively (Ho = 50, q(o) = 1/2). Cluster B shows a giant luminous are located approximately 15'' (similar or equal to 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 exclu ded as reason for the high apparent luminosity of the QSO.