The luminous quasar HS 1700+6416 and the shape of the "big bump" below 500 A.

Abstract

In the course of the Hamburg quasar survey a bright (V = 16.1) high redshift (z = 2.72) quasar has been discovered. Follow-up optical high (0.4 A) and low (6 A) resolution spectrophotometry together with IUE observations are presented. With a luminosity at λ_rest_ = 1450 A, L_1450_ = 6 x 10^32^ erg s^-1^ Hz^-1^, HS1700+6416 is the second most luminous quasar known. More important, it is the first one to be detected down to a rest wavelength of 330 A. Although intervening Lyman line and continuum absorption severely depress the observed spectrum between λ_rest_ ~ 850 A and 450 A, the intrinsic quasar flux distribution per unit wavelength, Fλ, unexpectedly continues to rise sharply toward shorter wavelengths up to at least λ_rest_ = 330 A. If this result is applicable to quasars and AGN's as a class, it implies that the turn-over of the so-called "big bump" in these objects lies beyond ~ 3 Rydbergs. Besides the usual "Lyman α forest", one strong absorption system at z = 2.43 is particularly noteworthy which shows the presence of the H Lyα, Lyβ and CIV1550 lines as well as a Lyman continuum edge. A large scale Lyα absorbing structure is seen with IUE which extends over the redshift range 0.08-0.21. It is most likely associated with two galaxies whose angular separation from the QSO, θ, and redshifts are respectively θ = 11", z = 0.086 and θ = 18", z = 0.19. There is no evidence of gravitational lensing at a seeing of 0.9".