A catalogue of optical to X-ray spectral energy distributions of z ≈ 2 quasars observed with Swift – I. First results

Abstract

We present the Swift optical to X-ray spectral energy distributions (SEDs) of 44 quasars at redshifts z approximate to 2 observed by Swift, part of a larger program to establish and characterize the optical through X-ray SEDs of moderate-redshift quasars. Here, we outline our analysis approach and present preliminary analysis and results for the first third of the full quasar sample. Not all quasars in the sample are detected in X-rays; all of the X-ray-detected objects so far are radio loud. As expected for radio-loud objects, they are X-ray bright relative to radioquiet quasars of comparable optical luminosities, with an average alpha(ox) = 1.39 +/- 0.03 (where alpha(ox) is the power-law slope connecting the monochromatic flux at 2500 angstrom and at 2 keV), and display hard X-ray spectra. We find integrated 3000 angstrom-25 keV accretion luminosities of between 0.7 x 10(46) erg s (1) and 5.2 x 10(47) erg s (1). Based on single-epoch spectroscopic virial black hole mass estimates, we find that these quasars are accreting at substantial Eddington fractions, 0.1 less than or similar to L/L-Edd less than or similar to 1.