We report on Swift observations of four z > 2 radio-loud quasars ( 0212+735 , 0537–286 , 0836+710 , and 2149–307 ) , classified as blazars .
The sources , well-known emitters at soft-medium X-rays , were detected at > 5 \sigma with the BAT experiment in 15–150 keV .
No flux variability was detected within the XRT and BAT exposures , with the exception of 0836+710 which shows an increase of a factor 4 of the 15–150 keV flux on a timescale of one month .
The 0.3–10 keV spectra are well fitted by power law models , with rather hard continua ( photon indices \Gamma _ { XRT } \sim 1.3 - 1.5 ) ; similarly , the 15–150 keV spectra are described by power laws with \Gamma _ { BAT } \sim 1.3 - 1.8 .
The XRT data exhibit spectral curvature , which can be modeled either in terms of excess absorption along the line of sight , or a downward-curved broken power law .
In the former case , if the excess N _ { H } is at the rest-frame of the source , columns of N _ { H } ^ { z } = ( 0.3 - 6 ) \times 10 ^ { 22 } cm ^ { -2 } are measured .
Modeling of the SEDs of the four quasars shows that the emission at the higher frequencies , \buildrel > \over { \sim } 10 ^ { 16 } Hz , is dominated by the jet , while the steep optical-to-UV continua , observed with the UVOT , can be attributed to thermal emission from the accretion disk .
The disk luminosity is between 1 % and 10 % the jet power , similar to other powerful blazars .