We report on a ROSAT High Resolution Imager observation of the radio-loud quasar GB 1428+4217, which is at a redshift z = 4.72. The quasar was well detected, with a flux in the observed 0.1-2.4 keV band of ∼10 -12 erg cm -2 s -1. Our result confirms that the object in the catalogue of serendipitous X-ray sources, WGACAT, is indeed the quasar. GB 1428+4217 is therefore the brightest X-ray source above a redshift of 4 and has an extremely high isotropic X-ray luminosity, which exceeds that in other (observed) bands. The observed spectral energy distribution of the object therefore peaks at X-ray, or even shorter, wavelengths. We speculate that the emission in the object is beamed toward us.
|Original language||English (US)|
|Journal||Monthly Notices of the Royal Astronomical Society|
|State||Published - Dec 1 1997|
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science