The extreme X-ray luminosity of the z = 4.72 radio-loud quasar GB 1428+4217

A. C. Fabian, W. N. Brandt, R. G. McMahon, I. M. Hook

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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 languageEnglish (US)
Pages (from-to)L5-L7
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1997

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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