MM-Newton Observations of two high redshift quasars: RX J1028-0844 and BR 0351-1034

Details MM-Newton Observations of two high redshift quasars: RX J1028-0844 and BR 0351-1034 MM-Newton Observations of two high redshift quasars: RX J1028-0844 and BR 0351-1034

2003-10-07

arxiv.org/abs/astro-ph/0310188v1

Astron.J.127:1,2004

Astronomy and Astrophysics

Astrophysics

14 pages, 5 figures; Accepted for publication in AJ, scheduled for January 2004

Scientific paper

10.1086/380615

We report the results of XMM-Newton observations of two high redshift quasars, one radio-loud, RX J1028.6-0844 (z=4.276) and one radio-quiet, BR 0351-1034 (z=4.351). We find that the evidence for strong excess absorption towards RX J1028-0844 is marginal at best, contrary to previous claims. The superior sensitivity and broader, softer energy range of XMM-Newton (0.2-10 keV) allows better determination of spectral parameters than much deeper ASCA observations (0.8-7 keV). Our XMM-Newton observations call into question several other ASCA results of strong absorption towards high redshift radio-loud quasars. RX J1028.6-0844 occupies the same parameter space in broad band spectral properties as the low redshift BL Lac objects, showing no obvious evolution with redshift. The radio-quiet quasar BR 0351-1024 became fainter between ROSAT and XMM observations by a factor of at least 5, but with the present data we cannot determine whether there is an associated spectral change. These observations do not support previous claims of weaker X-ray emission from high redshift radio-quiet quasars. The soft X-ray spectral slope required to reconstruct the ROSAT PSPC hardness ratio of BR 0351-1034 is about alpha-X=3.5, the steepest X-ray slope ever observed in a high redshift quasar, and similar to that of low redshift Narrow Line Seyfert 1 galaxies.

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