X-ray properties of high-redshift Radio Loud and Radio Quiet Quasars observed by Chandra

F. Shaban; A. Siemiginowska; R. M. Suleiman; M. El-Nawawy; A. Ali

doi:10.1016/j.jheap.2022.10.002

paper

X-ray properties of high-redshift Radio Loud and Radio Quiet Quasars observed by Chandra

arXiv:2301.02866 · doi:10.1016/j.jheap.2022.10.002

Abstract

We performed a study of high redshift ( $z > 2$ ) quasars, looking for the main differences between Radio Loud Quasars (RLQ) and Radio Quiet Quasars (RQQ) in the X-ray band. Our sample of 472 RQQ and 81 RLQ was selected by cross-matching the SDSS DR7 quasars catalog with the Chandra Source Catalog. We computed the X-ray luminosity for the two samples and confirmed the X-ray luminosity excess of RLQ over RQQ. We fit the X-ray spectra assuming the absorbed power law model and obtained the photon index ( $Γ$ ) values for all the sources in the sample. We excluded quasars with a low number of counts ( $< 10$ ) and large uncertainty on the best-fit photon index ( $Γ_{er r} > 1$ ), and obtained the mean values of $Γ_{R L Q} = 1.70_{- 0.33}^{+ 0.36}$ and $Γ_{R QQ} = 2.19_{- 0.44}^{+ 0.46}$ for the RLQ and RQQ samples, respectively, showing that the RLQ have flatter (harder) X-ray spectra than RQQ. The Kuiper-two test confirms this result with the significant difference between the RLQ and RQQ photon index distributions ( $D_{k} = 0.37$ and P-value $= 1 0^{- 6}$ ). We also evaluated the hardness ratio distributions and confirmed that the spectra of RLQ are flatter than the spectra of the RQQ. The RLQ's hard-to-soft ratio distribution is skewed towards the hard X-ray band, while the RQQ is towards the soft X-ray band. The hard-to-medium and medium-to-soft ratios show no difference.

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