Volume 563, March 2014
|Number of page(s)||5|
|Published online||05 March 2014|
X-ray observation of ULAS J1120+0641, the most distant quasar at z = 7.08
INAF, Osservatorio Astronomico di Brera, via Brera 28,
2 INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3 INAF, via E. Bassini 15, 20133 Milano, Italy
4 Dipartimento di Astronomia, Università degli Studi di Bologna, via Ranzani 1, 40127 Bologna, Italy
Received: 14 November 2013
Accepted: 31 January 2014
We probe the emission mechanism of the accreting super massive black holes in the high redshift Universe and, to do this, we study the X-ray spectrum of ULAS1120+064, the highest redshift quasar detected so far at z = 7.085, which has been deeply observed (340 ks) by XMM-Newton. Despite the long integration time, the spectral analysis is limited by the poor statistics, with only 150 source counts being detected. We measured the spectrum in the 2−80 keV rest-frame (0.3−10 keV observed) energy band. Assuming a simple power law model, we find a photon index of 2.0 ± 0.3 and a luminosity of 6.7 ± 0.3 × 1044 erg s-1 in the 2−10 keV band, while the intrinsic absorbing column can only be loosely constrained (NH < 1023 cm-2). Combining our measure with published data, we calculate that the X-ray-to-optical spectral index αOX is 1.8 ± 0.1, in agreement with the αOX-UV luminosity correlation that is valid for lower redshift quasars. This is the second time that a z > 6 quasar has been investigated through a deep X-ray observation. In agreement with previous studies of z ~ 6 AGN samples, we do not find any hint of evolution in the broadband energy distribution. Indeed from our dataset, ULAS 1120+0641 is indistinguishable from the population of optically bright quasar at lower redshift.
Key words: quasars: supermassive black holes / quasars: individual: ULAS J1120+0641 / early Universe
© ESO, 2014
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