Deep XMM-Newton Observations of an X-ray Weak Broad Absorption Line Quasar at z=6.5

We report X-ray observations of the most distant known gravitationally lensed quasar, J0439+1634 at z = 6.52, which is also a broad absorption line (BAL) quasar, using the XMM-Newton Observatory. With a 130 ks exposure, the quasar is significantly detected as a point source at the optical position with a total of 358(-19)(+19) net counts using the EPIC instrument. By fitting a power law plus Galactic absorption model to the observed spectra, we obtain a spectral slope of Gamma = 1.45(-0.09)(+0.10). The derived optical-to-X-ray spectral slope alpha(ox) is -2.07(+0.01)(-0.01), suggesting that the X-ray emission of J0439+ 1634 is weaker by a factor of 18 than the expectation based on its 2500 angstrom luminosity and the average aox versus luminosity relationship. This is the first time that an X-ray weak BAL quasar at z > 6 has been observed spectroscopically. Its X-ray weakness is consistent with the properties of BAL quasars at lower redshift. By fitting a model including an intrinsic absorption component, we obtain intrinsic column densities of N-H = 2.8(-0.6)(0.7) x 10(23) cm(-2) and N-H = 4.3(-1.5)(+1.8) x 10(23) cm(-2), assuming a fixed G of 1.9 and a free Gamma, respectively. The intrinsic rest-frame 2-10 keV luminosity is derived as (9.4-15.1) x 10(43) erg s(-1), after correcting for lensing magnification (mu = 51.3). The absorbed power-law model fitting indicates that J0439+1634 is the highest redshift obscured quasar with a direct measurement of the absorbing column density. The intrinsic high column density absorption can reduce the X-ray luminosity by a factor of 3-7, which also indicates that this quasar could be a candidate intrinsically X-ray weak quasar.