We report exploratory Chandra observations of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.30. The quasar is clearly detected by Chandra with a possible component of extended emission. The rest-frame 2-10 keV luminosity is 9.0(+4.5)(+9.1) x 10(45) erg s(-1) with an inferred photon index of G = 3.03(-0.70)(+0.78). This quasar is X-ray bright, with an inferred X-ray-to-optical flux ratio alpha(ox) = -1.22(-0.05)(+0.07), higher than the values found in other quasars of comparable ultraviolet luminosity. The properties inferred from this exploratory observation indicate that this ultraluminous quasar might be growing with super-Eddington accretion and probably viewed with a small inclination angle. Deep X-ray observations will help to probe the plausible extended emission and better constrain the spectral features for this ultraluminous quasar.

A brief Chandra observation of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.326 showed it to be a relatively bright, soft X-ray source with a count rate of about 1 count ks(-1). In this article, we present results for the quasar from a 65-ks XMM-Newton observation, which constrains its spectral shape well. The quasar is clearly detected with a total of similar to 460 net counts in the 0.2-10 keV band. The spectrum is characterized by a simple power-law model with a photon index of Gamma = 2.30(-0.10)(+0.10) and the intrinsic 2-10 keV luminosity is 3.14 x 10(45) erg s(-1). The 1 sigma upper limit to any intrinsic absorption column density is N-H = 6.07 x 10(22) cm(-2). No significant iron emission lines were detected. We derive an X-ray-to- optical flux ratio alpha(ox) of -1.74 +/- 0.01, consistent with the values found in other quasars of comparable ultraviolet luminosity. We did not detect significant flux variations either in the XMM-Newton exposure or between XMM-Newton and Chandra observations, which are separated by similar to 8 months. The X-ray observation enables the bolometric luminosity to be calculated after modelling the spectral energy distribution: the accretion rate is found to be sub-Eddington.

We report new IRAM/PdBI, JCMT/SCUBA-2, and VLA observations of the ultraluminous quasar SDSS J010013.02+280225.8 (hereafter, J0100+2802) at z =. 6.3, which hosts the most massive supermassive black hole (SMBH), 1.24 x 10(10) M circle dot, that is known at z > 6. We detect the [C II] 158 mu m fine structure line and molecular CO(6-5) line and continuum emission at 353, 260, and 3 GHz from this quasar. The CO(2-1) line and the underlying continuum at 32 GHz are also marginally detected. The [C II] and CO detections suggest active star formation and highly excited molecular gas in the quasar host galaxy. The redshift determined with the [C II] and CO lines shows a velocity offset of similar to 1000 km s(-1) from that measured with the quasar Mg II line. The CO (2-1) line luminosity provides a direct constraint on the molecular gas mass, which is about (1.0 +/- 0.3) x 10(10) M circle dot We estimate the FIR luminosity to be (3.5 +/- 0.7) x 10(12) L circle dot, and the UV-to-FIR spectral energy distribution of J0100 +2802 is consistent with the templates of the local optically luminous quasars. The derived [C II]-to-FIR luminosity ratio of J0100+2802 is 0.0010 +/- 0.0002, which is slightly higher than the values of the most FIR luminous quasars at z similar to 6. We investigate the constraint on the host galaxy dynamical mass of J0100 vertical bar 2802 based on the [C II] line spectrum. It is likely that this ultraluminous quasar lies above the local SMBH-galaxy mass relationship, unless we are viewing the system at a small inclination angle.

We report Very Long Baseline Array (VLBA) observations of the 1.5 GHz radio continuum emission of the z = 6.326 quasar SDSS J010013.02+ 280225.8 (hereafter J0100+ 2802). J0100+ 2802 is by far the most optically luminous and is a radio-quiet quasar with the most massive black hole known at z > 6. The VLBA observations have a synthesized beam size of 12.10 mas x5.36 mas (FWHM), and detected the radio continuum emission from this object with a peak surface brightness of 64.6 +/- 9.0 mu Jy beam(-1) and a total flux density of 88 +/- 19 mu Jy. The position of the radio peak is consistent with that from SDSS in the optical and Chandra in the X-ray. The radio source is marginally resolved by the VLBA observations. A 2D Gaussian fit to the image constrains the source size to (7.1 +/- 3.5) mas x (3.1 +/- 1.7) mas. This corresponds to a physical scale of (40 +/- 20) pc x (18 +/- 10) pc. We estimate the intrinsic brightness temperature of the VLBA source to be T-B = (1.6 +/- 1.2) x 10(7) K. This is significantly higher than the maximum value in normal star-forming galaxies, indicating an active galactic nucleus (AGN) origin for the radio continuum emission. However, it is also significantly lower than the brightness temperatures found in highest-redshift radio-loud quasars. J0100+ 2802 provides a unique example for studying the radio activity in optically luminous and radio-quiet AGNs in the early universe. Further observations at multiple radio frequencies will accurately measure the spectral index and address the dominant radiation mechanism of the radio emission.