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Register a new userXMM-Newton observations of the extremely X-ray luminous quasar CFHQS J142952+544717=SRGE J142952.1+544716 at redshift z=6.18
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We present results from a 20 ks XMM-Newton DDT observation of the radio-load quasar CFHQS J142952+544717 at z=6.18, whose extreme X-ray luminosity was recently revealed by the SRG/eROSITA telescope in the course of its first all-sky survey. The quasar has been confidently detected with a total of $sim 1400$ net counts in the 0.2-10 keV energy band (1.4 to 72 keV in the objects rest frame). Its measured spectrum is unusually soft and can be described by an absorbed power-law model with a photon index of $Gamma = 2.5pm0.2$. There are no signs of a high-energy cutoff or reflected component, with an 90 % upper limit on the fluorescence iron K$alpha$ equivalent width of $approx 290$ eV and the corresponding upper limit on the iron K-edge absorption depth of 0.6. We have detected, at the $> 95%$ confidence level, an excess absorption above the Galactic value, corresponding to a column density $N_H= 3pm2 times 10^{22}$ cm$^{-2}$ of material located at z=6.18. The intrinsic luminosity of CFHQS J142952+544717 in the 1.4 to 72 keV energy band is found to be $5.5_{-0.6}^{+0.8} times 10^{46}$ erg s$^{-1}$. We did not detect statistically significant flux changes between two SRG scans and the XMM-Newton observation, spanning over $sim 7.5$ months, implying that the quasar remained at this extremely high luminosity level for at least a month in its rest frame. We put forward the hypothesis that the extreme X-ray properties of CFHQS J142952+544717 are associated with inverse Compton scattering of cosmic microwave background photons (at z=6.18) in its relativistic jets.
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SRGE J170245.3+130104 was discovered by the eROSITA telescope aboard the SRG space observatory on March 13-15, 2020 during the first half-year scan of its all-sky X-ray survey. The optical counterpart of the X-ray source was photometrically identified as a distant quasar candidate at $zapprox5.5$. Follow-up spectroscopic observations, done in August/September 2020 with the SCORPIO-II instrument at the BTA 6-m telescope, confirmed that SRGE J170245.3+130104 is a distant quasar at redshift z=5.466. The X-ray luminosity of the quasar during the first half-year scan of the eROSITA all-sky survey was $3.6^{+2.1}_{-1.5}times 10^{46}$ erg/s (in the 2-10 keV energy range), whereas its X-ray spectrum could be described by a power law with a slope of $Gamma=1.8^{+0.9}_{-0.8}$. Six months later (September 13-14, 2020), during the second half-year scan of the eROSITA all-sky survey, the quasar was detected again and its X-ray luminosity had decreased by a factor of 2 (at the $approx 1.9sigma$ confidence level). The SRGE J170245.3+130104 proves to be the most X-ray luminous among all known X-ray quasars at $z>5$. It is also one of the radio-loudest distant quasars (with radio-loudness $Rsim10^3$), which may imply that it is a blazar. In the Appendix, we present the list of all $z>5$ quasars detected in X-rays to date.
We present new X-ray observations of luminous heavily dust-reddened quasars (HRQs) selected from infrared sky surveys. HRQs appear to be a dominant population at high redshifts and the highest luminosities, and may be associated with a transitional blowout phase of black hole and galaxy co-evolution models. Despite this, their high-energy properties have been poorly known. We use the overall sample of $10$ objects with XMM-Newton coverage to study the high-energy properties of HRQs at $left< L_{rm bol} right> = 10^{47.5}$ erg/s and $left< z right>= 2.5$. For the seven sources with strong X-ray detections, we perform spectral analyses. These find a median X-ray luminosity of $left< L_{rm 2-10,keV} right> = 10^{45.1}$ erg/s, comparable to the most powerful X-ray quasars known. The gas column densities are $N_{rm H}=(1$-$8)times 10^{22}$ cm$^{-2}$, in agreement with the amount of dust extinction observed. The dust to gas ratios are sub-Galactic, but are higher than found in local AGN. The intrinsic X-ray luminosities of HRQs are weak compared to the mid-infrared ($L_{rm 6mu m}$) and bolometric luminosities ($L_{rm bol}$), in agreement with findings for other luminous quasar samples. For instance, the X-ray to bolometric corrections range from $kappa_{rm bol}approx 50$-$3000$. The moderate absorption levels and accretion rates close to the Eddington limit ($left< lambda_{rm Edd} right>=1.06$) are in agreement with a quasar blowout phase. Indeed, we find that the HRQs lie in the forbidden region of the $N_{rm H}$-$lambda_{rm Edd}$ plane, and therefore that radiation pressure feedback on the dusty interstellar medium may be driving a phase of blowout that has been ongoing for a few $10^{5}$ years. The wider properties, including [OIII] narrow-line region kinematics, broadly agree with this interpretation.
We report the discovery of X-ray emission from CFHQS J142952+544717, the most distant known radio-loud quasar at z=6.18, on Dec. 10--11, 2019 with the eROSITA telescope on board the SRG satellite during its ongoing all-sky survey. The object was identified by cross-matching an intermediate SRG/eROSITA source catalog with the Pan-STARRS1 distant quasar sample at 5.6 < z < 6.7. The measured flux $sim 8 times 10^{-14}$ erg cm$^{-2}$ s$^{-1}$ in the 0.3--2 keV energy band corresponds to an X-ray luminosity of $2.6^{+1.7}_{-1.0}times 10^{46}$ erg s$^{-1}$ in the 2--10 keV rest-frame energy band, which renders CFHQS J142952+544717 the most X-ray luminous quasar ever observed at z > 6. Combining our X-ray measurements with archival and new photometric measurements in other wavebands (radio to optical), we estimate the bolometric luminosity of this quasar at $sim (2$--$3) times 10^{47}$ erg s$^{-1}$. Assuming Eddington limited accretion and isotropic emission, we infer a lower limit on the mass of the supermassive black hole of $sim 2times 10^9 M_odot$. The most salient feature of CFHQS J142952+544717 is its X-ray brightness relative to the optical/UV emission. We argue that it may be linked to its radio-loudness (although the object is not a blazar according to its radio properties), specifically to a contribution of inverse Compton scattering of cosmic microwave background photons off relativistic electrons in the jets. If so, CFHQS J142952+544717 might be the tip of the iceberg of high-z quasars with enhanced X-ray emission, and SRG/eROSITA may find many more such objects during its 4 year all-sky survey.
We present the results of optical spectroscopy for 19 quasar candidates at photometric redshifts $zphot gtrsim 3$, Nobs of which enter into the Khorunzhev et al.~(2016) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the textit{3XMM-DR4}catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for a quasi-random sample of new candidates at the 1.6-m Azt telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. The spectra at Azt were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. Fourteen of the Nobs candidates actually have turned out to be quasars; 10 of them are at spectroscopic redshifts z > 3. The high purity of the sample of new candidates suggests that the purity of the entire K16 catalog of quasars is probably 70--80%. One of the most distant ($zspec=5.08$) optically bright ($i^primelesssim 21$) quasars ever detected in X-ray surveys has been discovered.
Observations of relaxed, massive and distant clusters can provide important tests of standard cosmological models e.g. using the gas mass fraction. We study the very luminous, high redshift ($z=0.902$) galaxy cluster ClJ120958.9+495352 using XMM-Newton data and measure the temperature profile and cooling time to investigate the dynamical status with respect to the presence of a cool core as well as global cluster properties. We use HST weak lensing data to estimate its total mass and determine the gas mass fraction. We perform a spectral analysis using an XMM-Newton observation of 15ks cleaned exposure time. As the treatment of the background is crucial, we use two different approaches to account for the background emission to verify our results. We account for point-spread-function effects and deproject our results to estimate the gas mass fraction of the cluster. We measure weak lensing galaxy shapes from mosaic HST imaging and select background galaxies photometrically in combination with imaging data from the William Herschel Telescope. The X-ray luminosity of ClJ120958.9+495352 in the 0.1-2.4keV band estimated from our XMM-Newton data is $L_X = (13.4_{-1.0}^{+1.2})times10^{44}$erg/s and thus it is one of the most X-ray luminous clusters known at similarly high redshift. We find clear indications for the presence of a cool core from the temperature profile and the central cooling time, which is very rare at such high redshifts. Based on the weak lensing analysis we estimate a cluster mass of $M_mathrm{500}/10^{14}M_odot=4.4^{+2.2}_{-2.0}(mathrm{stat.})pm0.6(mathrm{sys.})$ and a gas mass fraction of $f_mathrm{gas,2500} = 0.11_{-0.03}^{+0.06}$ in good agreement with previous findings for high redshift and local clusters.
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