分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We study the ensemble X-ray variability properties of Active Galactic Nuclei (AGN) over a large range of timescales (20 ks $\leq T\leq$ 14 yrs), redshift ($0\leq z \lesssim 3$), luminosities ($10^{40}$ erg s$^{-1}\leq L_X\leq 10^{46}$ erg s$^{-1}$) and black hole (BH) masses ($10^6 \leq $M$_\odot \leq 10^9$). We propose the use of the variance-frequency diagram, as a viable alternative to the study of the power spectral density (PSD), which is not yet accessible for distant, faint and/or sparsely sampled AGN. We show that the data collected from archival observations and previous literature studies are fully consistent with a universal PSD form which does not show any evidence for systematic evolution of shape or amplitude with redshift or luminosity, even if there may be differences between individual AGN at a given redshift or luminosity. We find new evidence that the PSD bend frequency depends on BH mass and, possibly, on accretion rate. We finally discuss the implications for current and future AGN population and cosmological studies.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present the X-ray imaging and spectral analysis of the diffuse emission around the Spiderweb galaxy at z=2.16 and of its nuclear emission, based on a deep (700 ks) Chandra observation. We characterize the nuclear emission and computed the contamination in the surrounding regions due to the wings of the instrument PSF. Then, we quantified the extended emission within 12". We find that the Spiderweb galaxy hosts a mildly absorbed quasar, with modest yet significant variability on a timescale of ~1 year. We find that the emission in the jet regions is well described by a power law with Gamma~2-2.5, and it is consistent with IC upscattering of the CMB photons by the relativistic electrons. We also find a roughly symmetric, diffuse emission within a radius of ~100 kpc. This emission is consistent with thermal bremsstrahlung from a hot ICM with a temperature of kT=2.0_{-0.4}^{+0.7} keV, and a metallicity of Z<1.6Z_sun. The average electron density within 100 kpc is n_e=(1.51+-0.24+-0.14)E-2 cm^{-3}, corresponding to an upper limit for the total ICM mass of <=(1.76+-0.30+-0.17)E+12 M_sun (where error bars are 1 sigma statistical and systematic, respectively). If we apply hydrostatic equilibrium to the ICM, we measure a total gravitational mass M(<100 kpc)=(1.5^{+0.5}_{-0.3})E+13 M_sun and, extrapolating at larger radii, we estimate a total mass M_{500}=(3.2^{+1.1}_{-0.6})E+13 M_sun within a radius of r_{500}=(220+-30) kpc. We conclude that the Spiderweb protocluster shows significant diffuse emission within a radius of 12 arcsec, whose major contribution is provided by IC scattering associated with the radio jets. Outside the jet regions, we also identified thermal emission within a radius of ~100 kpc, revealing the presence of hot, diffuse baryons that may represent the embryonic virialized halo of the forming cluster.