1,721,414 research outputs found
Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback
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The habitability of the Milky Way during the active phase of its central supermassive black hole
Full text linkAbstractDuring the peak of their accretion phase, supermassive black holes in galactic cores are known to emit very high levels of ionizing radiation, becoming visible over intergalactic distances as quasars or active galactic nuclei (AGN). Here, we quantify the extent to which the activity of the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*), may have affected the habitability of Earth-like planets in our Galaxy. We focus on the amount of atmospheric loss and on the possible biological damage suffered by planets exposed to X-ray and extreme ultraviolet (XUV) radiation produced during the peak of the active phase of Sgr A*. We find that terrestrial planets could lose a total atmospheric mass comparable to that of present day Earth even at large distances (~1 kiloparsec) from the galactic center. Furthermore, we find that the direct biological damage caused by Sgr A* to surface life on planets not properly screened by an atmosphere was probably significant during the AGN phase, possibly hindering the development of complex life within a few kiloparsecs from the galactic center.</jats:p
spectrum of the radio-loud quasar 3C 215: Slim accretion disk or SMBH binary
No full textContext. Radio-loud active galactic nuclei (RL AGN) exhibit very powerful jet emission in the radio band, while the radio-quiet (RQ) AGN do not. This RL-RQ dichotomy would imply a sharp difference existing among these two classes, however, modern theoretical models and observations suggest a common nuclear environment that is possibly characterized by different working regimes.
Aims. We explore the geometrical structure and mutual interactions of the innermost components of the broad line radio galaxy 3C 215, with a particular focus on the accretion and ejection mechanisms involving the central supermassive black hole (SMBH). We compare these observational features with those of the RQ Seyfert 1 galaxies. Investigating their differences is aimed at improving our understanding of the jet launching mechanisms and devising an explanation for why this phenomenon is efficient only in a small fraction of all the AGNs.
Methods. Using high-quality data from a ∼60 ks observation with XMM-Newton, we carried out a detailed X-ray spectral analysis of 3C 215 in the broad energy range of 0.5−10 keV. We modeled the spectrum with an absorbed double power-law model for the primary continuum, reprocessed by reflection from ionized and cold neutral material and modified by relativistic blurring. We also compared our results with those of earlier multi-wavelength observations.
Results. We obtained a primary continuum photon index from the corona, namely, Γ1 = 1.97 ± 0.06, along with evidence of a jet contribution, modeled as a power law with photon index of Γ2 ≃ 1.29. The reflector, which is possibly attributed to the accretion disk and portions of the broad-line region (BLR), is ionized ( erg s−1 cm) and relatively distant from the SMBH (Rin > 38 Rg), where Rg = GMBH/c2 is the gravitational radius. The obscuring torus seems patchy, dust-poor, and inefficient, while the jet emission shows a twisted and knotted geometry. We propose three scenarios to describe the following characteristics: 1. An ADAF state in the inner disk; 2. A slim accretion disk; and 3. A sub-pc SMBH binary system (SMBHB).
Conclusions. While the first scenario is not in agreement with the SMBH accretion regime, the slim disk scenario is consistent with the observational features of this radio galaxy, showing that 3C 215 is similar to non-jetted AGNs, accreting at a high rate. Nonetheless, the first two scenarios are unable to account for the particular shape of 3C 215 jet emission. The SMBHB scenario seems to be in agreement with almost all 3C 215 observational features, but we are not able to unequivocally determine this source as a strong SMBHB candidate. A final determination will require further analysis
Evidence for Ultra-Fast Outflows in Radio-Quiet AGNs: III - Location and Energetics
Full text linkUsing the results of a previous X-ray photo-ionization modelling of blue-shifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs observed with XMM-Newton, in this letter we estimate the location and energetics of the associated ultrafast outflows (UFOs). Due to significant uncertainties, we are essentially able to place only lower/upper limits. On average, their location is in the interval approx.0.0003-0.03pc (approx.10(exp 2)-10(exp 4)tau(sub s) from the central black hole, consistent with what is expected for accretion disk winds/outflows. The mass outflow rates are constrained between approx.0.01- 1 Stellar Mass/y, corresponding to approx. or >5-10% of the accretion rates. The average lower-upper limits on the mechanical power are logE(sub K) approx. or = 42.6-44.6 erg/s. However, the minimum possible value of the ratio between the mechanical power and bolometric luminosity is constrained to be comparable or higher than the minimum required by simulations of feedback induced by winds/outflows. Therefore, this work demonstrates that UFOs are indeed capable to provide a significant contribution to the AGN r.osmological feedback, in agreement with theoretical expectations and the recent observation of interactions between AGN outflows and the interstellar medium in several Seyferts galaxies
The X-ray/UV ratio in Active Galactic Nuclei: dispersion and variability
Full text linkThe relation between the index and the optical/UV luminosity
(), a by product of the X-ray - optical/UV luminosity relation, is
affected by a relatively large dispersion, due to variability in the
within single sources (intra-source dispersion) and variations of
fundamental physical parameters from source to source (inter-source
dispersion). We use archival data from the XMMSSC and from the XMMOM-SUSS3. We
select a sub-sample in order to decrease the dispersion of the relation due to
the presence of Radio-Loud and Broad Absorption Line objects, and to
absorptions in both X-ray and optical/UV bands. We analyse the dependence of
the residuals of the relation on various physical parameters in order to
characterise the inter-source dispersion. We find a total dispersion of ~0.12
and, using the Structure Function, we find that intrinsic variability
contributes for 56% of the variance of the relation. We find weak but
significant dependences of the residuals of the relation on black-hole (BH)
mass and on Eddington ratio, confirmed by a multivariate regression analysis of
as a function of optical/UV luminosity and the above quantities.
We find a weak positive correlation of both the and the residuals
of the relation with inclination indicators (FWHM(H) and EW[O])
suggesting a weak increase of X-ray/UV ratio with the viewing angle. Our
results suggest the possibility of selecting a sample of objects, based on
their viewing angle and/or BH mass and Eddington ratio, for which the
relation is as tight as possible, in light of the use of
the X-ray - optical/UV luminosity relation to build a distance modulus (DM) -
plane and estimate cosmological parameters
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