1,721,213 research outputs found
Does the X-ray emission of the luminous quasar RBS 1124 originate in a mildly relativistic outflowing corona?
No full textWe have observed the luminous (L2−10 keV ≃ 6 × 1044 erg s−1) radio-quiet quasar RBS 1124 (z = 0.208) with Suzaku. We report the detection of a moderately broad iron (Fe) line and of a weak soft X-ray excess. The X-ray data are very well described by a simple model comprising a power-law X-ray continuum plus its reflection off the accretion disc. If the inner disc radius we measure (rin ≤ 3.8 gravitational radii) is identified with the innermost stable circular orbit of the black hole space–time, we infer that the black hole powering RBS 1124 is rotating rapidly with spin a ≥ 0.6. The soft excess contribution in the 0.5–2 keV band is ∼15 per cent, about half than that typically observed in unobscured Seyfert 1 galaxies and quasars, in line with the low disc reflection fraction we measure (Rdisc ≃ 0.4). The low reflection fraction cannot be driven by disc truncation which is at odds not only with the small inner disc radius we infer but, most importantly, with the radiatively efficient nature of the source (LBol/LEdd ≃ 1). A plausible explanation is that the X-ray corona is the base of a failed jet (RBS 1124 being radio-quiet) and actually outflowing at mildly relativistic speeds. Aberration reduces the irradiation of the disc, thus forcing a lower than standard reflection fraction, and halves the inferred source intrinsic luminosity, reducing the derived Eddington ratio from ≃1 to ≃0.5. A partial covering model provides a statistically equivalent description of the 0.3–10 keV data, but provides a worse fit above 10 keV. More importantly, its properties are not consistent with being associated to the Fe emission line, worsening the degree of self-consistency of the model. Moreover, the partial covering model implies that RBS 1124 is radiating well above its Eddington luminosity, which seems unlikely and very far off from previous estimates
XMM-Newton first X-ray detection of the low-ionization broad absorption line quasar PG 1700+518
No full textWe report the first high-energy detection of PG 1700+518, a well-known low-ionization broad absorption line quasar (quasi-stellar object, QSO). Due to previous X-ray non-detection, it was classified as soft X-ray weak QSO. We observed PG 1700+518 with XMM-Newton for about 60 ks divided in three exposures. The spectrum below 2 keV is very steep, Γ ̃ 2.4-3.8, while at higher energies the extremely flat emission (photon index Γ ̃ 0.15, when modelled with a power law) suggests the presence of strong absorption (NH, pl ̃ 2 × 10^23 cm-2, Γ fixed to 1.8) or a reflection-dominated continuum. The broad-band flux is consistent with previous non-detection. Simultaneous European Photon Imaging Camera (EPIC) and Optical Monitor (OM) data confirm its X-ray weakness (observedαox ̃-2.2). The level of obscuration derived from the X-ray spectra of PG 1700+518 cannot explain its soft X-ray nuclear weakness unless a column density of NH≳ 2 × 10^24 cm-2 is present
XMM-Newton broad-band observations of NGC 7582: N{H} variations and fading out of the active nucleus
No full textThe early stage of a cosmic collision? XMM-Newton unveils two obscured AGN in the galaxy pair ESO509-IG066
No full textWe report the XMM-Newton discovery of a X-ray bright AGN pair in the interacting galaxy system ESO509-IG066. Both galaxies host an X-ray luminous ( L-X similar to 10(43) erg s(-1)) obscured nucleus with column densities N-H similar or equal to 7 x 10(22) cm(-2) and N-H similar or equal to 5 x 10(21) cm(-2). The optical morphology is only mildly disturbed, suggesting a merging system in the early stage of its evolution. Still, the pair is probably gravitationally bound, and might eventually evolve into a compact, fully gas embedded systems such as NGC 6240 ( Komossa et al. 2003)
Unified properties of supermassive black hole winds in radio-quiet and radio-loud AGN
Full text linkPowerful supermassive black hole (SMBH) winds in the form of ultra-fast outflows (UFOs) are detected in the X-ray spectra of several active galactic nuclei (AGNs) seemingly independently of their radio classification between radio quiet (RQ) and radio loud (RL). In this work, we explore the physical parameters of SMBH winds through a uniform analysis of a sample of X-ray bright RQ and RL AGN. We explored several correlations between different wind parameters and with respect to the AGN bolometric and Eddington luminosities. Our analysis shows that SMBH winds are not only a common trait of both AGN classes but also that they are most likely produced by the same physical mechanism. Consequently, we find that SMBH winds do not follow the radio-loudness dichotomy seen in jets. On average, a comparable amount of material accreted by the SMBH is ejected through such winds. The average wind power corresponds to about 3 per cent of the Eddington luminosity, confirming that they can drive AGN feedback. Moreover, the most energetic outflows are found in the most luminous sources. We find a possible positive correlation of the wind energetics, renormalized to the Eddington limit, with respect to λEdd, consistent with the correlation found with bolometric luminosity. We also observe a possible positive correlation between the energetics of the outflow and the X-ray radio-loudness parameter. In general, these results suggest an underlying relation between the acceleration mechanisms of accretion disc winds and jets
Unified properties of supermassive black hole winds in radio-quiet and radio-loud AGN
Full text linkPowerful supermassive black hole (SMBH) winds in the form of ultra-fast outflows (UFOs) are detected in the X-ray spectra of several active galactic nuclei (AGNs) seemingly independently of their radio classification between radio quiet (RQ) and radio loud (RL). In this work, we explore the physical parameters of SMBH winds through a uniform analysis of a sample of X-ray bright RQ and RL AGN. We explored several correlations between different wind parameters and with respect to the AGN bolometric and Eddington luminosities. Our analysis shows that SMBH winds are not only a common trait of both AGN classes but also that they are most likely produced by the same physical mechanism. Consequently, we find that SMBH winds do not follow the radio-loudness dichotomy seen in jets. On average, a comparable amount of material accreted by the SMBH is ejected through such winds. The average wind power corresponds to about 3 per cent of the Eddington luminosity, confirming that they can drive AGN feedback. Moreover, the most energetic outflows are found in the most luminous sources. We find a possible positive correlation of the wind energetics, renormalized to the Eddington limit, with respect to λEdd, consistent with the correlation found with bolometric luminosity. We also observe a possible positive correlation between the energetics of the outflow and the X-ray radio-loudness parameter. In general, these results suggest an underlying relation between the acceleration mechanisms of accretion disc winds and jets
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
