1,721,115 research outputs found
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
A hard medium survey with ASCA III. a Type 2 AGN revealed from X-ray spectroscopy
No full textIn this paper we report the discovery of a hard Xray selected Type 2 Seyfert galaxy and we present and discuss its X-ray and optical spectrum together with the radio to X-ray energy distribution. The X-ray source - AXJ2254+1146 - is part of the ASCA Hard Serendipitous Survey (HSS). What makes this discovery particularly noteworthy is the fact that the Spe 2 classification of this Seyfert galaxy has resulted directly from the X-ray data and has been confirmed by optical spectroscopy only subsequently. The X-ray spectrum of AXJ2254+1146 is best described by a model consisting of an unresolved Gaussian line at 6.43 +/- 0.1 keV plus the so called "leaky-absorber" continua having an intrinsic power law photon index of Gamma = 2.51(2.17)(2.76) (1 sigma confidence interval). The best fit values of the absorbing column density (N-H = 1.85(1.47)(2.24) x 10(23) cm(-2)), of the line equivalent width (0.6(0.36)(0.84) keV) and of the scattering fraction (0.7(0.1)(1.4)%), lead us to classify it as a Type 2 AGN from an X-ray point of view. Inspection of the POSS II image reveals the presence, within the ASCA X-ray error circle, of the nearby Sbc spiral galaxy UGC 12237 (m(Bo) = 14.26) that, even on positional ground considerations alone, is the most likely optical counterpart of AXJ2254+1146. Subsequent optical spectroscopy of UGC 12237 has confirmed its Seyfert 2 optical nature
X-Ray Evidence for the Accretion Disc-Outflow Connection in 3C 111
Full text linkWe present the spectral analysis of three Suzaku X-ray Imaging Spectrometer observations of 3C III requested to monitor the predicted variability of its ultrafast outflow on approximately 7 d time-scales. We detect an ionized iron emission line in the first observation and a blueshifted absorption line in the second, when the flux is approximately 30 per cent higher. The location of the material is constrained at less than 0.006 pc from the variability. Detailed modelling supports an identification with ionized reflection off the accretion disc at approximately 20-100rg from the black hole and a highly ionized and massive ultrafast outflow with velocity approximately 0.1c, respectively. The outflow is most probably accelerated by radiation pressure, but additional magnetic thrust cannot be excluded. The measured high outflow rate and mechanical energy support the claims that disc outflows may have a significant feedback role. This work provides the first direct evidence for an accretion disc-outflow connection in a radio-loud active galactic nucleus, possibly linked also to the jet activity
The High Energy view of the Broad Line Radio Galaxy 3C 111
No full text14 páginas, 9 figuras, 5 tablas.-- El Pdf del artículo es la versión pre-print: arXiv:1108.2609v1.-- et al.We present the analysis of Suzaku and XMM–Newton observations of the broad-line radio
galaxy (BLRG) 3C 111. Its high-energy emission shows variability, a harder continuum with
respect to the radio-quiet active galactic nucleus population, and weak reflection features.
Suzaku found the source in a minimum flux level; a comparison with the XMM–Newton data
implies an increase of a factor of 2.5 in the 0.5–10 keV flux, in the 6 months separating the
two observations. The iron K complex is detected in both data sets, with rather low equivalent
width(s). The intensity of the ironKcomplex does not respond to the change in continuum flux.
An ultrafast, high-ionization outflowing gas is clearly detected in the Suzaku/X-ray Imaging
Spectrometer data; the absorber is most likely unstable. Indeed, during the XMM–Newton
observation, which was 6 months after, the absorber was not detected. No clear rollover in
the hard X-ray emission is detected, probably due to the emergence of the jet as a dominant
component in the hard X-ray band, as suggested by the detection above ∼100 keV with the
GSO onboard Suzaku, although the present data do not allow us to firmly constrain the relative
contribution of the different components. The fluxes observed by the γ -ray satellites CGRO
and Fermi would be compatible with the putative jet component if peaking at energies E ∼ 100MeV. In the X-ray band, the jet contribution to the continuum starts to be significant only
above 10 keV. If the detection of the jet component in 3C 111 is confirmed, then its relative
importance in the X-ray energy band could explain the different observed properties in the
high-energy emission of BLRGs, which are otherwise similar in their other multiwavelength
properties. Comparison between X-ray and γ -ray data taken at different epochs suggests that
the strong variability observed for 3C 111 is probably driven by a change in the primary
continuum.LB acknowledges support from the Spanish Ministry of Science and
Innovation through a ‘Juan de la Cierva’ fellowship. Financial support
for this work was provided by the Spanish Ministry of Science
and Innovation, through research grant AYA2009-08059.Peer reviewe
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
X-ray absorption variability in NGC 4507
No full text"We present a complete spectral analysis of an XMM-Newton and Chandra campaign of the obscured AGN in NGC 4507, consisting of six observations spanning a period of six months, ranging from 2010 June to December. We detect strong absorption variability on time-scales between 1.5 and 4 months, suggesting that the obscuring material consists of gas clouds at parsec-scale distance. The lack of significant variability on shorter time-scales suggests that this event is not due to absorption by broad-line region (BLR) clouds, which was instead found in other studies of similar sources. This shows that a single, universal structure of the absorber (either BLR clouds, or the parsec-scale torus) is not enough to reproduce the observed complexity of the X-ray absorption features of this AGN.
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
The Suzaku view of highly-ionised outflows in AGN: I - Statistical detection and global absorber properties
No full textWe present the results of a new spectroscopic study of Fe K-band absorption in Active Galactic Nuclei (AGN). Using data obtained from the Suzaku public archive we have performed a statistically driven blind search for Fe XXV Hea and/or Fe XXVI Lyb absorption lines in a large sample of 51 type 1.0-1.9 AGN. Through extensive Monte Carlo simulations we find statistically significant absorption is detected at E>6.7 keV in 20/51 sources at the P(MC)>95% level, which corresponds to ~40% of the total sample. In all cases, individual absorption lines are detected independently and simultaneously amongst the two (or three) available XIS detectors which confirms the robustness of the line detections. The most frequently observed outflow phenomenology consists of two discrete absorption troughs corresponding to Fe XXV Hea and Fe XXVI Lyb at a common velocity shift. From xstar fitting the mean column density and ionisation parameter for the Fe K absorption components are log(NH/cm^{-2})~23 and log(xi/erg cm s^{-1})~4.5, respectively. Measured outflow velocities span a continuous range from <1,500 km/s up to ~100,000 km/s, with mean and median values of ~0.1c and ~0.056c, respectively. The results of this work are consistent with those recently obtained using XMM-Newton and independently provides strong evidence for the existence of very highly-ionised circumnuclear material in a significant fraction of both radio-quiet and radio-loud AGN in the local universe
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
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