1,721,651 research outputs found
Extended Corona Models of X-ray Reverberation in the AGN 1H 0707-495 and IRAS 13224-3809
No full textWe fit a new vertically extended corona model to previously measured reverberation time lags observed by XMM–Newton in two extremely variable narrow-line Seyfert 1 active galactic nuclei, 1H 0707−495 and IRAS 13224−3809, in a variety of similarly observed flux groups and explore the model in all observations over a 16 yr period. The model employs two X-ray sources located along the black hole rotational axis at height, h1 and h2, respectively. These sources have their associated photon indices Γ1 and Γ2 which respond to fluctuations in the disc with a maximum response duration of tmax and a propagation delay between the response of the two of tshift. We find that for 1H 0707−495, h2 is significantly correlated with Γ1 and anticorrelated with ionization ξ. Whilst the 1H 0707−495 corona extends upwards, the emission appears softer and the disc is less ionized. We find similarities in IRAS 13224−3809, but significant anticorrelation between Γ2 and both tmax and tshift. This suggests that when the IRAS 13224−3809 corona becomes softer while extending vertically upwards, the overall corona response occurs faster. This may also suggest that the inner disc also becomes more active. In addition, Γ1 and Γ2 are extreme, relatively less variable, but more separate in IRAS 13224−3809 than in 1H 0707−495. This suggests that the IRAS 13224−3809 corona may be more patchy in the sense that it has two more clear distinct spectral zones of Γ1 and Γ2 (possibly relating to two distinct zones of coronal temperature) when compared to 1H 0707−495
Blueshifted absorption lines from X-ray reflection in IRAS 13224-3809
Get PDFWe explore a disc origin for the highly blueshifted, variable absorption lines seen in the X-ray spectrum of the narrow-line Seyfert 1 galaxy IRAS 13224-3809. The blueshift corresponds to a velocity of ∼0.25c. Such features in other active galactic nuclei are often interpreted as ultrafast outflows. The velocity is of course present in the orbital motions of the inner disc. The absorption lines in IRAS 13224-3809 are best seen when the flux is low and the reflection component of the disc is strong relative to the power-law continuum. The spectra are consistent with a model in which the reflection component passes through a thin, highly ionized absorbing layer at the surface of the inner disc, the blueshifted side of which dominates the flux due to relativistic aberration (the disc inclination is about 70°). No fast outflow need occurs beyond the disc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Relativistic spectroscopy of the extreme NLS1 IRAS 13224
No full textI will review results from the 2016 observing campaign on the most X-ray variable AGN, IRAS 13224. This source shows both extreme relativistic reflection from the inner accretion disk and an ultra-fast outflow, both variable on timescales of under an hour. As no other absorption features are present in the spectrum, we have a clean view of the inner accretion disk and the relativistic physics exhibited there. I will also discuss the implications of these results, and potential next steps for expanding our knowledge of accretion and outflows using NLS1s.</p
XMM-Newton Observations of the Narrow-Line Seyfert 1 Galaxy IRAS 132243809 : X-ray Spectral Analysis II
No full textPreviously, we modelled the X-ray spectra of the narrow-line Seyfert 1 galaxy
IRAS 132243809 using a disc reflection model with a fixed electron density
of cm. An additional blackbody component was required to fit
the soft X-ray excess below 2 keV. In this work, we analyse simultaneously five
flux-resolved XMM-Newton spectra of this source comprising data collected over
2 Ms. A disc reflection model with an electron density of cm and an iron abundance of is used to fit the broad-band spectra of this source.
No additional component is required to fit the soft excess. Our best-fit model
provides consistent measurements of black hole spin and disc inclination angle
as in previous models where a low disc density was assumed. In the end, we
calculate the average illumination distance between the corona and the
reflection region in the disc of IRAS 132243809 based on best-fit density
and ionisation parameters, which changes from 0.43 in the lowest flux state to 1.71 in the highest flux state assuming a black hole mass of
. is the ratio between the
flux of the coronal emission that reaches the accretion disc and infinity. This
ratio depends on the geometry of the coronal region in IRAS 132243809. So we
only discuss its value based on the simple `lamp-post' model, although detailed
modelling of the disc emissivity profile of IRAS 132243809 is required in
future to reveal the exact geometry of the corona.Comment: 17 pages, 15 figures including appendices; accepted for publication
in MNRA
Variations on the Author
Get PDF“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
Get PDFWe 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
Is there a UV/X-ray connection in IRAS 13224-3809 question mark
No full textPublished versionWe present results from the optical, ultraviolet, and X-ray monitoring of the NLS1 galaxy IRAS 13224−3809 taken with Swift and XMM–Newton during 2016. IRAS 13224−3809 is the most variable bright AGN in the X-ray sky and shows strong X-ray reflection, implying that the X-rays strongly illuminate the inner disc. Therefore, it is a good candidate to study the relationship between coronal X-ray and disc UV emission. However, we find no correlation between the X-ray and UV flux over the available ∼40 d monitoring, despite the presence of strong X-ray variability and the variable part of the UV spectrum being consistent with irradiation of a standard thin disc. This means either that the X-ray flux which irradiates the UV emitting outer disc does not correlate with the X-ray flux in our line of sight and/or that another process drives the majority of the UV variability. The former case may be due to changes in coronal geometry, absorption or scattering between the corona and the disc
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