1,721,475 research outputs found
The properties of the absorbing and line-emitting material in IGR J16318-4848
No full textWe have performed a detailed analysis of the XMM-Newton observation of IGR J16318-4848, to study the properties of the matter responsible for the obscuration and for the emission of Fe and Ni lines. Even if the line-of-sight material has a column density of about 2x10(24) m(-2), from the Fe Kalpha line EW and Compton Shoulder we argue that the matter should have an average column density of a few x10(23) cm(-2), along with a covering factor of about 0.1-0.2. The iron Kalpha line varies on time-scales as short as 1000 s, implying a size of the emitting region smaller than about 3x10(13) cm. The flux of the line roughly follows the variations of the continuum, but not exactly, suggesting a variation of the geometrical properties of the emitting region on similar time-scales
The properties of the absorbing and line emitting material in IGR J16318-4848
No full textWe analyzed the 2003 Target of Opportunity XMM-Newton observation of IGR J16318-4848, to derive the properties of the matter responsible for the obscuration and for the emission of Fe and Ni lines. The line of sight material has a column density of about 2 x 10(24) cm(-2) but, from the Fe K alpha line EW and Compton Shoulder, we argue that the average column density is a few x 10(23) cm(-2), while the covering factor is about 0.1-0.2. The iron K alpha line varies on time scales as short as 1000 s, implying a size of the emitting region less than 3 x 10(13) cm. An ongoing XMM-Newton/INTEGRAL monitoring campaign is confirming the non-transient nature of the source
On the origin of soft X-rays in obscured AGN: answers from high-resolution spectroscopy with XMM-Newton
No full textThe XMM-Newton long look of NGC 1365: uncovering of the obscured X-ray source
No full textWe present an analysis of the extreme obscuration variability observed during an XMM–Newton 5-d continuous monitoring of the active galactic nuclei (AGN) in NGC 1365. The source was in a reflection-dominated state in the first ∼1.5 d, then a strong increase in the 7–10 keV emission was observed in ∼10 h, followed by a symmetric decrease. The spectral analysis of the different states clearly shows that this variation is due to an uncovering of the X-ray source. From this observation, we estimate a size of the X-ray source DS < 1013 cm, a distance of the obscuring clouds R∼ 1016 cm and a density n∼ 1011 cm−3. These values suggest that the X-ray absorption/reflection originates from the broad-line region clouds. This is also supported by the resolved width of the iron narrow Kα emission line, consistent with the width of the broad Hβ line
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
The soft X-ray/NLR connection: a single photoionized medium?
No full textWe present a sample of 8 nearby Seyfert 2 galaxies observed by HST and Chandra. All of the sources present soft X-ray emission which is coincident in extension and overall morphology with the [O ii
The BeppoSAX X-ray view of reflection-dominated Seyfert galaxies
No full textWe present new results from BeppoSAX observations of reflection-dominated Seyfert galaxies, and namely: 1) the Compton-thick Seyfert 2 NGC 1068 and Circinus Galaxy; 2) the Seyfert 1 NGC 4051, whose nucleus was observed on May 1998 to have switched off, leaving only a residual reflection component as an echo of its past activity. Our main focus in this paper is on the soft X-ray continuum properties and on the X-ray line spectroscopy. (C) 2000 COSPAR. Published by Elsevier Science Ltd
Changing look: from Compton-thick to Compton-thin, or the rebirth of fossil active galactic nuclei
No full textWe discuss the properties of a small sample of type 2 Seyfert galaxies whose X-ray spectra changed appearance on time-scales of years, becoming reflection-dominated from Compton-thin, or vice versa. A reflection-dominated spectrum is usually taken as evidence of Compton-thick absorption, but we instead argue that such a spectrum is due to a temporary switching-off of the nuclear radiation. The observations discussed here may help to explain mismatches between optical and X-ray classifications, and provide new strong and direct evidence for the presence of more than one cold circumnuclear region in type 2 Seyfert galaxies
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