1,206 research outputs found
A comprehensive X-ray view of the active nucleus in NGC 4258
(Abridged) We present a detailed broadband X-ray spectrum of NGC 4258, with
the goal of precisely measuring the coronal luminosity and accretion flow
properties of the AGN, and track any possible variation across two decades of
observations. We collect archival XMM-Newton, Chandra, Swift/BAT and NuSTAR
spectroscopic observations spanning 15 years, and fit them with a suite of
state of the art models, including a warped disk model which is suspected to
provide the well known obscuration observed in the X-rays. We complement this
information with archival results from the literature. Clear spectral
variability is observed among the different epochs. The obscuring column
density shows possibly periodic fluctuations on a timescale of 10 years, while
the intrinsic luminosity displays a long term decrease of a factor of three in
a time span of 15 years (from erg s
in the early 2000s, to erg s
in 2016). The average absorption-corrected X-ray luminosity
, combined with archival determinations of the bolometric
luminosity, implies a bolometric correction , intriguingly
typical for Seyferts powered by accretion through geometrically thin,
radiatively efficient disks. Moreover, the X-ray photon index is
consistent with the typical value of the broader AGN population. However, the
accretion rate in Eddington units is very low, well within the expected RIAF
regime. Our results suggest that NGC 4258 is a genuinely low-luminosity Seyfert
II, with no strong indications in its X-ray emission for a hot, RIAF-like
accretion flow.Comment: Accepted for publication in A&A. 14 pages, 6 figures, 3 table
Coherent Diffraction Radiation experiment at CTF3—Simulation studies
A two-target model was developed for the simulations of Coherent Diffraction Radiation (CDR) phenomenon for the experiment at the CLIC Test Facility 3 (CTF3 at CERN). The model is based on a classical DR theory. The radiation distribution from the targets, as a function of the angle and the frequency, was calculated for the first and the second target separately in order to understand how the final radiation distribution from the two targets, working as a system, is formed. The final radiation distribution of destructive interference between the two targets was obtained as well. The distributions were calculated for the working parameters of both the CTF3 and the experimental setup and were used for a single-electron spectrum calculation, required for the bunch profile reconstruction
Comments on “Ochratoxin A: In utero Exposure in Mice Induces Adducts in Testicular DNA. Toxins 2010, 2, 1428–1444”—Mis-Citation of Rat Literature to Justify a Hypothetical Role for Ochratoxin A in Testicular Cancer
A manuscript in the journal recently cited experimental rat data from two manuscripts to support plausibility of a thesis that ochratoxin A might be a cause of human testicular cancer. I believe that there is no experimental evidence that ochratoxin A produces testicular cancer in rats or mice
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