11,247 research outputs found
Corehead Orchard Tree Establishment and Grazing Damage Survey 2013: Report to the Borders Forest Trust
The research report describes the history of fruit orchards in Scotland and monitoring of efforts to establish a traditional fruit orchard. Comparisons are made of the performance of different fruit varieties during the first two years of growth and the effects of deer browsing are discussed
The reprocessing features in the X-ray spectrum of the NELG MCG-5-23-16
We present results from the spectral analysis of the Seyfert 1.9 galaxy
MCG-5-23-16, based on ASCA, BeppoSAX, Chandra and XMM-Newton observations. The
spectrum of this object shows a complex iron Kalpha emission line, which is
best modeled by a superposition of a narrow and a broad (possibly relativistic)
iron line, together with a Compton reflection component. Comparing results from
all (six) available observations, we do not find any significant variation in
the flux of both line components. The moderate flux continuum variability
(about 25% difference between the brightest and faintest states), however, does
not permit us to infer much about the location of the line-emitting material.
The amount of Compton reflection is lower than expected from the total iron
line EW, implying either an iron overabundance or that one of the two line
components (most likely the narrow one) originates in Compton-thin matter.Comment: Accepted for publication in A&
X-ray imaging of the Seyfert 2 galaxy Circinus with Chandra
We present results from the zeroth-order imaging of a Chandra HETGS
observation of the nearby Seyfert 2 galaxy Circinus. Twelve X-ray sources were
detected in the ACIS-S image of the galaxy, embedded in diffuse X-ray emission.
The latter shows a prominent (~18arcsec) soft ``plume'' in the N-W direction,
coincident with the [OIII] ionization cone. The radial profiles of the
brightest X-ray source at various energies are consistent with an unresolved
(FWHM ~0.8arcsec) component, which we identify as the active nucleus, plus two
extended components with FWHMs ~ 2.3arcsec and 18arcsec, respectively. In a
radius of 3arcsec, the nucleus contributes roughly the same flux as the
extended components at the softest energies (< 2 keV). However, at harder
energies (> 2 keV), the contribution of the nucleus is dominant. The
zeroth-order ACIS spectrum of the nucleus exhibits emission lines at both soft
and hard X-rays, including a prominent Fe Kalpha line at 6.4 keV, showing that
most of the X-ray lines previously detected with ASCA originate in a compact
region (<15 pc). Based on its X-ray spectrum, we argue that the 2.3arcsec
extended component is scattered nuclear radiation from nearby ionized gas. The
large-scale extended component includes the emission from the N-W plume and
possibly from the outer starburst ring.Comment: Figure 1 in color. ApJ Letters, in pres
X-ray reprocessing in Seyfert Galaxies: simultaneous XMM-Newton/BeppoSAX observations
We selected a sample of eight bright unobscured (at least at the iron line
energy) Seyfert Galaxies observed simultaneously by XMM-Newton and BeppoSAX,
taking advantage of the complementary characteristics of the two missions. The
main results of our analysis can be summarized as follows: narrow neutral iron
lines are confirmed to be an ubiquitous component in Seyfert spectra; none of
the analyzed sources shows unambiguously a broad relativistic iron line; all
the sources of our sample (with a single exception) show the presence of a
Compton reflection component; emission lines from ionized iron are observed in
some sources; peculiar weak features around 5-6 keV (possibly arising from
rotating spots on the accretion disk) are detected in two sources. The scenario
emerging from these results strongly requires some corrections for the
classical model of reprocessing from the accretion disk. As for materials
farther away from the Black Hole, our results represent a positive test for the
Unification Model, suggesting the presence of the torus in (almost) all
sources, even if unobscured.Comment: Accepted for publication in A&
The Suzaku X-ray spectrum of NGC 3147. Further insights on the best "true" Seyfert 2 galaxy candidate
NGC 3147 is so far the most convincing case of a "true" Seyfert 2 galaxy,
i.e. a source genuinely lacking the Broad Line Regions. We obtained a Suzaku
observation with the double aim to study in more detail the iron line complex,
and to check the Compton-thick hypothesis for the lack of observed optical
broad lines.
The Suzaku XIS and HXD/PIN spectra of the source were analysed in detail. The
line complex is composed of at least two unresolved lines, one at about 6.45
keV and the other one at about 7 keV, most likely identified with Fe XVII/XIX,
the former, and Fe XXVI, the latter. The high-ionization line can originate
either in a photoionized matter or in an optically thin thermal plasma. In the
latter case, an unusually high temperature is implied. In the photoionized
model case, the large equivalent width can be explained either by an extreme
iron overabundance or by assuming that the source is Compton-thick. In the
Compton-thick hypothesis, however, the emission above 2 keV is mostly due to a
highly ionized reflector, contrary to what is usually found in Compton-thick
Seyfert 2s, where reflection from low ionized matter dominates. Moreover, the
source flux varied between the XMM-Newton and the Suzaku observations, taken
3.5 years apart, confirming previous findings and indicating that the size of
the emitting region must be smaller than a parsec.
The hard X-ray spectrum is also inconclusive on the Compton-thick hypothesis.
Weighting the various arguments, a "true" Seyfert 2 nature of NGC 3147 seems to
be still the most likely explanation, even if the "highly ionized reflector"
Compton-thick hypothesis cannot at present be formally rejected.Comment: 6 pages, accepted for publication in Astronomy & Astrophysic
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