411 research outputs found
Duchenne and Becker muscular dystrophy prevalence in South Africa and molecular findings in 128 persons affected
A genetic service for Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) was initiated in Cape Town in 1987. Of the 143 DMD patients diagnosed during the period 1987-1992, 66 had a familial pattern of inheritance and 77 were apparently sporadic. Twenty BMD patients were identified, of whom 12 had other affected relatives and 8 were sporadic. Overall minimum prevalence rates of 1/100 000 for DMD and 1/55 000 for BMD were calculated. A markedly low DMD prevalence in the indigenous black population (1/250000) contributed tothe overall low DMD prevalence in South Africa when compared with that in the UK (1/40 000).By means of molecular methods, the diagnosis in 42% of the affected DMD males was confirmed by detection of deletions in the dystrophin gene. Deletions were identified in 50% of Indian, white and mixed ancestry patients. In contrast, only 22% of blacks had identifiable deletions.DMD appears to be underrepresented in the black population; the low deletion frequency in this group suggests that unique mutations not detectable by methods used in this study may be more frequent in these patients than in the other populations. The increased DMD frequency in Indians corroborates findings reported from the UK
Proving strong magnetic fields near to the central black hole in the quasar PG0043+039 via cyclotron lines
The optical luminous quasar PG0043+039 has not been detected before in deep
X-ray observations indicating the most extreme optical-to-X-ray slope index
of all quasars. This study aims to detect PG0043+039 in a deep
X-ray exposure. Furthermore, we wanted to check out whether this object shows
specific spectral properties in other frequency bands. We took deep X-ray
(XMM-Newton), far-ultraviolet (HST), and optical (HET, SALT telescopes) spectra
of PG0043+039 simultaneously in July 2013. We just detected PG0043+039 in our
deep X-ray exposure. The steep gradient is
consistent with an unusual steep gradient with
seen in the UV/far-UV continuum. The optical/UV
continuum flux has a clear maximum near 2500 {\AA}. The UV spectrum is very
peculiar because it shows broad humps in addition to known emission lines. A
modeling of these observed humps with cyclotron lines can explain their
wavelength positions, their relative distances, and their relative intensities.
We derive plasma temperatures of T 3keV and magnetic field strengths
of B 2 G for the line-emitting regions close to the
black hole.Comment: 4 pages, 3 figures, Astronomy & Astrophysics in pres
A long hard look at the minimum state of PG 2112+059 with XMM-Newton
XMM-Newton successfully detected the minimum state of PG 2112+059 during a
short snapshot observation and performed a long follow-up observation. The high
signal-to-noise spectra are modelled assuming different emission scenarios and
compared with archival spectra taken by XMM-Newton and Chandra.
The PG 2112+059 X-ray spectra acquired in May 2007 allowed the detection of a
weak iron fluorescent line, which is interpreted as being caused by reflection
from neutral material at some distance from the primary X-ray emitting source.
The X-ray spectra of PG 2112+059 taken at five different epochs during
different flux states can be interpreted within two different scenarios. The
first consists of two layers of ionised material with column densities of N_H
~5 x 10^22 cm^-2 and N_H ~3.5 x 10^23 cm^-2, respectively. The first layer is
moderately ionised and its ionisation levels follow the flux changes, while the
other layer is highly ionised and does not show any correlation with the flux
of the source. The spectra can also be interpreted assuming reflection by an
ionised accretion disk seen behind a warm absorber. The warm absorber
ionisation is consistent with being correlated with the flux of the source,
which provides an additional degree of self-consistency with the overall
reflection-based model. We explain the spectral variability with light bending
according to the models of Miniutti and Fabian and constrain the black hole
spin to be a/M > 0.86. Both scenarios also assume that a distant cold reflector
is responsible for the Fe K \alpha emission line.
Light bending provides an attractive explanation of the different states of
PG 2112+059 and may also describe the physical cause of the observed properties
of other X-ray weak quasars.Comment: 15 pages, 12 figures, A&A latex, accepted for publication in
Astronomy & Astrophysic
The structure of the X-ray absorber in Mrk 915 revealed by Swift
In this paper we present the results obtained with a monitoring programme (23
days long) performed with Swift-XRT on the local Seyfert galaxy Mrk 915. The
light-curve analysis shows a significant count rate variation (about a factor
of 2-3) on a time-scale of a few days, while the X-ray colours show a change in
the spectral curvature below 2 keV and the presence of two main spectral
states. From the spectral analysis we find that the observed variations can be
explained by the change of the intrinsic nuclear power (about a factor of 1.5)
coupled with a change of the properties of an ionized absorber. The quality of
the data prevents us from firmly establishing if the spectral variation is due
to a change in the ionization state and/or in the covering factor of the
absorbing medium. The latter scenario would imply a clumpy structure of the
ionized medium. By combining the information provided by the light curve and
the spectral analyses, we can derive some constraints on the location of the
absorber under the hypotheses of either homogeneous or clumpy medium. In both
cases, we find that the absorber should be located inside the outer edge of an
extended torus and, in particular, under the clumpy hypothesis, it should be
located near, or just outside, to the broad emission line region.Comment: 8 pages, 6 figures, 1 table. Accepted for publication on MNRA
XMM-Newton and NuSTAR joint observations of Mrk 915: a deep look into the X-ray properties
We report on the X-ray monitoring programme (covering slightly more than 11
days) carried out jointly by XMM-Newton and NuSTAR on the intermediate Seyfert
galaxy Mrk 915. The light curves extracted in different energy ranges show a
variation in intensity but not a significant change in spectral shape. The
X-ray spectra reveal the presence of a two-phase warm absorber: a fully
covering mildly ionized structure [log xi/(erg cm/s)~2.3, NH~1.3x10^21 cm-2]
and a partial covering (~90 per cent) lower ionized one [log xi/(erg cm/s)~0.6,
NH~2x10^22 cm-2]. A reflection component from distant matter is also present.
Finally, a high-column density (NH~1.5x10^23 cm-2) distribution of neutral
matter covering a small fraction of the central region is observed, almost
constant, in all observations. Main driver of the variations observed between
the datasets is a decrease in the intrinsic emission by a factor of ~1.5.
Slight variations in the partial covering ionized absorber are detected, while
the data are consistent with no variation of the total covering absorber. The
most likely interpretation of the present data locates this complex absorber
closer to the central source than the narrow line region, possibly in the broad
line region, in the innermost part of the torus, or in between. The neutral
obscurer may either be part of this same stratified structure or associated
with the walls of the torus, grazed by (and partially intercepting) the line of
sight.Comment: 14 pages, 10 figures, 4 tables. Accepted for publication in MNRA
X-ray observation of ULAS J1120+0641, the most distant quasar at z=7.08
We aim at probing the emission mechanism of the accreting super massive black
holes in the high redshift Universe. We study the X-ray spectrum of
ULAS1120+0641, the highest redshift quasar detected so far at z=7.085, which
has been deeply observed (340 ks) by XMM-Newton. Despite the long integration
time the spectral analysis is limited by the poor statistics, with only 150
source counts being detected. We measured the spectrum in the 2-80 keV
rest-frame (0.3-10 keV observed) energy band. Assuming a simple power law model
we find a photon index of 2.0+/-0.3 and a luminosity of 6.7+/-0.3 10^44 erg/s
in the 2-10 keV band, while the intrinsic absorbing column can be only loosely
constrained (NH< 1E23 cm^-2). Combining our data with published data we
calculate that the X-ray-to-optical spectral index alpha_OX is1.8+/-0.1, in
agreement with the alpha_OX-UV luminosity correlation valid for lower redshift
quasars. We expanded to high energies the coverage of the spectral energy
distribution of ULAS1120+0641. This is the second time that a z >6 quasar has
been investigated through a deep X-ray observation. In agreement with previous
studies of z~6 AGN samples, we do not find any hint of evolution in the
broadband energy distribution. Indeed from our dataset ULAS 1120+0641 is
indistinguishable from the population of optically bright quasar at lower
redshift.Comment: 5 pages, 4 figures, A&A in press; updated with the accepted versio
Mining the XRT archive to probe the X-ray absorber structure in the AGN population
One of the key ingredients of the Unified Model of Active Galactic Nuclei
(AGN) is the presence of a torus-like optically thick medium composed by dust
and gas around the putative supermassive black hole. However, the structure,
size and composition of this circumnuclear medium are still matter of debate.
To this end, the search for column density variations through X-ray monitoring
on different timescales (months, weeks and few days) is fundamental to
constrain size, kinematics and location of the X-ray absorber(s). Here we
describe our project of mining the Swift-XRT archive to assemble a sample of
AGN with extreme column density variability and determining the physical
properties of the X-ray absorber(s). We also present the results obtained from
a daily-weekly Swift-XRT follow-up monitoring recently performed on one of the
most interesting new candidates for variability discovered so far, Mrk 915.Comment: 6 pages, 3 figures. To appear in Proceedings of Science for the
"Swift: 10 years of Discovery" meeting, held in Rome (2-5 December 2014
NuSTAR reveals that the heavily obscured nucleus of NGC 2785 was the contaminant of IRAS 09104+4109 in the BeppoSAX/PDS hard X-rays
The search for heavily obscured active galactic nuclei (AGNs) has been
revitalized in the last five years by NuSTAR, which has provided a good census
and spectral characterization of a population of such objects, mostly at low
redshift, thanks to its enhanced sensitivity above 10 keV compared to previous
X-ray facilities, and its hard X-ray imaging capabilities. We aim at
demonstrating how NGC2785, a local (z=0.009) star-forming galaxy, is
responsible, in virtue of its heavily obscured active nucleus, for significant
contamination in the non-imaging BeppoSAX/PDS data of the relatively nearby
(~17 arcmin) quasar IRAS 09104+4109 (z=0.44), which was originally
mis-classified as Compton thick. We analyzed ~71 ks NuSTAR data of NGC2785
using the MYTorus model and provided a physical description of the X-ray
properties of the source for the first time. We found that NGC2785 hosts a
heavily obscured (NH~3*10^{24} cm^{-2}) nucleus. The intrinsic X-ray luminosity
of the source, once corrected for the measured obscuration (L(2-10 keV)~10^{42}
erg/s), is consistent within a factor of a few with predictions based on the
source mid-infrared flux using widely adopted correlations from the literature.
Based on NuSTAR data and previous indications from the Neil Gehrels Swift
Observatory (BAT instrument), we confirm that NGC2785, because of its hard
X-ray emission and spectral shape, was responsible for at least one third of
the 20-100 keV emission observed using the PDS instrument onboard BeppoSAX,
originally completely associated with IRAS 09104+4109. Such emission led to the
erroneous classification of this source as a Compton-thick quasar, while it is
now recognized as Compton thin.Comment: Six pages, 3 figures, A&A, in pres
The XMM-Newton view of the relativistic spectral features in AXJ0447-0627
The XMM-Newton observation of the optically Type 1 AGN AXJ0447-0627 (z=0.214)
unambiguously reveals a complex, bright and prominent set of lines in the 4-8
keV rest frame energy range. Although, from a phenomenological point of view,
the observed properties can be described by a simple power law model plus 5
narrow Gaussian lines (at rest frame energies of nearly 4.49, 5.55, 6.39, 7.02
and 7.85 keV), we find that a model comprising a power law (Gamma of the order
of 2.2), a reflected relativistic continuum, a narrow Fe I Kalpha line from
neutral material as well as a broad Fe Kalpha relativistic line from a ionized
accretion disk represents a good physical description of the data. The ''double
horned'' profile of the relativistic line implies an inclination of the
accretion disk of the order of 45 degree, and an origin in a narrow region of
the disk, from R_in of the order of 19 GM/c^2 to R_out of the order of 30
GM/c^2. The narrow Fe I Kalpha line from neutral material is probably produced
far from the central black hole, most likely in the putative molecular torus.
Although some of these properties have been already found in other Type 1 AGN
and discussed in the literature, at odd with the objects reported so far we
measure high equivalent widths (EWs) of the observed lines: nearly 1.4 keV for
the ``double horned'' relativistic line and nearly 0.4 keV for the narrow line.Comment: 16 pages, 3 figures, Latex manuscript; accepted for publication in
Ap
WISE colours and star-formation in the host galaxies of radio-loud narrow-line Seyfert 1
We investigate the mid-infrared properties of the largest (42 objects) sample
of radio-loud narrow-line Seyfert 1 (RL NLS1) collected to date, using data
from the Wide-field Infrared Survey Explorer (WISE). We analyse the mid-IR
colours of these objects and compare them to what is expected from different
combinations of AGN and galaxy templates. We find that, in general, the
host-galaxy emission gives an importan contribution to the observed mid-IR flux
in particular at the longest wavelengths (W3, at 12micron, and W4, at
22micron). In about half of the sources (22 objects) we observe a very red
mid-IR colour (W4-W3>2.5) that can be explained only using a starburst galaxy
template (M82). Using the 22micron luminosities, corrected for the AGN
contribution, we have then estimated the star-formation rate for 20 of these
"red" RL NLS1, finding values ranging from 10 to 500 Msun/y. For the RL NLS1
showing bluer colours, instead, we cannot exclude the presence of a
star-forming host galaxy although, on average, we expect a lower star-formation
rate. Studying the radio (1.4GHz) to mid-IR (22micron) flux ratios of the RL
NLS1 in the sample we found that in ~10 objects the star-forming activity could
represent the most important component also at radio frequencies, in addition
(or in alternative) to the relativistic jet. We conclude that both the mid-IR
and the radio emission of RL NLS1 are a mixture of different components,
including the relativistic jet, the dusty torus and an intense star-forming
activity.Comment: Accepted for publication in MNRAS, 11 pages, 7 figures, 2 table
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