79 research outputs found
VLA Observations of a New Population of Blazars
We present the first deep VLA radio images of flat-spectrum radio quasars
(FSRQ) with multiwavelength emission properties similar to those of BL Lacs
with synchrotron X-rays. Our observations of twenty-five of these sources show
that their radio morphologies are similar to those of other radio quasars.
However, their range of extended powers is more similar to that of BL Lacertae
objects (BL Lacs) and extends down to the low values typical of FR I radio
galaxies. Five out of our nine lobe-dominated sources have extended radio
powers in the range typical of both FR I and FR II radio galaxies, but their
extended radio structure is clearly FR II-like. Therefore, we have not yet
found a large population of radio quasars hosted by FR Is. Two thirds of our
sources have a core-dominated radio morpholgy and thus X-rays likely dominated
by the jet. We find that their ratios of radio core to total X-ray luminosity
are low and in the regime indicative of synchrotron X-rays. This result shows
that also blazars with strong emission lines can produce jets of high-energy
synchrotron emission and undermines at least in part the ``blazar sequence''
scenario which advocates that particle Compton cooling by an external radiation
field governs the frequency of the synchrotron emission peak.Comment: 26 pages, 33 figures. Accepted for publication in Ap
Poverty and Disability: A critical review of the literature in low and middle-income countries
While it is widely assumed that disability, poverty and health are closely linked, this is the
first critical review on the subject that explicitly asks: ‘What is the current evidence base
for the link between poverty, disability and health in low- and middle-income countries?
The methods used have been adapted from the EPPI Centre (EPPI-Centre, 2007) and the
work of Greenhalgh (Greenhalgh, Robert, Macfarlane, Bate, Kyriakidou, & Peacock, 2005)
A total of 964 papers were identified and, of these, 293 were selected for further review
based on appropriateness of fit. An initial review of the 293 papers, paying particular
attention to those papers that presented an evidence base, found only 27 papers (9.2% of
total papers reviewed) met the established inclusion criteria for a critical review. Widening
these inclusion criteria did not produce significantly more evidence based papers for
review. Thus, the most significant finding from this study is the current lack of strong
evidence on the links between disability, poverty and health in LMICs upon which to build
global policy and programming. Within the group of papers available for review, we
identify a small but growing evidence base that indicates that there are substantial links
between disability, poverty and health; however emerging research indicates that these
links are more complex and nuanced than is currently assumed. We conclude with a call
for more attention to building an evidence base on the interactions between disability,
poverty and health. The absence of a robust evidence base that explicitly links these
issues, in conjunction with the lack of appropriate benchmarks and indicators to measure
disability rights commitments (including poverty reduction), will otherwise result in a
“democratic deficit”
The chaotic behavior of the black hole system GRS 1915+105
A modified non-linear time series analysis technique, which computes the
correlation dimension , is used to analyze the X-ray light curves of the
black hole system GRS 1915+105 in all twelve temporal classes. For four of
these temporal classes saturates to which indicates that
the underlying dynamical mechanism is a low dimensional chaotic system. Of the
other eight classes, three show stochastic behavior while five show deviation
from randomness. The light curves for four classes which depict chaotic
behavior have the smallest ratio of the expected Poisson noise to the
variability () while those for the three classes which depict
stochastic behavior is the highest (). This suggests that the temporal
behavior of the black hole system is governed by a low dimensional chaotic
system, whose nature is detectable only when the Poisson fluctuations are much
smaller than the variability.Comment: Accepted for publication in Astrophysical Journa
The Nuclear Reddening Curve for Active Galactic Nuclei and the Shape of the Infra-Red to X-Ray Spectral Energy Distribution
We present extinction curves derived from the broad emission lines and
continua of large samples of both radio-loud and radio-quiet AGNs. The curves
are significantly flatter in the UV than are curves for the local ISM. The
reddening curves for the radio-quiet LBQS quasars are slightly steeper than
those of the radio-loud quasars in the UV, probably because of additional
reddening by dust further out in the host galaxies of the former. The UV
extinction curves for the radio-loud AGNs are very flat. This is explicable
with slight modifications to standard MRN dust models: there is a relative lack
of small grains in the nuclear dust. Our continuum and broad-emission line
reddening curves agree in both shape and amplitude, confirming that the
continuum shape is indeed profoundly affected by reddening for all but the
bluest AGNs. With correction by our generic extinction curve, all of the
radio-loud AGNs have continuous optical-UV spectra consistent with a single
shape. We show that radio-quiet AGNs have very similar intrinsic UV to optical
shape over orders of magnitude in luminosity. We also argue that radio-loud and
radio-quiet AGNs probably share the same underlying continuum shape and that
most of the systematic differences between their observed continuum shapes are
due to higher nuclear reddening in radio-selected AGNs, and additional
reddening from dust further out in the host galaxies in radio-quiet AGNs. Our
conclusions have important implications for the modelling of quasar continua
and the analysis of quasar demographics.Comment: 41 pages, including 6 figures and 3 tables. To appear in ApJ vol.
614, October 20 issue. Some slight wording changes. Some additional
references added. Small changes in the model fit in section 6.2, to the
analytical fit in the Appendix, and to the tabulated reddening curve in the
Appendi
Broadening of the Iron emission line in MCG-6-30-15 by Comptonization
We show that the Iron K emission line from MCG-6-30-15 could be broadened due
to Comptonization by a surrounding highly ionized cloud with radius cms. We calculate the temperature of the cloud to be \sim0.21\kev,
provided a reasonable estimate of the UV flux is made. The X-ray/-ray
emission observed from the source is compatible with this model. Such a cloud
should be highly ionized and strong absorption edges are not expected from the
source (Fabian et al 1995).
For a \onlyten{6}\msol black hole the size of the could corresponds to
about 300 Schwarzschild radius. The intrinsic line could then be emitted far
from the black hole and gravitational red-shift and Doppler effects would be
negligible. If the black hole mass is much larger than \onlyten{6}\msol,
gravitational/Doppler red-shifts would also contribute significantly to the
broadening.
We argue that the broad red wing observed in the source does not by itself
imply emission from regions close () to the black hole. However,
Comptonization cannot produce a double peak. The presence of such a feature is
a clear sign of inner disk emission influenced by gravitational and Doppler
effects, perhaps broadened by the Comptonization. We note that simultaneous
broad band (2-100 keV) study of this source can also reveal (or rule out) the
presence of such a Comptonizing cloud.Comment: 2 figures. uses aasms4.sty, accepted by ApJ, email:
[email protected]
A search for linear polarization in the active galactic nucleus 3C 84 at 239 and 348 GHz
We report a search for linear polarization in the active galactic nucleus
(AGN) 3C 84 (NGC 1275) at observed frequencies of 239 GHz and 348 GHz,
corresponding to rest-frame frequencies of 243 GHz and 354 GHz. We collected
polarization data with the IRAM Plateau de Bure Interferometer via Earth
rotation polarimetry. We do not detect linear polarization. Our analysis finds
3-sigma upper limits on the degree of polarization of 0.5% and 1.9% at 239 GHz
and 348 GHz, respectively. We regard the influence of Faraday conversion as
marginal, leading to expected circular polarizations <0.3%. Assuming
depolarization by a local Faraday screen, we constrain the rotation measure, as
well as the fluctuations therein, to be 10^6 rad/m^2. From this we estimate
line-of-sight magnetic field strengths of >100 microG. Given the physical
dimensions of 3C 84 and its observed structure, the Faraday screen appears to
show prominent small-scale structure, with \DeltaRM > 10^6 rad/m^2 on projected
spatial scales <1 pc.Comment: 7 pages, 4 figures. Accepted by MNRA
IMAGES II. A surprisingly low fraction of undisturbed rotating spiral disks at z~0.6: The morpho-kinematical relation 6 Gyrs ago
We present a first combined analysis of the morphological and dynamical
properties for the Intermediate MAss Galaxy Evolution Sequence (IMAGES) sample.
It is a representative sample of 52 z~0.6 galaxies with Mstell from 1.5 to 15
10^10Msun and possessing 3D resolved kinematics and HST deep imaging in at
least two broad band filters. We aim at evaluate robustly the evolution of
rotating spirals since z~0.6, as well as to test the different schemes for
classifying galaxies morphologically. We used all the information provided by
multi-band images, color maps and 2 dimensional light fitting to assign to each
object a morphological class. We divided our sample between spiral disks,
peculiar objects, compact objects and mergers. Using our morphological
classification scheme, 4/5 of identified spirals are rotating disks and more
than 4/5 of identified peculiar galaxies show complex kinematics, while
automatic classification methods such as Concentration-Asymmetry and GINI-M20
severely overestimate the fraction of relaxed disk galaxies. Using this
methodology, we find that the fraction of rotating spirals has increased by a
factor ~ 2 during the last 6 Gyrs, a much higher fraction that found previously
based on morphologies alone. These rotating spiral disks are forming stars very
rapidly, doubling their stellar masses over the last 6 Gyrs, while most of
their stars have been formed few Gyrs earlier, which reveals the presence of a
large gas supply. Because they are likely the progenitors of local spirals, we
can conjecture how their properties are evolving. Their disks show some
evidence for an inside-out growth and the gas supply/accretion is not made
randomly as the disk need to be stable in order to match the local disk
properties.Comment: Typos corrected, reference adde
Stochastic evolution of cosmological parameters in the early universe
We develop a stochastic formulation of cosmology in the early universe, after
considering the scatter in the redshift-apparent magnitude diagram in the early
epochs as an observational evidence for the non-deterministic evolution of
early universe. We consider the stochastic evolution of density parameter in
the early universe after the inflationary phase qualitatively, under the
assumption of fluctuating factor in the equation of state, in the
Fokker-Planck formalism. Since the scale factor for the universe depends on the
energy density, from the coupled Friedmann equations we calculated the two
variable probability distribution function assuming a flat space geometry.Comment: 10 page
Broad-band X-ray emission and the reality of the broad iron line from the neutron star–white dwarf X-ray binary 4U 1820−30
Broad relativistic iron lines from neutron star X-ray binaries are important probes of the inner accretion disc. The X-ray reflection features can be weakened due to strong magnetic fields or very low iron abundances such as is possible in X-ray binaries with low mass, first generation stars as companions. Here, we investigate the reality of the broad iron line detected earlier from the neutron-star low-mass X-ray binary 4U 1820−30 with a degenerate helium dwarf companion. We perform a comprehensive, systematic broad-band spectral study of the atoll source using Suzaku and simultaneous NuSTAR and Swift observations. We have used different continuum models involving accretion disc emission, thermal blackbody and thermal Comptonization of either disc or blackbody photons. The Suzaku data show positive and negative residuals in the region of Fe K band. These features are well described by two absorption edges at 7.67 ± 0.14 keV and 6.93 ± 0.07 keV or partial covering photoionized absorption or by blurred reflection. Though, the simultaneous Swift and NuSTAR data do not clearly reveal the emission or absorption features, the data are consistent with the presence of either absorption or emission features. Thus, the absorption based models provide an alternative to the broad iron line or reflection model. The absorption features may arise in winds from the inner accretion disc. The broad-band spectra appear to disfavour continuum models in which the blackbody emission from the neutron-star surface provides the seed photons for thermal Comptonization. Our results suggest emission from a thin accretion disc (kT_(disc) ∼ 1 keV), Comptonization of disc photons in a boundary layer most likely covering a large fraction of the neutron-star surface and innermost parts of the accretion disc, and blackbody emission (kT_(bb) ∼ 2 keV) from the polar regions
Images IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies since z=0.8
Intermediate mass galaxies (logM(Msun)>10) at z~0.6 are the likeliest
progenitors of the present-day numerous population of spirals. There is growing
evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and
likely have formed a significant fraction of their stellar mass, often showing
perturbed morphologies and kinematics. We have gathered a representative sample
of 88 such galaxies and have provided robust estimates of their gas phase
metallicity. For doing so, we have used moderate spectral resolution
spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases
coming from interstellar absorption lines and extinction to establish robust
values of R23=([OII]3727 + [OIII]4959,5007)/Hbeta. We definitively confirm that
the predominant population of z~0.6 starbursts and luminous IR galaxies (LIRGs)
are on average, two times less metal rich than the local galaxies at a given
stellar mass. We do find that the metal abundance of the gaseous phase of
galaxies is evolving linearly with time, from z=1 to z=0 and after comparing
with other studies, from z=3 to z=0. Combining our results with the reported
evolution of the Tully Fisher relation, we do find that such an evolution
requires that ~30% of the stellar mass of local galaxies have been formed
through an external supply of gas, thus excluding the close box model. Distant
starbursts & LIRGs have properties (metal abundance, star formation efficiency
& morphologies) similar to those of local LIRGs. Their underlying physics is
likely dominated by gas infall probably through merging or interactions. Our
study further supports the rapid evolution of z~0.4-1 galaxies. Gas exchanges
between galaxies is likely the main cause of this evolution.Comment: 21 pages, 12 figures, A&A, In pres
- …