382 research outputs found
The Blazar Sequence: Validity and Predictions
The "blazar sequence" posits that the most powerful BL Lacertae objects and
flat-spectrum radio quasars should have relatively small synchrotron peak
frequencies, nu_peak, and that the least powerful such objects should have the
highest nu_peak values. This would have strong implications for our
understanding of jet formation and physics and the possible detection of
powerful, moderately high-redshift TeV blazars. I review the validity of the
blazar sequence by using the results of very recent surveys and compare its
detailed predictions against observational data. I find that the blazar
sequence in its simplest form is ruled out. However, powerful flat-spectrum
radio quasars appear not to reach the nu_peak typical of BL Lacs. This could
indeed be related to some sort of sequence, although it cannot be excluded that
it is instead due to a selection effect.Comment: 9 pages, 4 figures, invited talk at the Workshop "The Multi-messenger
approach to high energy gamma-ray sources", Barcelona, Spain, July 4-7, 2006,
to appear in the proceeding
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
Multi-wavelength observations of the obscuring wind in the radio-quiet quasar MR 2251-178
Obscuring winds driven away from active supermassive black holes are rarely
seen due to their transient nature. They have been observed with
multi-wavelength observations in a few Seyfert 1 galaxies and one broad
absorption line radio-quiet quasar so far. An X-ray obscuration event in MR
2251-178 was caught in late 2020, which triggered multi-wavelength (NIR to
X-ray) observations targeting this radio-quiet quasar. In the X-ray band, the
obscurer leads to a flux drop in the soft X-ray band from late 2020 to early
2021. X-ray obscuration events might have a quasi-period of two decades
considering earlier events in 1980 and 1996. In the UV band, a forest of weak
blueshifted absorption features emerged in the blue wing of Ly
in late 2020. Our XMM-Newton, NuSTAR, and HST/COS observations
are obtained simultaneously, hence, the transient X-ray obscuration event is
expected to account for the UV outflow, although they are not necessarily
caused by the same part of the wind. Both blueshifted and redshifted absorption
features were found for He {\sc i} , but no previous NIR spectra
are available for comparison. The X-ray observational features of MR 2251-178
shared similarities with some other type 1 AGNs with obscuring wind. However,
observational features in the UV to NIR bands are distinctly different from
those seen in other AGN with obscuring winds. A general understanding of the
observational variety and the nature of obscuring wind is still lacking.Comment: ApJ accepte
Detailed Structure of the X-ray Jet in 4C 19.44 (=PKS1354+195)
We investigate the variations of the magnetic field, Doppler factor, and
relativistic particle density along the jet of a quasar at z=0.72. We chose 4C
19.44 for this study because of its length and straight morphology. The 18
arcsec length of the jet provides many independent resolution elements in the
Chandra X-ray image. The straightness suggests that geometry factors, although
uncertain, are almost constant along the jet. We assume the X-ray emission is
from inverse Compton scattering of the cosmic microwave background. With the
aid of assumptions about jet alignment, equipartition between magnetic-field
and relativistic-particle energy, and filling factors, we find that the jet is
in bulk relativistic motion with a Doppler factor about 6 at an angle no more
than 10 degrees to the line of sight over deprojected distances about 150--600
kpc from the quasar, and with a magnetic field approximately 10 micro Gauss.Comment: To appear in "Black Holes: from Stars to Galaxies" Proceedings IAU
Symp. No. 238, eds. V. Karas & G. Matt, 2 pages, 1 figure, needs iaus.cl
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
The active galaxy NGC 4151 has a crucial role as one of only two active
galactic nuclei for which black hole mass measurements based on emission line
reverberation mapping can be calibrated against other dynamical methods.
Unfortunately, effective calibration requires an accurate distance to NGC 4151,
which is currently not available. Recently reported distances range from 4 to
29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distance
very uncertain, and the geometry of the galaxy and its nucleus prohibit
accurate measurements using other techniques. Here we report a dust-parallax
distance to NGC 4151 of Mpc. The measurement is
based on an adaptation of a geometric method proposed previously using the
emission line regions of active galaxies. Since this region is too small for
current imaging capabilities, we use instead the ratio of the
physical-to-angular sizes of the more extended hot dust emission as determined
from time-delays and infrared interferometry. This new distance leads to an
approximately 1.4-fold increase in the dynamical black hole mass, implying a
corresponding correction to emission line reverberation masses of black holes
if they are calibrated against the two objects with additional dynamical
masses.Comment: Authors' version of a letter published in Nature (27 November 2014);
8 pages, 5 figures, 1 tabl
The Deep X-Ray Radio Blazar Survey (DXRBS). III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars
Our knowledge of the blazar surface densities and luminosity functions, which
are fundamental parameters, relies still on samples at relatively high flux
limits. As a result, our understanding of this rare class of active galactic
nuclei is mostly based on relatively bright and intrinsically luminous sources.
We present the radio number counts, evolutionary properties, and luminosity
functions of the faintest blazar sample with basically complete (~ 95%)
identifications. Based on the Deep X-ray Radio Blazar Survey (DXRBS), it
includes 129 flat-spectrum radio quasars (FSRQ) and 24 BL Lacs down to a 5 GHz
flux and power ~ 50 mJy and ~ 10^{24} W/Hz, respectively, an order of magnitude
improvement as compared to previously published (radio-selected) blazar
samples. DXRBS FSRQ are seen to evolve strongly, up to redshift ~ 1.5, above
which high-power sources show a decline in their comoving space density. DXRBS
BL Lacs, on the other hand, do not evolve. High-energy (HBL) and low-energy
(LBL) peaked BL Lacs share the same lack of cosmological evolution, which is at
variance with some previous results. The observed luminosity functions are in
good agreement with the predictions of unified schemes, with FSRQ getting close
to their expected minimum power. Despite the fact that the large majority of
our blazars are FSRQ, BL Lacs are intrinsically ~ 50 times more numerous.
Finally, the relative numbers of HBL and LBL in the radio and X-ray bands are
different from those predicted by the so-called "blazar sequence" and support a
scenario in which HBL represent a small minority (~ 10%) of all BL Lacs.Comment: 19 pages, 14 figures (1 color), accepted for publication in the
Astrophysical Journa
The Spitzer High Redshift Radio Galaxy Survey
We present results from a comprehensive imaging survey of 70 radio galaxies
at redshifts 1<z<5.2 using all three cameras onboard the Spitzer Space
Telescope. The resulting spectral energy distributions unambiguously show a
stellar population in 46 sources and hot dust emission associated with the
active nucleus in 59. Using a new restframe S_3um/S_1.6um versus S_um/S_3um
criterion, we identify 42 sources where the restframe 1.6um emission from the
stellar population can be measured. For these radio galaxies, the median
stellar mass is high, 2x10^11 M_sun, and remarkably constant within the range
13, there is tentative evidence for a factor of two decrease in
stellar mass. This suggests that radio galaxies have assembled the bulk of
their stellar mass by z~3, but confirmation by more detailed decomposition of
stellar and AGN emission is needed.
The restframe 500 MHz radio luminosities are only marginally correlated with
stellar mass but are strongly correlated with the restframe 5um hot dust
luminosity. This suggests that the radio galaxies have a large range of
Eddington ratios. We also present new Very Large Array 4.86 and 8.46 GHz
imaging of 14 radio galaxies and find that radio core dominance --- an
indicator of jet orientation --- is strongly correlated with hot dust
luminosity. While all of our targets were selected as narrow-lined, type 2
AGNs, this result can be understood in the context of orientation-dependent
models if there is a continuous distribution of orientations from obscured type
2 to unobscured type 1 AGNs rather than a clear dichotomy. Finally, four radio
galaxies have nearby (<6") companions whose mid-IR colors are suggestive of
their being AGNs. This may indicate an association between radio galaxy
activity and major mergers.Comment: 31 pages, 125 figures. Accepted for publication in the Astrophysical
Journa
Simultaneous Planck, Swift, and Fermi observations of X-ray and gamma-ray selected blazars
We present simultaneous Planck, Swift, Fermi, and ground-based data for 105
blazars belonging to three samples with flux limits in the soft X-ray, hard
X-ray, and gamma-ray bands. Our unique data set has allowed us to demonstrate
that the selection method strongly influences the results, producing biases
that cannot be ignored. Almost all the BL Lac objects have been detected by
Fermi-LAT, whereas ~40% of the flat-spectrum radio quasars (FSRQs) in the
radio, soft X-ray, and hard X-ray selected samples are still below the
gamma-ray detection limit even after integrating 27 months of Fermi-LAT data.
The radio to sub-mm spectral slope of blazars is quite flat up to ~70GHz, above
which it steepens to ~-0.65. BL Lacs have significantly flatter spectra
than FSRQs at higher frequencies. The distribution of the rest-frame
synchrotron peak frequency (\nupS) in the SED of FSRQs is the same in all the
blazar samples with =10^13.1 Hz, while the mean inverse-Compton peak
frequency, , ranges from 10^21 to 10^22 Hz. The distributions of \nupS
and of \nupIC of BL Lacs are much broader and are shifted to higher energies
than those of FSRQs and strongly depend on the selection method. The Compton
dominance of blazars ranges from ~0.2 to ~100, with only FSRQs reaching values
>3. Its distribution is broad and depends strongly on the selection method,
with gamma-ray selected blazars peaking at ~7 or more, and radio-selected
blazars at values ~1, thus implying that the assumption that the blazar power
is dominated by high-energy emission is a selection effect. Simple SSC models
cannot explain the SEDs of most of the gamma-ray detected blazars in all
samples. The SED of the blazars that were not detected by Fermi-LAT may instead
be consistent with SSC emission. Our data challenge the correlation between
bolometric luminosity and \nupS predicted by the blazar sequence.Comment: Version accepted by A&A. Joint Planck, Swift, and Fermi
collaborations pape
Heparan sulfate and heparin interactions with proteins.
Heparan sulfate (HS) polysaccharides are ubiquitous components of the cell surface and extracellular matrix of all multicellular animals, whereas heparin is present within mast cells and can be viewed as a more sulfated, tissuespecific, HS variant. HS and heparin regulate biological processes through interactions with a large repertoire of proteins. Owing to these interactions
and diverse effects observed during in vitro, ex vivo and in vivo experiments, manifold biological/pharmacological activities have been attributed to them. The properties that have been thought to bestow protein binding and
biological activity upon HS and heparin vary from high levels of sequence specificity to a dependence on charge. In contrast to these opposing opinions, we will argue that the evidence supports both a level of redundancy and a
degree of selectivity in the structure–activity relationship. The relationship between this apparent redundancy, the multi-dentate nature of heparin and HS polysaccharide chains, their involvement in protein networks and the multiple binding sites on proteins, each possessing different properties, will also be considered. Finally, the role of cations in modulating HS/heparin activity will be reviewed and some of the implications for structure–activity relationships and regulation will be discussed
The clinical and molecular spectrum of galactosemia in patients from the Cape Town region of South Africa
BACKGROUND: The objective of this study was to document the clinical, laboratory and genetic features of galactosemia in patients from the Cape Town metropolitan region. METHODS: Diagnoses were based on thin layer chromatography for galactosuria/galactosemia and assays of erythrocyte galactose-1-phosphate uridyltransferase (GALT) and galactokinase activities. Patients were screened for the common S135L and Q188R transferase gene mutations, using PCR-based assays. Screening for the S135L mutation in black newborns was used to estimate the carrier rate for galactosemia in black South Africans. RESULTS: A positive diagnosis of galactosemia was made in 17 patients between the years 1980 to 2001. All had very low or absent galactose-1-phosphate uridyltransferase (GALT) activity, and normal galactokinase levels. The mean age at diagnosis was 5.1 months (range 4 days to 6.5 months). A review of 9 patients showed that hepatomegaly (9/9), and splenomegaly, failure to thrive, developmental delay, bilateral cataracts (6/9) were the most frequent features at diagnosis. Six had conjugated hyperbilirubinemia. Four experienced invasive E. coli infection before diagnosis. Ten patients were submitted to DNA analysis. All 4 black patients and 2 of mixed extraction were homozygous for the S135L allele, while all 3 white patients were homozygous for the Q188R allele. The remaining patient of mixed extraction was heterozygous for the Q188R allele. The estimated carrier frequency of the S135L mutation in 725 healthy black newborns was 1/60. CONCLUSIONS: In the absence of newborn screening the delay in diagnosis is most often unacceptably long. Also, carrier frequency data predict a galactosemia incidence of approximately 1/14 400 for black newborns in the Cape Metropole, which is much higher than the current detection rate. It is thus likely that many patients go undetected
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