588 research outputs found
XMM-Newton observations of the BL Lac MS0205.7+3509: a dense, low-metallicity absorber
The high-frequency-peaked BL Lac, MS0205.7+3509 was observed twice with
XMM-Newton. Both X-ray spectra are synchrotron-dominated, with mean 0.2--10keV
fluxes of 2.80+/-0.01 and 3.34+/-0.02 E-12 erg/cm^2/s. The X-ray spectra are
well fit by a power-law with absorption above the Galactic value, however no
absorption edges are detected, implying a low metallicity absorber (Z_\sun =
0.04(+0.03)(-0.01)) or an absorber with redshift above one (best-fit z=2.1 for
an absorber with solar abundances). In either case the absorbing column density
must be ~9E21 cm^-2. A new optical spectrum is presented, with a MgII
absorption doublet detected at z=0.351, but no other significant features. The
optical spectrum shows little reddening, implying a low dust to gas ratio in
the absorber. MS0205.7+3509 must therefore be viewed through a high column
density, low-metallicity gas cloud, probably at z=0.351 and associated with the
galaxy that has been shown to be within ~2" of the BL Lac.Comment: 5 pages, 4 figures, accepted for publication in A&
Swift detection of all previously undetected blazars in a micro-wave flux-limited sample of WMAP foreground sources
Almost the totality of the bright foreground sources in the WMAP CMB maps are
blazars, a class of sources that show usually also X-ray emission. However, 23
objects in a flux-limited sample of 140 blazars of the WMAP catalog (first
year) were never reported before as X-ray sources. We present here the results
of 41 Swift observations which led to the detection of all these 23 blazars in
the 0.3-10 keV band. We conclude that all micro-wave selected blazars are X-ray
emitters and that the distribution of the micro-wave to X-ray spectral slope
of LBL blazars is very narrow, confirming that the X-ray flux
of most blazars is a very good estimator of their micro-wave emission. The
X-ray spectral shape of all the objects that were observed long enough to allow
spectral analysis is flat and consistent with inverse Compton emission within
the commonly accepted view where the radiation from blazars is emitted in a
Sychrotron-Inverse-Compton scenario. We predict that all blazars and most radio
galaxies above the sensitivity limit of the WMAP and of the Planck CMB missions
are X-ray sources detectable by the present generation of X-ray satellites. An
hypothetical all-sky soft X-ray survey with sensitivity of approximately
erg/s would be crucial to locate and remove over 100,000 blazars
from CMB temperature and polarization maps and therefore accurately clean the
primordial CMB signal from the largest population of extragalactic foreground
contaminants.Comment: 13 pages, 4 figures, 5 tables, A&A in pres
e-Science and biological pathway semantics
<p>Abstract</p> <p>Background</p> <p>The development of e-Science presents a major set of opportunities and challenges for the future progress of biological and life scientific research. Major new tools are required and corresponding demands are placed on the high-throughput data generated and used in these processes. Nowhere is the demand greater than in the semantic integration of these data. Semantic Web tools and technologies afford the chance to achieve this semantic integration. Since pathway knowledge is central to much of the scientific research today it is a good test-bed for semantic integration. Within the context of biological pathways, the BioPAX initiative, part of a broader movement towards the standardization and integration of life science databases, forms a necessary prerequisite for its successful application of e-Science in health care and life science research. This paper examines whether BioPAX, an effort to overcome the barrier of disparate and heterogeneous pathway data sources, addresses the needs of e-Science.</p> <p>Results</p> <p>We demonstrate how BioPAX pathway data can be used to ask and answer some useful biological questions. We find that BioPAX comes close to meeting a broad range of e-Science needs, but certain semantic weaknesses mean that these goals are missed. We make a series of recommendations for re-modeling some aspects of BioPAX to better meet these needs.</p> <p>Conclusion</p> <p>Once these semantic weaknesses are addressed, it will be possible to integrate pathway information in a manner that would be useful in e-Science.</p
The Properties of the Radio-Selected 1Jy Sample of BL Lacertae Objects
We present new optical and near-IR spectroscopy as well as new high dynamic
range, arcsecond-resolution VLA radio maps of BL Lacs from the complete
radio-selected "1 Jansky" (1Jy) sample (RBLs) for which such data were not
previously available. Unlike BL Lacs from the complete X-ray-selected Einstein
Medium Sensitivity Survey (EMSS) sample (XBLs), most RBLs possess weak but
moderately luminous emission lines. And whereas nearly all XBLs have extended
power levels consistent with FR-1s, more than half of the RBLs have extended
radio power levels too luminous to be beamed FR-1 radio galaxies. In fact, we
find evidence for and examples of three distinct mechanisms for creating the BL
Lac phenomenon in the 1Jy sample: beamed FR-1s, beamed FR-2s and possibly a few
gravitationally-lensed quasars. The v/v_max determined for the 1Jy sample is
0.614+/-0.047, which is markedly different from the negative evolution seen in
the EMSS and other XBL samples. A correlation between logarithmic X-ray to
radio flux ratio and v/v_max is observed across the EMSS and 1Jy samples, from
negative evolution in the more extreme XBLs to positive evolution in the more
extreme RBLs. There is evidence that the selection criteria chosen by Stickel
et al. eliminates some BL Lac objects from the 1Jy sample, although how many is
unknown. And several objects currently in the sample have exhibited strong
emission lines in one or more epochs, suggesting they should be reclassified as
FSRQs. However these selection effects cannot account for the observed
discrepancy in XBL and RBL properties. From these observational properties we
conclude that RBLs and XBLs cannot be related by viewing angle alone, and that
RBLs are more closely related to FSRQs.Comment: 29 pages, 47 figures, accepted A
Elevated HbA1c levels and the accumulation of differentiated T cells in CMV+ individuals
Aims/hypothesis Biological ageing of the immune system, or immunosenescence, predicts poor health and increased mortality. A hallmark of immunosenescence is the accumulation of differentiated cytotoxic T cells (CD27âCD45RA+/â; or dCTLs), partially driven by infection with the cytomegalovirus (CMV). Immune impairments reminiscent of immunosenescence are also observed in hyperglycaemia, and in vitro studies have illustrated mechanisms by which elevated glucose can lead to increased dCTLs. This study explored associations between glucose dysregulation and markers of immunosenescence in CMV+ and CMVâ individuals. Methods A cross-sectional sample of participants from an occupational cohort study (nâ=â1,103, mean age 40 years, 88% male) were assessed for HbA1c and fasting glucose levels, diabetes, cardiovascular risk factors (e.g. lipids), numbers of circulating effector memory (EM; CD27âCD45RAâ) and CD45RA re-expressing effector memory (EMRA; CD27âCD45RA+) T cells, and CMV infection status. Self-report and physical examination assessed anthropometric, sociodemographic and lifestyle factors. Results Among CMV+ individuals (nâ=â400), elevated HbA1c was associated with increased numbers of EM (Bâ=â2.75, pâ\u3câ0.01) and EMRA (Bâ=â2.90, pâ\u3câ0.01) T cells, which was robust to adjustment for age, sex, sociodemographic variables and lifestyle factors. Elevated EM T cells were also positively associated with total cholesterol (Bâ=â0.04, pâ\u3câ0.05) after applying similar adjustments. No associations were observed in CMVâ individuals. Conclusions/interpretation The present study identified consistent associations of unfavourable glucose and lipid profiles with accumulation of dCTLs in CMV+ individuals. These results provide evidence that the impact of metabolic risk factors on immunity and health can be co-determined by infectious factors, and provide a novel pathway linking metabolic risk factors with accelerated immunosenescence. Electronic supplementary material The online version of this article (doi:10.1007/s00125-015-3731-4) contains peer-reviewed but unedited supplementary material, which is available to authorised users
C-Reactive Protein in Heart Failure
Backgroundâ
The role of C-reactive protein (CRP) in heart failure is not well studied. We assessed the prognostic value of CRP in patients randomized in Val-HeFT (Valsartan Heart Failure Trial) and studied changes in CRP that were associated with valsartan.
Methods and Resultsâ
Characteristics of patients with baseline CRP levels above and below the median value were compared. Univariable and multivariable Cox proportional hazards regression models were used to examine the relationship of CRP to mortality and morbidity. Interactions were tested to determine whether differences in CRP changes from baseline to 4 and 12 months between groups randomly assigned to valsartan or placebo depended on baseline ACE inhibitor use. Median plasma CRP was 3.23 mg/L (interquartile range 1.42 to 7.56 mg/L), which is higher than in the general population. Patients with CRP above the median had features of more severe heart failure than those with CRP levels below the median. The cumulative likelihood of death and first morbid event increased with increasing quartile of CRP. Relative to the lowest CRP quartile, the risk of mortality (hazard ratio 1.51, 95% CI 1.2 to 1.9) and first morbid event (hazard ratio 1.53, 95% CI 1.28 to 1.84) was increased in the highest CRP quartile in multivariable models. CRP added incremental prognostic information to that provided by brain natriuretic peptide alone. CRP did not change significantly over time in the placebo group; however, after 12 months, valsartan was associated with a decrease in CRP in patients not receiving ACE inhibitors but not in those receiving ACE inhibitors at 12 months.
Conclusionsâ
CRP is increased in heart failure. Higher levels are associated with features of more severe heart failure and are independently associated with mortality and morbidity. The ability of treatments to reduce CRP levels and the prognostic importance of reducing CRP require further study
X-ray Insights into the Nature of Weak Emission-Line Quasars at High Redshift
We present Chandra observations of nine high-redshift quasars (z=2.7-5.9)
discovered by the Sloan Digital Sky Survey with weak or undetectable
high-ionization emission lines in their UV spectra (WLQs). Adding archival
X-ray observations of six additional sources of this class has enabled us to
place the strongest constraints yet on the X-ray properties of this remarkable
class of AGNs. Although our data cannot rule out the possibility that the
emission lines are overwhelmed by a relativistically boosted continuum, as
manifested by BL Lac objects, we find that WLQs are considerably weaker in the
X-ray and radio bands than the majority of BL Lacs found at much lower
redshifts. If WLQs are high-redshift BL Lacs, then it is difficult to explain
the lack of a large parent population of X-ray and radio bright weak-lined
sources at high redshift. We also consider the possibility that WLQs are
quasars with extreme properties, and in particular that the emission lines are
suppressed by high accretion rates. Using joint spectral fitting of the X-ray
spectra of 11 WLQs we find that the mean photon index in the hard X-ray band is
consistent with those observed in typical radio-quiet AGNs with no hint of an
unusually steep hard-X-ray spectrum. This result poses a challenge to the
hypothesis that WLQs have extremely high accretion rates, and we discuss
additional observations required to test this idea.Comment: 13 pages (emulateapj), 7 figures. Accepted for publication in Ap
The Sedentary Multi-Frequency Survey. I. Statistical Identification and Cosmological Properties of HBL BL Lacs
We have assembled a multi-frequency database by cross-correlating the NVSS
catalog of radio sources with the RASSBSC list of soft X-ray sources, obtaining
optical magnitude estimates from the Palomar and UK Schmidt surveys as provided
by the APM and COSMOS on-line services. By exploiting the nearly unique
broad-band properties of High-Energy Peaked (HBL) BL Lacs we have statistically
identified a sample of 218 objects that is expected to include about 85% of BL
Lacs and that is therefore several times larger than all other published
samples of HBLs. Using a subset (155 objects) that is radio flux limited and
statistically well-defined we have derived the \vovm distribution and the
LogN-LogS of extreme HBLs (fx/fr >= 3E-10 erg/cm2/s/Jansky) down to 3.5 mJy. We
find that the LogN-LogS flattens around 20 mJy and that = 0.42 +/- 0.02.
This extends to the radio band earlier results, based on much smaller X-ray
selected samples, about the anomalous cosmological observational properties of
HBL BL Lacs. A comparison with the expected radio LogN-LogS of all BL Lacs
(based on a beaming model) shows that extreme HBLs make up roughly 2% of the BL
Lac population, independently of radio flux. This result, together with the
flatness of the radio logN-logS at low fluxes, is in contrast with the
predictions of a recent model which assumes an anti-correlation between peak
frequency and bolometric luminosity. The extreme fx/fr flux ratios and high
X-ray fluxes of these BL Lacs makes them good candidate TeV sources, some of
the brighter (and closer) ones possibly detectable with the current generation
of Cerenkov telescopes.Comment: 11 pages, LaTeX, 6 ps figures. Accepted for publication in MNRA
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