438 research outputs found
Fermi-LAT and Suzaku Observations of the Radio Galaxy Centaurus B
Centaurus B is a nearby radio galaxy positioned in the Southern hemisphere
close to the Galactic plane. Here we present a detailed analysis of about 43
months of accumulated Fermi-LAT data of the gamma-ray counterpart of the source
initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku
X-ray data. We confirm its detection at GeV photon energies, and analyze the
extension and variability of the gamma-ray source in the LAT dataset, in which
it appears as a steady gamma-ray emitter. The X-ray core of Centaurus B is
detected as a bright source of a continuum radiation. We do not detect however
any diffuse X-ray emission from the known radio lobes, with the provided upper
limit only marginally consistent with the previously claimed ASCA flux. Two
scenarios that connect the X-ray and gamma-ray properties are considered. In
the first one, we assume that the diffuse non-thermal X-ray emission component
is not significantly below the derived Suzaku upper limit. In this case,
modeling the inverse-Compton emission shows that the observed gamma-ray flux of
the source may in principle be produced within the lobes. This association
would imply that efficient in-situ acceleration of the radiating electrons is
occurring and that the lobes are dominated by the pressure from the
relativistic particles. In the second scenario, with the diffuse X-ray emission
well below the Suzaku upper limits, the lobes in the system are instead
dominated by the magnetic pressure. In this case, the observed gamma-ray flux
is not likely to be produced within the lobes, but instead within the nuclear
parts of the jet. By means of synchrotron self-Compton modeling we show that
this possibility could be consistent with the broad-band data collected for the
unresolved core of Centaurus B, including the newly derived Suzaku spectrum.Comment: Accepted for publication in A&A. 11 page
Fermi-LAT Observation of Supernova Remnant S147
We present an analysis of gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region
around SNR S147 (G180.0-1.7). A spatially extended gamma-ray source detected in
an energy range of 0.2--10 GeV is found to coincide with SNR S147. We confirm
its spatial extension at >5sigma confidence level. The gamma-ray flux is (3.8
\pm 0.6) x 10^{-8} photons cm^{-2} s^{-1}, corresponding to a luminosity of 1.3
x 10^{34} (d/1.3 kpc)^2 erg s^{-1} in this energy range. The gamma-ray emission
exhibits a possible spatial correlation with prominent Halpha filaments of
S147. There is no indication that the gamma-ray emission comes from the
associated pulsar PSR J0538+2817. The gamma-ray spectrum integrated over the
remnant is likely dominated by the decay of neutral pi mesons produced through
the proton--proton collisions in the filaments. Reacceleration of pre-existing
CRs and subsequent adiabatic compression in the filaments is sufficient to
provide the required energy density of high-energy protons.Comment: 12 pages, accepted for publication in Ap
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of
SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a
significance of 38 sigma is found to coincide with SNR W49B. The energy
spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The
luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy
range. There is no indication that the gamma-ray emission comes from a pulsar.
Assuming that the SNR shell is the site of gamma-ray production, the observed
spectrum can be explained either by the decay of neutral pi mesons produced
through the proton-proton collisions or by electron bremsstrahlung. The
calculated energy density of relativistic particles responsible for the LAT
flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either
gamma-ray production mechanism.Comment: 9 pages, 10 figure
Fermi-LAT Discovery of Extended Gamma-ray Emission in the Direction of Supernova Remnant W51C
The discovery of bright gamma-ray emission coincident with supernova remnant
(SNR) W51C is reported using the Large Area Telescope (LAT) on board the Fermi
Gamma-ray Space Telescope. W51C is a middle-aged remnant (~10^4 yr) with
intense radio synchrotron emission in its shell and known to be interacting
with a molecular cloud. The gamma-ray emission is spatially extended, broadly
consistent with the radio and X-ray extent of SNR W51C. The energy spectrum in
the 0.2-50 GeV band exhibits steepening toward high energies. The luminosity is
greater than 1x10^{36} erg/s given the distance constraint of D>5.5 kpc, which
makes this object one of the most luminous gamma-ray sources in our Galaxy. The
observed gamma-rays can be explained reasonably by a combination of efficient
acceleration of nuclear cosmic rays at supernova shocks and shock-cloud
interactions. The decay of neutral pi-mesons produced in hadronic collisions
provides a plausible explanation for the gamma-ray emission. The product of the
average gas density and the total energy content of the accelerated protons
amounts to 5x10^{51}(D/6kpc)^2 erg/cm^3. Electron density constraints from the
radio and X-ray bands render it difficult to explain the LAT signal as due to
inverse Compton scattering. The Fermi LAT source coincident with SNR W51C sheds
new light on the origin of Galactic cosmic rays.Comment: 17 pages, 4 figures, 1 table. Accepted for ApJ Letters. Contact
authors: Y. Uchiyama, S. Funk., H. Tajima, T. Tanak
Beclin-1 Expression is a Predictor of Clinical Outcome in Patients with Esophageal Squamous Cell Carcinoma and Correlated to Hypoxia-Inducible Factor (HIF)-1α Expression
In the present study, we examined the relationship between Beclin-1 expression and HIF-1α expression in esophageal squamous cell carcinoma(ESCC). There was a loss of Beclin-1 protein expression in 33% of ESCCs. Beclin-1 expression significantly correlated with depth of invasion, lymph node metastasis and clinical stage. Among the 54 patients, The survival rate of the Beclin-1-positive group was better than that of the Beclin-1-negative group. Twenty-five of the 54 (46%) tumor specimens showed high levels of HIF-1α immunoreactivity. Beclin-1 expression was associated with HIF-1α expression. The survival rate of patients with Beclin-1-positive and HIF-1α-low tumors was significantly higher than that of the other groups. These results suggest that Beclin-1 and HIF-1α expression are important determinants of survival in ESCCs
Effect of the Glycemic Index of Carbohydrates on Acne vulgaris
Acne vulgaris may be improved by dietary factors that increase insulin sensitivity. We hypothesized that a low-glycemic index diet would improve facial acne severity and insulin sensitivity. Fifty-eight adolescent males (mean age ± standard deviation 16.5 ± 1.0 y and body mass index 23.1 ± 3.5 kg/m2) were alternately allocated to high or low glycemic index diets. Severity of inflammatory lesions on the face, insulin sensitivity (homeostasis modeling assessment of insulin resistance), androgens and insulin-like growth factor-1 and its binding proteins were assessed at baseline and at eight weeks, a period corresponding to the school term. Forty-three subjects (n = 23 low glycemic index and n = 20 high glycemic index) completed the study. Diets differed significantly in glycemic index (mean ± standard error of the mean, low glycemic index 51 ± 1 vs. high glycemic index 61 ± 2, p = 0.0002), but not in macronutrient distribution or fiber content. Facial acne improved on both diets (low glycemic index −26 ± 6%, p = 0.0004 and high glycemic index −16 ± 7%, p = 0.01), but differences between diets did not reach significance. Change in insulin sensitivity was not different between diets (low glycemic index 0.2 ± 0.1 and high glycemic index 0.1 ± 0.1, p = 0.60) and did not correlate with change in acne severity (Pearson correlation r = −0.196, p = 0.244). Longer time frames, greater reductions in glycemic load or/and weight loss may be necessary to detect improvements in acne among adolescent boys
Protective Unfolded Protein Response in Human Pancreatic Beta Cells Transplanted into Mice
Background: There is great interest about the possible contribution of ER stress to the apoptosis of pancreatic beta cells in the diabetic state and with islet transplantation. Methods and Findings: Expression of genes involved in ER stress were examined in beta cell enriched tissue obtained with laser capture microdissection (LCM) from frozen sections of pancreases obtained from non-diabetic subjects at surgery and from human islets transplanted into ICR-SCID mice for 4 wk. Because mice have higher glucose levels than humans, the transplanted beta cells were exposed to mild hyperglycemia and the abnormal environment of the transplant site. RNA was extracted from the LCM specimens, amplified and then subjected to microarray analysis. The transplanted beta cells showed an unfolded protein response (UPR). There was activation of many genes of the IRE-1 pathway that provide protection against the deleterious effects of ER stress, increased expression of ER chaperones and ERAD (ER-associated protein degradation) proteins. The other two arms of ER stress, PERK and ATF-6, had many down regulated genes. Downregulation of EIF2A could protect by inhibiting protein synthesis. Two genes known to contribute to apoptosis, CHOP and JNK, were downregulated. Conclusions: Human beta cells in a transplant site had UPR changes in gene expression that protect against the proapoptotic effects of unfolded proteins
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