414 research outputs found
X-Ray and Ray Astronomy At The Turning Point
Since 1962, approximately 40 point X-ray sources have been isolated, only about six of which have been identified with known radio or optical objects or have been studied over the 1 - 300 keV energy range. Data on the X-ray fluxes, positions, sizes and spectra of these sources have provided new information of considerable astrophysical significance and indicate that the exploratory stage of X-ray astronomy is now over. At higher energies, confirmation of a diffuse flux to 6 MeV and the successful detection of 100 MeV -y-rays from the galaxy indicate the necessity of further exploratory experiments. Satellite borne instruments on a larger scale than previously implemented will be needed to take advantage of the unique opportunity now available for advancing high-energy astrophysics
The Spectrum of Crab Nebula X-Rays to 120 Kev
Counting rate and pulse height distribution spectral data of Crab Nebula telemetered from balloon detector
IL-10 is necessary and sufficient for autoimmune diabetes in conjunction with NOD MHC homozygosity.
Contrary to expectations based on in vitro experiments, we previously found that pancreatic IL-10 did not inhibit autoimmune diabetes but accelerated it in an MHC-dependent manner. Therefore, the ability of IL-10 to overcome the absence of all non-MHC diabetes susceptibility (Idd) alleles was studied in transgenic mice expressing pancreatic IL-10 backcrossed to B10.H2g7 congenic mice, which have no Idd alleles other than NOD MHC (H2g7). IL-10 transgenic backcross 1 (BC1) mice with H2g7/g7 haplotype developed clear-cut insulitis and diabetes, but neither transgenic mice with the H2g/b haplotype nor nontransgenic BC1 mice did so. Further implicating IL-10 in autoimmune diabetes, anti-IL-10 antibody treatment inhibited the development of insulitis in NOD mice. These results suggest that IL-10 may be necessary and sufficient for producing autoimmune diabetes in conjunction with NOD MHC homozygosity and that some Idd genes may be related to the regulation of IL-10
A Chandra study of the large-scale shock and cool filaments in Hydra A: Evidence for substantial gas dredge-up by the central outburst
We present the results of a Chandra study of the Hydra A galaxy cluster,
where a powerful AGN outburst created a large-scale cocoon shock. We
investigated possible azimuthal variations in shock strength and shape, finding
indications for a weak shock with a Mach number in the range ~1.2-1.3. We
measured the temperature change across the shock front. However, the detection
of a temperature rise in the regions immediately inside of the front is
complicated by the underlying temperature profile of the cluster atmosphere. We
measured the global temperature profile of the cluster up to 700 kpc, which
represents the farthest measurement obtained with Chandra for this cluster. A
"plateau" in the temperature profile in the range ~70-150 kpc indicates the
presence of cool gas, which is likely the result of uplift of material by the
AGN outburst. After masking the cool filaments visible in the hardness ratio
map, the plateau disappears and the temperature profile recovers a typical
shape with a peak around 190 kpc, just inside the shock front. However, it is
unlikely that such a temperature feature is produced by the shock as it is
consistent with the general shape of the temperature profiles observed for
relaxed galaxy clusters. We studied the spectral properties of the cool
filaments finding evidence that ~10^11 M_sun of low-entropy material has been
dredged up by the rising lobes from the central 30 kpc to the observed current
position of 75-150 kpc. The energy required to lift the cool gas is >~2.2 x
10^60 erg, which is comparable to the work required to inflate the cavities and
is ~25% of the total energy of the large-scale shock. Our results show that the
AGN feedback in Hydra A is acting not only by directly heating the gas, but
also by removing a substantial amount of potential fuel for the SMBH.Comment: 11 pages, 9 figures, accepted for publication in ApJ (version with
full resolution figures available at
http://www.bo.astro.it/~myriam/files/papers/gitti-hydra.pdf
Editor\u27s Corner - New Assistant Editors
It is a special pleasure to introduce two new assistant editors in the physical sciences. Chemistry and physics articles have not been abundant in recent issues and both editors are particularly interested in locating articles of practical value to classroom teachers. As each of the new editors states in his editorial, many readers have excellent ideas for classroom activities. Some of these activities may not be totally new but have a new approach which will prove helpful to other teachers. The entire editorial staff is eager to aid you in preparing articles for publication. Contact one of the editors to help you share your ideas with the profession
Cavities and shocks in the galaxy group HCG 62 as revealed by Chandra, XMM and GMRT data
We report on the results of an analysis of Chandra, XMM-Newton and new GMRT
data of the X-ray bright compact group of galaxies HCG 62, which is one of the
few groups known to possess clear, small X-ray cavities in the inner regions.
This is part of an ongoing X-ray/low-frequency radio study of 18 groups,
initially chosen for the availability of good-quality X-ray data and evidence
for AGN/hot gas interaction. At higher frequency (1.4 GHz), the HCG 62 cavity
system shows minimal if any radio emission, but the new GMRT observations at
235 MHz and 610 MHz clearly detect extended low-frequency emission from radio
lobes corresponding to the cavities. By means of the synergy of X-ray and
low-frequency radio observations, we compare and discuss the morphology,
luminosity and pressure of the gas and of the radio source. We find that the
radio source is radiatively inefficient, with a ratio of radio luminosity to
mechanical cavity power of , and that the radio pressure of the
lobes is about one order of magnitude lower than the X-ray pressure of the
surrounding thermal gas. Thanks to the high spatial resolution of the Chandra
surface brightness and temperature profiles, we also identify a shock front
located at 36 kpc to the south-west of the group center, close to the southern
radio lobe, with a Mach number and a total power which is about one
order of magnitude higher than the cavity power. Such a shock may have heated
the gas in the southern region, as indicated by the temperature map. The shock
may also explain the arc-like region of enriched gas seen in the iron abundance
map, as this may be produced by a non-Maxwellian electron distribution near its
front.Comment: 14 pages, 8 figures, accepted for publication in ApJ. Revised version
including minor comments and expanded discussion (version with full
resolution figures available at
http://hea-www.harvard.edu/~mgitti/hcg62-gitti.pdf
Isotropic AGN Heating with Small Radio Quiet Bubbles in the NGC 5044 Group
(abridged) A Chandra observation of the X-ray bright group NGC 5044 shows
that the X-ray emitting gas has been strongly perturbed by recent outbursts
from the central AGN and also by motion of the central dominant galaxy relative
to the group gas. The NGC 5044 group hosts many small radio quiet cavities with
a nearly isotropic distribution, cool filaments, a semi-circular cold front and
a two-armed spiral shaped feature of cool gas. A GMRT observation of NGC 5044
at 610 MHz shows the presence of extended radio emission with a "torus-shaped"
morphology. The largest X-ray filament appears to thread the radio torus,
suggesting that the lower entropy gas within the filament is material being
uplifted from the center of the group. The radio emission at 235 MHz is much
more extended than the emission at 610 MHz, with little overlap between the two
frequencies. One component of the 235 MHz emission passes through the largest
X-ray cavity and is then deflected just behind the cold front. A second
detached radio lobe is also detected at 235 MHz beyond the cold front. All of
the smaller X-ray cavities in the center of NGC 5044 are undetected in the GMRT
observations. Since the smaller bubbles are probably no longer momentum driven
by the central AGN, their motion will be affected by the group "weather" as
they buoyantly rise outward. Hence, most of the enthalpy within the smaller
bubbles will likely be deposited near the group center and isotropized by the
group weather. The total mechanical power of the smaller radio quiet cavities
is erg s which is sufficient to suppress about
one-half of the total radiative cooling within the central 10 kpc. This is
consistent with the presence of H emission within this region which
shows that at least some of the gas is able to cool
A deep Chandra observation of the poor cluster AWM 4 - I. Properties of the central radio galaxy and its effects on the intracluster medium
Using observations from the Chandra X-ray Observatory and Giant Metrewave
Radio Telescope, we examine the interaction between the intracluster medium and
central radio source in the poor cluster AWM 4. In the Chandra observation a
small cool core or galactic corona is resolved coincident with the radio core.
This corona is capable of fuelling the active nucleus, but must be
inefficiently heated by jet interactions or conduction, possibly precluding a
feedback relationship between the radio source and cluster. A lack of clearly
detected X-ray cavities suggests that the radio lobes are only partially filled
by relativistic plasma. We estimate a filling factor of phi=0.21 (3 sigma upper
limit phi<0.42) for the better constrained east lobe. We consider the particle
population in the jets and lobes, and find that the standard equipartition
assumptions predict pressures and ages which agree poorly with X-ray estimates.
Including an electron population extending to low Lorentz factors either
reduces (gamma_min=100) or removes (gamma_min=10) the pressure imbalance
between the lobes and their environment. Pressure balance can also be achieved
by entrainment of thermal gas, probably in the first few kiloparsecs of the
radio jets. We estimate the mechanical power output of the radio galaxy, and
find it to be marginally capable of balancing radiative cooling.Comment: Accepted for publication in MNRAS, 18 pages, 9 postscript figures
Intermittent Preventive Treatment in Infants for the Prevention of Malaria in Rural Western Kenya: A Randomized, Double-Blind Placebo-Controlled Trial
Background
Intermittent preventive treatment in infants (IPTi) with sulphadoxine-pyrimethamine (SP) for the prevention of malaria has shown promising results in six trials. However, resistance to SP is rising and alternative drug combinations need to be evaluated to better understand the role of treatment versus prophylactic effects.
Methods
Between March 2004 and March 2008, in an area of western Kenya with year round malaria transmission with high seasonal intensity and high usage of insecticide-treated nets, we conducted a randomized, double-blind placebo-controlled trial with SP plus 3 days of artesunate (SP-AS3), 3 days of amodiaquine-artesunate (AQ3-AS3), or 3 days of short-acting chlorproguanil-dapsone (CD3) administered at routine expanded programme of immunization visits (10 weeks, 14 weeks and 9 months).
Principal Findings
1,365 subjects were included in the analysis. The incidence of first or only episode of clinical malaria during the first year of life (primary endpoint) was 0.98 episodes/person-year in the placebo group, 0.74 in the SP-AS3 group, 0.76 in the AQ3-AS3 group, and 0.82 in the CD3 group. The protective efficacy (PE) and 95% confidence intervals against the primary endpoint were: 25.7% (6.3, 41.1); 25.9% (6.8, 41.0); and 16.3% (−5.2, 33.5) in the SP-AS3, AQ3-AS3, and CD3 groups, respectively. The PEs for moderate-to-severe anaemia were: 27.5% (−6.9, 50.8); 23.1% (−11.9, 47.2); and 11.4% (−28.6, 39.0). The duration of the protective effect remained significant for up to 5 to 8 weeks for SP-AS3 and AQ3-AS3. There was no evidence for a sustained beneficial or rebound effect in the second year of life. All regimens were well tolerated.
Conclusions
These results support the view that IPTi with long-acting regimens provide protection against clinical malaria for up to 8 weeks even in the presence of high ITN coverage, and that the prophylactic rather than the treatment effect of IPTi appears central to its protective efficacy
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