598 research outputs found
Observation of Galactic Sources of Very High Energy Gamma-Rays with the MAGIC Telescope
The MAGIC telescope with its 17m diameter mirror is today the largest
operating single-dish Imaging Air Cherenkov Telescope (IACT). It is located on
the Canary Island La Palma, at an altitude of 2200m above sea level, as part of
the Roque de los Muchachos European Northern Observatory. The MAGIC telescope
detects celestial very high energy gamma-radiation in the energy band between
about 50 GeV and 10 TeV. Since the autumn of 2004 MAGIC has been taking data
routinely, observing various objects, like supernova remnants (SNRs), gamma-ray
binaries, Pulsars, Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRB). We
briefly describe the observational strategy, the procedure implemented for the
data analysis, and discuss the results of observations of Galactic Sources.Comment: Brief Review, to be pulished in: Mod. Phys. Lett.
XMM-Newton observations of the supernova remnant IC443: I. soft X-ray emission from shocked interstellar medium
The shocked interstellar medium around IC443 produces strong X-ray emission
in the soft energy band (E<1.5 keV). We present an analysis of such emission as
observed with the EPIC MOS cameras on board the XMM-Newotn observatory, with
the purpose to find clear signatures of the interactions with the interstellar
medium (ISM) in the X-ray band, which may complement results obtained in other
wavelenghts. We found that the giant molecular cloud mapped in CO emission is
located in the foreground and gives an evident signature in the absorption of
X-rays. This cloud may have a torus shape and the part of torus interacting
with the IC443 shock gives rise to 2MASS-K emission in the southeast. The
measured density of emitting X-ray shocked plasma increases toward the
northeastern limb, where the remnant is interacting with an atomic cloud. We
found an excellent correlation between emission in the 0.3-0.5 keV band and
bright optical/radio filament on large spatial scales. The partial shell
structure seen in this band therefore traces the encounter with the atomic
cloud.Comment: 10 pages, 10 figures, accepted for publication in ApJ (20 September
2006, v649). For hi-res figures, see
http://www.astropa.unipa.it/Library/OAPA_preprints/ic443ele1.ps.g
Asymmetric Patterns of Visual Field Defect in Primary Open-Angle and Primary Angle-Closure Glaucoma
Purpose: To compare the hemifield asymmetry of visual field (VF) loss in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG) across all severity levels.
Methods: A total of 522 eyes of 327 patients with POAG (mean age ± SD, 54.1 ± 12.4 years) and 375 eyes of 204 patients with PACG (67.3 ± 8.9 years) were included. Subjects meeting the definitions of POAG or PACG were included. Means of the total deviation (TD) values (Humphrey 24-2 VF) in the Glaucoma Hemifield Test (GHT) regions were calculated in early (â„ â6 dB), moderate (< â6 dB and â„ â12 dB), and advanced (< â12 dB) stages of POAG and PACG eyes. Then the differences of the TD values between superior and inferior hemifield GHT regions of POAG and PACG eyes were calculated. Also, the relationship between the values of pattern SD (PSD) and mean TD (mTD) was compared between POAG and PACG.
Results: In POAG eyes in the early stage, three regions (central, paracentral, and peripheral) in the superior hemifield had greater loss than their inferior counterparts; in moderate and advanced stages, all GHT regions in the superior hemifield had greater loss than their inferior counterparts. In PACG eyes, siginificantly fewer regions in the superior hemifield were significantly worse than their inferior counterpart, compared with POAG: one region (central) in early stage, two regions (central and peripheral) in moderate stage, and one region (central) in advanced stage. POAG eyes had greater PSD values than PACG eyes for given mean of TD values.
Conclusions: In both POAG and PACG eyes, VF damage was more pronounced in superior hemifield than inferior hemifield; however, this tendency was more obvious in POAG eyes than in PACG eyes
Accretion Disk Spectra of the Ultra-luminous X-ray Sources in Nearby Spiral Galaxies and Galactic Superluminal Jet Sources
Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and
Galactic superluminal jet sources share the common spectral characteristic that
they have unusually high disk temperatures which cannot be explained in the
framework of the standard optically thick accretion disk in the Schwarzschild
metric. On the other hand, the standard accretion disk around the Kerr black
hole might explain the observed high disk temperature, as the inner radius of
the Kerr disk gets smaller and the disk temperature can be consequently higher.
However, we point out that the observable Kerr disk spectra becomes
significantly harder than Schwarzschild disk spectra only when the disk is
highly inclined. This is because the emission from the innermost part of the
accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen
for a face-on disk. The Galactic superluminal jet sources are known to be
highly inclined systems, thus their energy spectra may be explained with the
standard Kerr disk with known black hole masses. For ULXs, on the other hand,
the standard Kerr disk model seems implausible, since it is highly unlikely
that their accretion disks are preferentially inclined, and, if edge-on Kerr
disk model is applied, the black hole mass becomes unreasonably large (> 300
M_solar). Instead, the slim disk (advection dominated optically thick disk)
model is likely to explain the observed super-Eddington luminosities, hard
energy spectra, and spectral variations of ULXs. We suggest that ULXs are
accreting black holes with a few tens of solar mass, which is not unexpected
from the standard stellar evolution scenario, and that their X-ray emission is
from the slim disk shining at super-Eddington luminosities.Comment: ApJ, accepte
ASCA Observations of the Supernova Remnant IC 443: Thermal Structure and Detection of Overionized Plasma
We present the results of X-ray spatial and spectral studies of the
``mixed-morphology'' supernova remnant IC 443 using ASCA. IC 443 has a
center-filled image in X-ray band, contrasting with the shell-like appearance
in radio and optical bands. The overall X-ray emission is thermal, not from a
synchrotron nebula. ASCA observed IC 443 three times, covering the whole
remnant. From the image analysis, we found that the softness-ratio map reveals
a shell-like structure. At the same time, its spectra require two (1.0 keV and
0.2 keV) plasma components; the emission of the 0.2 keV plasma is stronger in
the region near the shell than the center. These results can be explained by a
simple model that IC 443 has a hot (1.0 keV) interior surrounded by a cool (0.2
keV) outer shell. From the emission measures, we infer that the 0.2 keV plasma
is denser than the 1.0 keV plasma, suggesting pressure equilibrium between the
two. In addition, we found that the ionization temperature of sulfur, obtained
from H-like K to He-like K intensity ratio, is 1.5 keV,
significantly higher than the gas temperature of 1.0 keV suggested from the
continuum spectrum. The same can be concluded for silicon. Neither an
additional, hotter plasma component nor a multi-temperature plasma successfully
accounts for this ratio, and we conclude that the 1.0 keV plasma is
overionized. This is the first time that overionized gas has been detected in a
SNR. For the gas to become overionized in the absence of a photoionizing flux,
it must cool faster than the ions recombine. Thermal conduction from the 1.0
keV plasma to the 0.2 keV one could cause the 1.0 keV plasma to become
overionized, which is plausible within an old (3 yr) SNR.Comment: 11 pages, 15 figures, 2 tables, accepted for publication in The
Astrophysical Journa
A Bow Shock Nebula Around a Compact X-Ray Source in the Supernova Remnant IC443
We present spectra and high resolution images of the hard X-ray feature along
the southern edge of the supernova remnant IC443. Data from the Chandra X-ray
Observatory reveal a comet-shaped nebula of hard emission, which contains a
softer point source at its apex. We also present 20cm, 6cm, and 3.5cm images
from the Very Large Array that clearly show the cometary nebula. Based on the
radio and X-ray morphology and spectrum, and the radio polarization properties,
we argue that this object is a synchrotron nebula powered by the compact source
that is physically associated with IC443. The spectrum of the soft point source
is adequately but not uniquely fit by a black body model (kT=0.71 +/- 0.08 keV,
L=(6.5 +/- 0.9) * 10^31 erg/s). The cometary morphology of the nebula is the
result of the supersonic motion of the neutron star (V_NS=250 +/- 50 km/s),
which causes the relativistic wind of the pulsar to terminate in a bow shock
and trail behind as a synchrotron tail. This velocity is consistent with an age
of 30,000 years for the SNR and its associated neutron star.Comment: 9 pages, 5 figures, accepted for publication in the ApJ Letter
Conceptual Design of a Fast-Ignition Laser Fusion Reactor FALCON-D
A new conceptual design of the laser fusion power plant FALCON-D (Fast ignition Advanced Laser fusion reactor CONcept with a Dry wall chamber) has been proposed. The fast ignition method can achieve the sufficient fusion gain for a commercial operation (~100) with about 10 times smaller fusion yield than the conventional central ignition method. FALCON-D makes full use of this property and aims at designing with a compact dry wall chamber (5~6m radius). 1-D/2-D hydrodynamic simulations showed the possibility of the sufficient gain achievement with a 40 MJ target yield. The design feasibility of the compact dry wall chamber and solid breeder blanket system was shown through the thermomecanical analysis of the dry wall and neutronics analysis of the blanket system. A moderate electric output (~400MWe) can be achieved with a high repetition (30Hz) laser. This dry wall concept not only reduces some difficulties accompanied with a liquid wall but also enables a simple cask maintenance method for the replacement of the blanket system, which can shorten the maintenance time. The basic idea of the maintenance method for the final optics system has also been proposed. Some critical R&D issues required for this design are also discussed
A Statistical Analysis of Supersymmetric Dark Matter in the MSSM after WMAP
We study supersymmetric dark matter in the general flavor diagonal MSSM by
means of an extensive random scan of its parameter space. We find that, in
contrast with the standard mSUGRA lore, the large majority of viable models
features either a higgsino or a wino-like lightest neutralino, and yields a
relic abundance well below the WMAP bound. Among the models with neutralino
relic density within the WMAP range, higgsino-like neutralinos are still
dominant, though a sizeable fraction of binos is also present. In this latter
case, relic density suppression mechanisms are shown to be essential in order
to obtain the correct neutralino abundance. We then carry out a statistical
analysis and a general discussion of neutralino dark matter direct detection
and of indirect neutralino detection at neutrino telescopes and at antimatter
search experiments. We point out that current data exclude only a marginal
portion of the viable parameter space, and that models whose thermal relic
abundance lies in the WMAP range will be significantly probed only at future
direct detection experiments. Finally, we emphasize the importance of relic
density enhancement mechanisms for indirect detection perspectives, in
particular at future antimatter search experiments.Comment: 39 pages, 25 figure
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