Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for ...the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.
We present observations of the young supernova remnant (SNR) RX J1713.7--3946 with the Fermi Large Area Telescope (LAT). We clearly detect a source positionally coincident with the SNR. The source is ...extended with a best-fit extension of 055 ? 004 matching the size of the non-thermal X-ray and TeV gamma-ray emission from the remnant. The positional coincidence and the matching extended emission allow us to identify the LAT source with SNR RX J1713.7--3946. The spectrum of the source can be described by a very hard power law with a photon index of Delta *G = 1.5 ? 0.1 that coincides in normalization with the steeper H.E.S.S.-detected gamma-ray spectrum at higher energies. The broadband gamma-ray emission is consistent with a leptonic origin as the dominant mechanism for the gamma-ray emission.
Recent detections of the starburst galaxies M82 and NGC 253 by gamma-ray telescopes suggest that galaxies rapidly forming massive stars are more luminous at gamma-ray energies compared to their ...quiescent relatives. Building upon those results, we examine a sample of 69 dwarf, spiral, and luminous and ultraluminous infrared galaxies at photon energies 0.1-100 GeV using 3 years of data collected by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). Measured fluxes from significantly detected sources and flux upper limits for the remaining galaxies are used to explore the physics of cosmic rays in galaxies. We find further evidence for quasi-linear scaling relations between gamma-ray luminosity and both radio continuum luminosity and total infrared luminosity which apply both to quiescent galaxies of the Local Group and low-redshift starburst galaxies (conservative P-values > ~0.05 accounting for statistical and systematic uncertainties). The normalizations of these scaling relations correspond to luminosity ratios of log (L sub(0.1,100 GeV)/L sub(1.4 GHz)) = 1.7 + or - 0.1 sub((statistical)) + or - 0.2 sub((dispersion)) and log (L sub(0.1-100 GeV)/L sub(8,1000 mu m)) = -4.3 + or - 0.1 sub((statistical)) + or - 0.2 sub((dispersion)) for a galaxy with a star formation rate of 1 M sub(middot in circle) yr super(-1), assuming a Chabrier initial mass function. Using the relationship between infrared luminosity and gamma-ray luminosity, the collective intensity of unresolved star-forming galaxies at redshifts 0 > z > 2.5 above 0.1 GeV is estimated to be 0.4-2.4 x 10 super(-6) ph cm super(-2) s super(-1) sr super(-1) (4%-23% of the intensity of the isotropic diffuse component measured with the LAT). We anticipate that ~10 galaxies could be detected by their cosmic-ray-induced gamma-ray emission during a 10 year Fermi mission.
The Large Area Telescope (Fermi/LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view (FoV), high-energy gamma -ray ...telescope, covering the energy range from below 20 MeV to more than 300 GeV. The LAT was built by an international collaboration with contributions from space agencies, high-energy particle physics institutes, and universities in France, Italy, Japan, Sweden, and the United States. This paper describes the LAT, its preflight expected performance, and summarizes the key science objectives that will be addressed. On-orbit performance will be presented in detail in a subsequent paper. The LAT is a pair-conversion telescope with a precision tracker and calorimeter, each consisting of a 4 X 4 array of 16 modules, a segmented anticoincidence detector that covers the tracker array, and a programmable trigger and data acquisition system. Each tracker module has a vertical stack of 18 (x, y) tracking planes, including two layers (x and y) of single-sided silicon strip detectors and high-Z converter material (tungsten) per tray. Every calorimeter module has 96 CsI(Tl) crystals, arranged in an eight-layer hodoscopic configuration with a total depth of 8.6 radiation lengths, giving both longitudinal and transverse information about the energy deposition pattern. The calorimeter's depth and segmentation enable the high-energy reach of the LAT and contribute significantly to background rejection. The aspect ratio of the tracker (height/width) is 0.4, allowing a large FoV (2.4 sr) and ensuring that most pair-conversion showers initiated in the tracker will pass into the calorimeter for energy measurement. Data obtained with the LAT are intended to (1) permit rapid notification of high-energy gamma -ray bursts and transients and facilitate monitoring of variable sources, (2) yield an extensive catalog of several thousand high-energy sources obtained from an all-sky survey, (3) measure spectra from 20 MeV to more than 50 GeV for several hundred sources, (4) localize point sources to 0.3-2 arcmin, (5) map and obtain spectra of extended sources such as SNRs, molecular clouds, and nearby galaxies, (6) measure the diffuse isotropic gamma -ray background up to TeV energies, and (7) explore the discovery space for dark matter.
ABSTRACT
We present a catalog of high-energy gamma-ray sources detected by the Large Area
Telescope (LAT), the primary science instrument on the
Fermi Gamma-ray
Space Telescope (Fermi)
, during the ...first 11 months of the science
phase of the mission, which began on 2008 August 4. The First
Fermi
-LAT catalog (1FGL) contains 1451 sources detected and
characterized in the 100 MeV to 100 GeV range. Source detection was based on the
average flux over the 11 month period, and the threshold likelihood Test
Statistic is 25, corresponding to a significance of just over 4σ. The 1FGL
catalog includes source location regions, defined in terms of elliptical fits to
the 95% confidence regions and power-law spectral fits as well as flux
measurements in five energy bands for each source. In addition, monthly light
curves are provided. Using a protocol defined before launch we have tested for
several populations of gamma-ray sources among the sources in the catalog. For
individual LAT-detected sources we provide firm identifications or plausible
associations with sources in other astronomical catalogs. Identifications are
based on correlated variability with counterparts at other wavelengths, or on
spin or orbital periodicity. For the catalogs and association criteria that we
have selected, 630 of the sources are unassociated. Care was taken to
characterize the sensitivity of the results to the model of interstellar diffuse
gamma-ray emission used to model the bright foreground, with the result that 161
sources at low Galactic latitudes and toward bright local interstellar clouds
are flagged as having properties that are strongly dependent on the model or as
potentially being due to incorrectly modeled structure in the Galactic diffuse
emission.
ABSTRACT
We report observation of the supernova remnant (SNR) IC 443 (G189.1+3.0) with the
Fermi Gamma-ray Space Telescope
Large Area Telescope (LAT) in the energy band between 200 MeV and 50 GeV. ...IC 443 is a shell-type SNR with mixed morphology located off the outer Galactic plane where high-energy emission has been detected in the X-ray, GeV and TeV gamma-ray bands. Past observations suggest IC 443 has been interacting with surrounding interstellar matter. Proximity between dense shocked molecular clouds and GeV–TeV gamma-ray emission regions detected by
EGRET
,
MAGIC
, and
VERITAS
suggests an interpretation that cosmic-ray (CR) particles are accelerated by the SNR. With the high gamma-ray statistics and broad energy coverage provided by the LAT, we accurately characterize the gamma-ray emission produced by the CRs accelerated at IC 443. The emission region is extended in the energy band with θ
68
= 0.°27 ± 0.°01(stat) ± 0.°03(sys) for an assumed two-dimensional Gaussian profile and overlaps almost completely with the extended source region of
VERITAS
. Its centroid is displaced significantly from the known pulsar wind nebula (PWN) which suggests the PWN is not the major contributor in the present energy band. The observed spectrum changes its power-law slope continuously and continues smoothly to the
MAGIC
and
VERITAS
data points. The combined gamma-ray spectrum (200 MeV <
E
< 2 TeV) is reproduced well by decays of neutral pions produced by a broken power-law proton spectrum with a break around 70 GeV.
We investigate the time-dependent behaviour of Crab-like pulsar wind nebulae (PWNe) generating a set of models using four different initial spin-down luminosities (L0 = ...1, 0.1, 0.01, 0.001... x ...L0,Crab), eight values of magnetic fraction (... = 0.001, 0.01, 0.03, 0.1, 0.5, 0.9, 0.99 and 0.999, i.e. from fully particle dominated to fully magnetically dominated nebulae) and three distinctive ages: 940, 3000 and 9000 years. We find that the self-synchrotron Compton (SSC) contribution is irrelevant for LSD = 0.1, 1 and 10 per cent of the Crab power, disregarding the age and the magnetic fraction. SSC only becomes relevant for highly energetic (~70 per cent of the Crab), particle dominated nebulae at low ages (of less than a few kyr), located in a far-infrared (FIR) background with relatively low energy density. Since no pulsar other than Crab is known to have these features, these results clarify why the Crab nebula, and only it, is SSC dominated. No young PWN would be detectable at TeV energies if the pulsar's spin-down power is 0.1 per cent Crab or lower. For 1 per cent of the Crab spin-down, only particle-dominated nebulae can be detected by HESS-like telescopes when young enough (with details depending on the precise injection and environmental parameters). Above 10 per cent of the Crab's power, all PWNe are detectable by HESS-like telescopes if they are particle dominated, no matter the age. The impact of the magnetic fraction on the final spectral energy distribution is varied and important, generating order of magnitude variations in the luminosity output for systems that are otherwise the same (equal P, ..., injection and environment). (ProQuest: ... denotes formulae/symbols omitted.)
We make a time-dependent characterization of pulsar wind nebulae (PWNe) surrounding some of the highest spin-down pulsars that have not yet been detected at TeV. Our aim is assessing their possible ...level of magnetization. We analyse the nebulae driven by J2022+3842 in G76.9+1.0, J0540-6919 in N158A (the Crab twin), J1400−6325 in G310.6−1.6, and J1124−5916 in G292.0+0.18, none of which have been found at TeV energies. For comparison, we refer to published models of G54.1+0.3, the Crab nebula, and develop a model for N157B in the Large Magellanic Cloud (LMC). We conclude that further observations of N158A could lead to its detection at VHE. According to our model, a far-infrared energy density of 5 eV cm−3 could already lead to a detection in H.E.S.S. (assuming no other IC target field) within 50 h of exposure, and just the cosmic microwave background inverse Compton contribution would produce VHE photons at the CTA sensitivity. We also propose models for G76.9+1.0, G310.6−1.6 and G292.0+1.8 which suggest their TeV detection in a moderate exposure for the latter two with the current generation of Cherenkov telescopes. We analyse the possibility that these PWNe are highly magnetized, where the low number of particles explains the residual detection in X-rays and their lack of detection at TeV energies.
Abstract Glycogen storage diseases (GSD) are inherited metabolic disorders of glycogen metabolism due to intracellular enzyme deficiency resulting in abnormal storage of glycogen in tissues. GSD ...represents an indication for liver transplantation (OLT) when medical treatment fails to control the metabolic dysfunction and/or there is an high risk of malignant transformation of hepatocellular adenomas (HCA). Herein we have reported two cases of GSD, type Ia and type VI, which were both associated with rapidly growing HCA, and underwent OLT because of suspect changes in their radiological features. Final histological findings in the explanted liver showed the presence of hepatocellular carcinoma (HCC) in both cases. In GSD type Ia and VI, OLT is considered to be the treatment of choice when a liver neoplasm is suspected. While the association of HCC with GSD type Ia is well known, this is the first case of HCC in GSD type VI so far reported to the best of our knowledge.
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