1,392 research outputs found
Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background
The intergalactic magnetic field (IGMF) may leave an imprint on the angular
anisotropy of the extragalactic gamma-ray background through its effect on
electromagnetic cascades triggered by interactions between very high energy
photons and the extragalactic background light. A strong IGMF will deflect
secondary particles produced in these cascades and will thus tend to isotropize
lower energy cascade photons, thereby inducing a modulation in the anisotropy
energy spectrum of the gamma-ray background. Here we present a simple,
proof-of-concept calculation of the magnitude of this effect and demonstrate
that current Fermi data already seem to prefer non-negligible IGMF values. The
anisotropy energy spectrum of the Fermi gamma-ray background could thus be used
as a probe of the IGMF strength.Comment: 11 pages, 4 figures, MN LaTeX style; accepted for publication in
MNRA
The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST
The intrinsic distribution of spectral indices in GeV energies of
gamma-ray--loud blazars is a critical input in determining the spectral shape
of the unresolved blazar contribution to the diffuse extragalactic gamma-ray
background, as well as an important test of blazar emission theories. We
present a maximum-likelihood method of determining the intrinsic spectral index
distribution (ISID) of a population of gamma-ray emitters which accounts for
error in measurement of individual spectral indices, and we apply it to EGRET
blazars. We find that the most likely Gaussian ISID for EGRET blazars has a
mean of 2.27 and a standard deviation of 0.20. We additionally find some
indication that FSRQs and BL Lacs may have different ISIDs (with BL Lacs being
harder). We also test for spectral index hardening associated with blazar
variability for which we find no evidence. Finally, we produce simulated GLAST
spectral index datasets and perform the same analyses. With improved statistics
due to the much larger number of resolvable blazars, GLAST data will help us
determine the ISIDs with much improved accuracy. Should any difference exist
between the ISIDs of BL Lacs and FSRQs or between the ISIDs of blazars in the
quiescent and flaring states, GLAST data will be adequate to separate these
ISIDs at a significance better than 3 sigma.Comment: 11 pages, 9 figures, emulateapj; accepted for publication in Ap
Exploring Psalm 80 as a source for Matthew 25:31—46
The Sheep and the Goats passage, in Matthew 25:31—46, is the climax of Jesus’ fifth great discourse. A tapestry of rich images and titles are woven into this scene of judgment, in which the ‘Son of Man’ is an enthroned shepherd and king who will judge πάντα τὰ ἔθνη, placing the sheep at the preeminent right and the goats in condemnation at the left. Such an eclectic series of images and titles presents an opportunity for exploring the background sources for this passage.
This thesis argues that Psalm 80 (Psalm 79 LXX) is an important source for the composition of Matthew 25:31—46. Psalm 80 provides a religio—political background for understanding the devastation facing Judaism at the hands of the Romans. Viewing Psalm 80 as a source for Matthew 25:31—46 accounts for the diversity of images found in the Sheep and the Goats and provides further insight into the meaning of the passage. This reading of the Sheep and the Goats contends that the story is not focused on world—ending judgment. The text is describing a cataclysmic shift in which God’s vineyard has been taken from Israel and given to the church and the nations.
This research augments the larger corpus of Matthean studies, contributing to the less—prominent research of Psalm 80 as an influential text for multiple passages in the New Testament and other first century literature. Various studies have proposed the prevalence of Psalm 80, through scriptural ‘echoes’ and ‘allusions’ in the New Testament. This research seeks to solidify these hypotheses in favour of Psalm 80 as an important background text for the New Testament Gospels
The Effect of Blazar Spectral Breaks on the Blazar Contribution to the Extragalactic Gamma-ray Background
The spectral shapes of the contributions of different classes of unresolved
gamma-ray emitters can provide insight into their relative contributions to the
extragalactic gamma-ray background (EGB) and the natures of their spectra at
GeV energies. We calculate the spectral shapes of the contributions to the EGB
arising from BL Lacertae type objects (BL Lacs) and flat-spectrum radio quasars
(FSRQs) assuming blazar spectra can be described as broken power laws. We fit
the resulting total blazar spectral shape to the Fermi Large Area Telescope
measurements of the EGB, finding that the best-fit shape reproduces well the
shape of the Fermi EGB for various break scenarios. We conclude that a scenario
in which the contribution of blazars is dominant cannot be excluded on spectral
grounds alone, even if spectral breaks are shown to be common among Fermi
blazars. We also find that while the observation of a featureless (within
uncertainties) power-law EGB spectrum by Fermi does not necessarily imply a
single class of contributing unresolved sources with featureless individual
spectra, such an observation and the collective spectra of the separate
contributing populations determine the ratios of their contributions. As such,
a comparison with studies including blazar gamma-ray luminosity functions could
have profound implications for the blazar contribution to the EGB, blazar
evolution, and blazar gamma-ray spectra and emission.Comment: 8 pages, emulateapj format; 5 figures; accepted for publication in
Ap
Contribution to the Extragalactic Gamma-ray Background from the Cascades of Very-high Energy Gamma Rays
As very-high--energy photons propagate through the extragalactic background
light (EBL), they interact with the soft photons and initiate electromagnetic
cascades of lower energy photons and electrons. The collective intensity of a
cosmological population emitting at very-high energies (VHE) will be attenuated
at the highest energies through interactions with the EBL and enhanced at lower
energies by the resulting cascade. We calculate the cascade radiation created
by VHE photons produced by blazars and investigate the effects of cascades on
the collective intensity of blazars and the resulting effects on the
extragalactic gamma-ray background. We find that cascade radiation greatly
enhances the collective intensity from blazars at high energies before turning
over due to attenuation. The prominence of the resulting features depends on
the blazar gamma-ray luminosity function, spectral index distribution, and the
model of the EBL. We additionally calculate the cascade radiation from the
distinct spectral sub-populations of blazars, BL Lacertae objects (BL Lacs) and
flat-spectrum radio quasars (FSRQs), finding that the collective intensity of
BL Lacs is considerably more enhanced by cascade radiation than that of the
FSRQs due to their harder spectra. As such, studies of the blazar contribution
to the EGRB by Fermi will have profound implications for the nature of the EBL,
the evolution of blazars, and blazar spectra.Comment: 2009 Fermi Symposium, eConf Proceedings C09112
The Impact of Electromagnetic Cascades of Very-high Energy Gamma Rays on the Extragalactic Gamma-ray Background
As very high energy (VHE) photons propagate through the extragalactic background light (EBL), they interact with the soft photons of the EBL and initiate electromagnetic cascades of photons and electrons. The collective intensity of a cosmological population emitting at VHEs (such as blazars) will be attenuated at the highest energies through interactions with the EBL and enhanced at lower energies by the resulting cascade. As such, depending on the space density and spectra of the sources and the model of the EBL, cascade radiation can provide a significant contribution to the extragalactic gamma-ray background (EGB). Through deflections of the charged particles of the cascade, an intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the EGB. The impact of a strong IGMF is to isotropize lower energy cascade photons, inducing a modulation in the anisotropy energy spectrum of the EGB. We discuss the implications of cascade radiation for the origins of the EGB and the nature of the IGMF, as well as insight that will be provided by data from the Fermi Large Area Telescope in the upcoming years
The Multiwavelength View of Gamma-Ray Loud AGN
The gamma-ray sky observed by the Fermi Large Area Telescope (Fermi-LAT) encodes much information about the high-energy processes in the universe. Of the extragalactic sources sources resolved by the Fermi-LAT, blazars comprise the class of gamma-ray emitters with the largest number of identified members. Unresolved blazars are expected to contribute significantly to the diffuse extragalactic gamma-ray emission. However, blazars are also broadband emitters (from radio to TeV energies), and as such the multiwavelength study of blazars can provide insight into the high-energy processes of the universe
A Study Of Adult Education Programs In Thirty-Seven Schools And Colleges In Texas
There has always been some form of adult education. The nature of man was such that his environment, both natural and social became an educational force. This informal education was suitable to the simple and informed life of the past. But as society became more highly organized and complex, the gap between the informal education provided by the environment became wider and wider. The changes became so rapid and complex that even the formal education provided the youth was not adequate to the demands of adult life. So special agencies and programs were provided to supplement the education received by adults in their childhood and youth, and to provide retraining to meet the demands of an ever-changing society .
Theoretical Statements and Researches of Other Scholars:
The Federal Government took an active role in adult education for Negroes when it passed the Federal Emergency Educational Program in 1933.
Immediately Texas became interested in adult education for Negroes. Since 1936 the State Department of Education in Texas has shown a marked interest in public forums as a means of stimulating adult education for Negroes. The superintendents in the counties serve as forum counselors
Components of the Extragalactic Gamma Ray Background
We present new theoretical estimates of the relative contributions of
unresolved blazars and star-forming galaxies to the extragalactic gamma-ray
background (EGB) and discuss constraints on the contributions from alternative
mechanisms such as dark matter annihilation and truly diffuse gamma-ray
production. We find that the Fermi source count data do not rule out a scenario
in which the EGB is dominated by emission from unresolved blazars, though
unresolved star-forming galaxies may also contribute significantly to the
background, within order-of-magnitude uncertainties. In addition, we find that
the spectrum of the unresolved star-forming galaxy contribution cannot explain
the EGB spectrum found by EGRET at energies between 50 and 200 MeV, whereas the
spectrum of unresolved FSRQs, when accounting for the energy-dependent effects
of source confusion, could be consistent with the combined spectrum of the
low-energy EGRET EGB measurements and the Fermi-LAT EGB measurements.Comment: version accepted for publication in the Astrophysical Journa
New Theoretical Estimates of the Contribution of Unresolved Star-Forming Galaxies to the Extragalactic Gamma-Ray Background (EGB) as Measured by EGRET and the Fermi-LAT
We present new theoretical estimates of the contribution of unresolved star-forming galaxies to the extragalactic gamma-ray background (EGB) as measured by EGRET and the Fermi-LAT. We employ several methods for determining the star-forming galaxy contribution the the EGB, including a method positing a correlation between the gamma-ray luminosity of a galaxy and its rate of star formation as calculated from the total infrared luminosity, and a method that makes use of a model of the evolution of the galaxy gas mass with cosmic time. We find that depending on the model, unresolved star-forming galaxies could contribute significantly to the EGB as measured by the Fermi-LAT at energies between approx. 300 MeV and approx. few GeV. However, the overall spectrum of unresolved star-forming galaxies can explain neither the EGRET EGB spectrum at energies between 50 and 200 MeV nor the Fermi-LAT EGB spectrum at energies above approx. few GeV
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