Provider: - Institution: - Data provided by Europeana Collections- The Fermi Gamma-ray Space Telescope, which was launched by NASA in June 2008, is a
powerful space observatory which studies the ...high-energy gamma-ray sky Atwood (2009).
Fermi’s main instrument, the Large Area Telescope (LAT), detects photons in an energy range
between 20 MeV to greater than 300 GeV. The LAT is much more sensitive than its predecessor,
the EGRET telescope on the Compton Gamma Ray Observatory, and is expected to find
several thousand gamma-ray point sources, which is an order of magnitude more than its
predecessor EGRET Hartman et al. (1999).- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
The Fermi Gamma-ray Space Telescope, which was launched by NASA in June 2008, is a powerful space observatory which studies the high-energy gamma-ray sky Atwood (2009). Fermi’s main instrument, the ...Large Area Telescope (LAT), detects photons in an energy range between 20 MeV to greater than 300 GeV. The LAT is much more sensitive than its predecessor, the EGRET telescope on the Compton Gamma Ray Observatory, and is expected to find several thousand gamma-ray point sources, which is an order of magnitude more than its predecessor EGRET Hartman et al. (1999).
GALPROP is a numerical code for calculating the galactic propagation of relativistic charged particles and the diffuse emissions produced during their propagation. The code incorporates as much ...realistic astrophysical input as possible together with latest theoretical developments and has become a de facto standard in astrophysics of cosmic rays. We present GALPROP WebRun, a service to the scientific community enabling easy use of the freely available GALPROP code via web browsers. In addition, we introduce the latest GALPROP version 54, available through this service.
Methods based on hypothesis tests (HTs) in the Haar domain are widely used to
denoise Poisson count data. Facing large datasets or real-time applications,
Haar-based denoisers have to use the ...decimated transform to meet limited-memory
or computation-time constraints. Unfortunately, for regular underlying
intensities, decimation yields discontinuous estimates and strong "staircase"
artifacts. In this paper, we propose to combine the HT framework with the
decimated biorthogonal Haar (Bi-Haar) transform instead of the classical Haar.
The Bi-Haar filter bank is normalized such that the p-values of Bi-Haar
coefficients (pBH) provide good approximation to those of Haar (pH) for
high-intensity settings or large scales; for low-intensity settings and small
scales, we show that pBH are essentially upper-bounded by pH. Thus, we may
apply the Haar-based HTs to Bi-Haar coefficients to control a prefixed false
positive rate. By doing so, we benefit from the regular Bi-Haar filter bank to
gain a smooth estimate while always maintaining a low computational complexity.
A Fisher-approximation-based threshold imple- menting the HTs is also
established. The efficiency of this method is illustrated on an example of
hyperspectral-source-flux estimation.
Astrophys.J.652:L65-L68,2006; Erratum-ibid.664:L143,2007 We study the inverse Compton scattering of solar photons by Galactic
cosmic-ray electrons. We show that the gamma-ray emission from this ...process is
substantial with the maximum flux in the direction of the Sun; the angular
distribution of the emission is broad. This previously-neglected foreground
should be taken into account in studies of the diffuse Galactic and
extragalactic gamma-ray emission. Furthermore, observations by GLAST can be
used to monitor the heliosphere and determine the electron spectrum as a
function of position from distances as large as Saturn's orbit to close
proximity of the Sun, thus enabling unique studies of solar modulation. This
paves the way for the determination of other Galactic cosmic-ray species,
primarily protons, near the solar surface which will lead to accurate
predictions of gamma rays from pp-interactions in the solar atmosphere. These
albedo gamma rays will be observable by GLAST, allowing the study of deep
atmospheric layers, magnetic field(s), and cosmic-ray cascade development. The
latter is necessary to calculate the neutrino flux from pp-interactions at
higher energies (>1 TeV). Although this flux is small, it is a "guaranteed
flux" in contrast to other astrophysical sources of neutrinos, and may be
detectable by km^3 neutrino telescopes of the near future, such as IceCube.
Since the solar core is opaque for very high-energy neutrinos, directly
studying the mass distribution of the solar core may thus be possible.
This thesis presents the first large-scale CO J = 1 $\to$ 0 survey with sensitivity and angular resolution sufficient for study of individual giant molecular clouds in the Outer Arm of the Galaxy. ...Also analyzed here is the composite of all recent CO observations of the outer Galaxy with the CfA 1.2 m telescope. This data set covers nearly one-seventh of the Galactic equator and is the largest and most sensitive to date for study of the large-scale distribution of molecular gas in the outer Galaxy. The essential conclusion from the CO survey of the Outer Arm is that the Outer Arm is a well-defined, continuous feature in CO that contains GMCs as large as those in the inner Galaxy. The molecular clouds in the Arm do not appear deficient in massive star formation nor unusual in any way other than faint in CO for their H$\sb2$ content. Several lines of evidence support the assertion that the ratio of the column density of molecular hydrogen to the integrated intensity of the CO line, denoted X, is a factor of 4 larger in the Outer Arm than in the molecular ring, most importantly analysis of the luminosity-line width relation of individual clouds in the arm and comparison of the far-infrared emissivities of the dust associated with the atomic and molecular gas there. The observed distribution of CO in the outer Galaxy probably differs significantly from the distribution of IRAS point sources with infrared colors characteristic of star-forming regions. In particular, the radial extent of the CO distribution is greater than that of the point sources, especially if X increases markedly beyond the solar circle. However, the difference may be due only to inadequate observations of the point sources. The composite data show the increasing warp and flare of the plane beyond the solar circle and indicate significant CO emission to Galactocentric distance R = 14 kpc, the distribution of emission matching smoothly that known for the inner Galaxy. The analysis of the data is limited most by the requirement of extremely flat baselines in the observations. On the assumption X = 9.2 $\times$ 10$\sp{20}$ cm$\sp{-2}$ (K km s$\sp{-1}$)$\sp{-1}$ for R $\geq$ 12.5 kpc, the molecular mass extrapolated to the range R = 11$-$14 kpc is about 3 $\times$ 10$\sp8$ M$\sb\odot$, a significant fraction of the total molecular mass of the Galaxy, which may be estimated as 1.4 $\times$ 10$\sp9$ M$\sb\odot$, including a correction for helium.
We calculate the gamma-ray albedo flux from cosmic-ray (CR) interactions with the solid rock and ice in Main Belt asteroids (MBAs), Jovian and Neptunian Trojan asteroids, and Kuiper Belt objects ...(KBOs) using the Moon as a template. We show that the gamma-ray albedo for the Main Belt, Trojans, and Kuiper Belt strongly depends on the small-body size distribution of each system. Based on an analysis of the Energetic Gamma Ray Experiment Telescope (EGRET) data we infer that the diffuse emission from the MBAs, Trojans, and KBOs has an integrated flux of less than ~6x10^{-6} cm^{-2} s^{-1} (100-500 MeV), which corresponds to ~12 times the Lunar albedo, and may be detectable by the forthcoming Gamma Ray Large Area Space Telescope (GLAST). If detected by GLAST, it can provide unique direct information about the number of small bodies in each system that is difficult to assess by any other method. Additionally, the KBO albedo flux can be used to probe the spectrum of CR nuclei at close-to-interstellar conditions. The orbits of MBAs, Trojans, and KBOs are distributed near the ecliptic, which passes through the Galactic center and high Galactic latitudes. Therefore, the asteroid gamma-ray albedo has to be taken into account when analyzing weak gamma-ray sources close to the ecliptic, especially near the Galactic center and for signals at high Galactic latitudes, such as the extragalactic gamma-ray emission. The asteroid albedo spectrum also exhibits a 511 keV line due to secondary positrons annihilating in the rock. This may be an important and previously unrecognized celestial foreground for the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the Galactic 511 keV line emission including the direction of the Galactic center.
Astrophys.J. 621 (2005) L29-L32 For about two decades, a population of relative small and nearby molecular
clouds has been known to exist at high Galactic latitudes. Lying more than
10$^\circ$ from ...the Galactic plane, these clouds have typical distances of
$\sim$150 pc, angular sizes of $\sim1^\circ$, and masses of order tens of solar
masses. These objects are passive sources of high-energy $\gamma$-rays through
cosmic ray-gas interactions. Using a new wide-angle CO survey of the northern
sky, we show that typical high-latitude clouds are not bright enough in
$\gamma$-rays to have been detected by EGRET, but that of order 100 of them
will be detectable by the Large Area Telescope (LAT) on GLAST. Thus, we predict
a new steady population of $\gamma$-ray sources at high Galactic latitudes,
perhaps the most numerous after active galactic nuclei.
Diffuse emission is produced in energetic cosmic ray (CR) interactions, mainly protons and electrons, with the interstellar gas and radiation field and contains the information about particle spectra ...in distant regions of the Galaxy. It may also contain information about exotic processes such as dark matter annihilation, black hole evaporation etc. A model of the diffuse emission is important for determination of the source positions and spectra. Calculation of the Galactic diffuse continuum gamma-ray emission requires a model for CR propagation as the first step. Such a model is based on theory of particle transport in the interstellar medium as well as on many kinds of data provided by different experiments in Astrophysics and Particle and Nuclear Physics. Such data include: secondary particle and isotopic production cross sections, total interaction nuclear cross sections and lifetimes of radioactive species, gas mass calibrations and gas distribution in the Galaxy (H_2, H I, H II), interstellar radiation field, CR source distribution and particle spectra at the sources, magnetic field, energy losses, gamma-ray and synchrotron production mechanisms, and many other issues. We are continuously improving the GALPROP model and the code to keep up with a flow of new data. Improvement in any field may affect the Galactic diffuse continuum gamma-ray emission model used as a background model by the GLAST LAT instrument. Here we report about the latest improvements of the GALPROP and the diffuse emission model.
Methods based on hypothesis tests (HTs) in the Haar domain are widely used to denoise Poisson count data. Facing large datasets or real-time applications, Haar-based denoisers have to use the ...decimated transform to meet limited-memory or computation-time constraints. Unfortunately, for regular underlying intensities, decimation yields discontinuous estimates and strong "staircase" artifacts. In this paper, we propose to combine the HT framework with the decimated biorthogonal Haar (Bi-Haar) transform instead of the classical Haar. The Bi-Haar filter bank is normalized such that the p-values of Bi-Haar coefficients (pBH) provide good approximation to those of Haar (pH) for high-intensity settings or large scales; for low-intensity settings and small scales, we show that pBH are essentially upper-bounded by pH. Thus, we may apply the Haar-based HTs to Bi-Haar coefficients to control a prefixed false positive rate. By doing so, we benefit from the regular Bi-Haar filter bank to gain a smooth estimate while always maintaining a low computational complexity. A Fisher-approximation-based threshold imple- menting the HTs is also established. The efficiency of this method is illustrated on an example of hyperspectral-source-flux estimation.
PDF
