Results 1 - 10 of 3185
Results 1 - 10 of 3185. Search took: 0.027 seconds
|Sort by: date | relevance|
[en] It is the purpose of the present paper to discuss in more detail the evidence for large scale correlations between the high-energy photon sky (/b/>100) and the known local distribution of diffuse interstellar matter. In particular, evidence will be presented of fairly detailed correlations with not only the Gould's Belt with its bright 'spots' in Orion and Ophiucus but also with an other local system, the so-called Dolidze Belt, recently found visible in the COS-B data base by Bignami
[en] The present assessment of the state-of-the-art in high energy gamma-ray source astronomy highlights the progress made by means of the COS-B mission. About 25 objects have been discovered with a sensitivity of 10 to the -10th ergs/sq cm per sec and an angular resolution of the order of 1 deg. It is noted, however, that angular resolution improvements of two orders of magnitude beyond those achieved by COS-B are required for further astronomical improvements. It is suggested that collimation could be introduced into the gamma-ray beam from the source. The only effective way of implementing such a scheme is through the use of a coded mask collimation technique
[en] Employing data collected during the first 25 months of observations by the Fermi-LAT, we describe and subsequently seek to model the very high energy (>300 MeV) emission from the central few parsecs of our Galaxy. We analyze the morphological, spectral, and temporal characteristics of the central source, 1FGL J1745.6-2900. The data show a clear, statistically significant signal at energies above 10 GeV, where the Fermi-LAT has angular resolution comparable to that of HESS at TeV energies. This makes a meaningful joint analysis of the data possible. Our analysis of the Fermi data (alone) does not uncover any statistically significant variability of 1FGL J1745.6-2900 at GeV energies on the month timescale. Using the combination of Fermi data on 1FGL J1745.6-2900 and HESS data on the coincident, TeV source HESS J1745-290, we show that the spectrum of the central gamma-ray source is inflected with a relatively steep spectral region matching between the flatter spectrum found at both low and high energies. We model the gamma-ray production in the inner 10 pc of the Galaxy and examine cosmic ray (CR) proton propagation scenarios that reproduce the observed spectrum of the central source. We show that a model that instantiates a transition from diffusive propagation of the CR protons at low energy to almost rectilinear propagation at high energies can explain well the spectral phenomenology. We find considerable degeneracy between different parameter choices which will only be broken with the addition of morphological information that gamma-ray telescopes cannot deliver given current angular resolution limits. We argue that a future analysis performed in combination with higher-resolution radio continuum data holds out the promise of breaking this degeneracy.
[en] From the earliest satellite measurements, it was clear that the high energy gamma ray sky was dominated by radiation from the galactic plane. The theoretical analyses of the time, and now, suggest that the majority of this radiation is diffuse, coming from cosmic ray interactions with the galactic matter and photons. The gamma ray measurements, therefore, provide the opportunity to gain significant additional insight into the galactic cosmic ray density distribution, the level of coupling of the cosmic rays and the matter, and, as it has developed, a better estimate of the molecular hydrogen density normalization. A cosmic ray density variation, at least broadly coupled to the galactic matter distribution, seems now to be supported by most of the analyses. This conclusion is consistent with the cosmic radiation being galactic and suggests the importance of future more sensitive gamma ray observations for the study of the detailed relationship between the cosmic rays and the galactic matter. An analysis of the radiation from high galactic latitudes suggest that, when the galactic radiation is subtracted, there is a residual isotropic radiation, which is believed to be extragalactic on origin. The diffuse gamma radiation from three local normal galaxies, the Small and Large Magellanic Clouds and M31, should be visible to at least one of the gamma ray telescopes on the Gamma Ray Observatory, and the first two should be seen by GAMMA-1. It is expected that the intensity and structure of both the Magellanic Clouds can be examined sufficiently well to study the cosmic ray density and thereby to determine the relevant scale of coupling for the cosmic rays and diffuse matter. (orig./WL)