Absorption of High Energy Gamma-Rays by Low Energy Intergalactic Photons

Following our previously proposed technique, we have used the recent gamma-ray observations of Mrk 421 to place theoretically significant constraints on and possible estimates of the intergalactic infrared radiation field (IIRF) which are consistent with normal galactic IR production by stars and dust and rule out exotic mechanisms proposed to produce a larger IIRF. Using models for the low energy intergalactic photon spectrum from microwave to UV energies, we calculate the opacity of inter- galactic space to gamma-rays as a function of energy and redshift. These calculations indicate that the GeV gamma-ray burst recently observed by the EGRET experiment on CGRO originates at a redshift less than approximately 1.5.Comment: 12 pg., uuencoded, Z-compressed ps file (includes figures), To be published in Space Sci. Re

The galactic halo question: New size constraints from galactic gamma-ray data

The SAS-2 gamma-ray data is analyzed making use of recent CO line emission and other data for determining the large-scale distribution of galactic gas. A nonuniform distribution of cosmic rays in the galaxy is implied. This fact rules out large trapping halo models and extragalactic origin models. Detailed models of diffusion halos of various sizes perpendicular to the galactic plane are considered. In such models, the scale perpendicular to the plane has a strong effect in determining the radial distribution of cosmic rays. Such radial distributions are calculated for cylindrical coordinate models. The implied gamma-ray longitude distributions are then calculated and compared with the SAS-2 data for goodness-of-fit. Assuming the sources to be supernova remnants or pulsars, cosmic ray nucleon halo models with scale heights greater than 3 kpc are found to provide a poor fit to the gamma-ray longitude data (probability of 6% or less). Thin halo, or source dominated diffusion models are found to provide a good fit to the gamma-ray data, with an upper limit scale height of approximately 3 kpc

Comment on ``Cosmological Gamma Ray Bursts and the Highest Energy Cosmic Rays''

In a letter with the above title, published some time ago in PRL, Waxman made the interesting suggestion that cosmological gamma ray bursts (GRBs) are the source of the ultra high energy cosmic rays (UHECR). This has also been proposed independently by Milgrom and Usov and by Vietri. However, recent observations of GRBs and their afterglows and in particular recent data from the Akeno Great Air Shwoer Array (AGASA) on UHECR rule out extragalactic GRBs as the source of UHECR.Comment: Comment on a letter with the above title published by E. Waxman in PRL 75, 386 (1995). Submitted for publication in PRL/Comment

Participatory evaluation in community development : an inquiry into indigenous evaluation among the Gbaya of the Central African Republic.

Participation in community development work has been emphasized since the late 1960\u27s; Participatory Evaluation (PE), however, was not introduced until the mid-1970\u27s. At about that same time, Participatory Research (PR) was seeking to help shift the ownership and control of community development work and social research back into the hands of the local community. One important contribution of PR, has been the recognition of the importance of indigenous knowledge. As indigenous knowledge and indigenous practices were being recovered by communities during PR, it soon became evident that the Western model of development--and its emphasis on the transfer of Western technological knowledge--was often insufficient, inappropriate, or culturally unacceptable. Although evaluation practitioners increased the participation of the local community in the evaluation of its own development work, PE was often limited to participation-in-evaluation (PiE). The ownership and control of the evaluation process often stayed within the hands of the evaluation experts often using Western evaluation methods. The first part of the study examines the emergence and evolution of PE in community development work during the past three decades. The study then explores the indigenous evaluation practices of the Gbaya people of western Central African Republic, where the researcher has lived and worked with health and community development since 1982. Ethnographic interviewing of key informants explored the following questions: What are the indigenous evaluation practices of the Gbaya? How is information gathered and used? Who can be involved in decision-making, in what contexts? The study further investigates Gbaya forms of evaluation through the participant observation of the participatory evaluation of a Lutheran church-sponsored development program in western Central African Republic. A framework for better understanding PE, including the factors of power , facilitation methods , and previous training and experience , are also presented. Using criteria from the framework, the following sub-categories of PE are offered: Participation-in-Evaluation (PiE), Less Participatory Evaluation (LPE), and Highly Participatory Evaluation (HiPE). Finally, a Gbaya Way of Decision-making is presented as one model of indigenous evaluation. This is followed by recommendations to practitioners of PE, as well as recommendations for the further research of Indigenous Evaluation

Molecular hydrogen in the galaxy and galactic gamma rays

Recent surveys of 2.6 mm CO emission and 100 MeV gamma-radiation in the galactic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H2 in the inner galaxy. Both the gamma ray and CO data suggest a prominent ring or arm consisting of cool clouds of H2 at a galactocentric distance of approximately 5 kpc with a mean density of approximately 4 atoms/cu cm. The importance of H2 in understanding galactic gamma ray observations is also reflected in the correlation of galactic latitude distribution of gamma rays and dense dust clouds. A detailed calculation of the gamma ray flux distribution in the 0 deg to 180 deg range using the CO data to obtain the average distribution of molecular clouds in the galaxy shows that most of the enhancement in the inner galaxy is due to pion-decay radiation and the 5 kpc ring plays a major role. Detailed agreement with the gamma ray data is obtained with the additional inclusion of contributions from bremsstrahlung and Compton radiation of secondary electrons and Compton radiation from the intense radiation field near the galactic center

Cosmological Cosmic Rays: Sharpening the Primordial Lithium Problem

Cosmic structure formation leads to large-scale shocked baryonic flows which are expected to produce a cosmological population of structure-formation cosmic rays (SFCRs). Interactions between SFCRs and ambient baryons will produce lithium isotopes via \alpha+\alpha \to ^{6,7}Li. This pre-Galactic (but non-primordial) lithium should contribute to the primordial 7Li measured in halo stars and must be subtracted in order to arrive to the true observed primordial lithium abundance. In this paper we point out that the recent halo star 6Li measurements can be used to place a strong constraint to the level of such contamination, because the exclusive astrophysical production of 6Li is from cosmic-ray interactions. We find that the putative 6Li plateau, if due to pre-Galactic cosmic-ray interactions, implies that SFCR-produced lithium represents Li_{SFCR}/Li_{plateau}\approx 15% of the observed elemental Li plateau. Taking the remaining plateau Li to be cosmological 7Li, we find a revised (and slightly worsened) discrepancy between the Li observations and Big Bang Nucleosynthesis predictions by a factor of ^7Li_{BBN}/^7Li_{plateau} \approx 3.7. Moreover, SFCRs would also contribute to the extragalactic gamma-ray background (EGRB) through neutral pion production. This gamma-ray production is tightly related to the amount of lithium produced by the same cosmic rays; the 6Li plateau limits the pre-Galactic (high-redshift) SFCR contribution to be at the level of I_{\pi_{\gamma}SFCR}/I_{EGRB} < 5% of the currently observed EGRB.Comment: 4 pages, accepted for publication in PR

Muon Detection of TeV Gamma Rays from Gamma Ray Bursts

Because of the limited size of the satellite-borne instruments, it has not been possible to observe the flux of gamma ray bursts (GRB) beyond GeV energy. We here show that it is possible to detect the GRB radiation of TeV energy and above, by detecting the muon secondaries produced when the gamma rays shower in the Earth's atmosphere. Observation is made possible by the recent commissioning of underground detectors (AMANDA, the Lake Baikal detector and MILAGRO) which combine a low muon threshold of a few hundred GeV or less, with a large effective area of 10^3 m^2 or more. Observations will not only provide new insights in the origin and characteristics of GRB, they also provide quantitative information on the diffuse infrared background.Comment: Revtex, 12 pages, 3 postscript figures, uses epsfig.st