513 research outputs found
Evidence for GeV emission from the Galactic Center Fountain
The region near the Galactic center may have experienced recurrent episodes
of injection of energy in excess of 10 ergs due to repeated
starbursts involving more than 10 supernovae. This hypothesis can be
tested by measurements of -ray lines produced by the decay of
radioactive isotopes and positron annihilation, or by searches for pulsars
produced during starbursts. Recent OSSE observations of 511 keV emission
extending above the Galactic center led to the suggestion of a starburst driven
fountain from the Galactic center. We present EGRET observations that might
support this picture.Comment: 5 pages, 1 embedded Postscript figure. To appear in the Proceedings
of the Fourth Compton Symposiu
Introducing a new method for FDTD modeling of electromagnetic wave propagation in magnetized plasma
pre-printComputational investigations of electromagnetic wave propagation in the upper atmosphere are important for studying space weather hazards, such as geomagnetically induced currents (GICs). GICs are currents generated in gas/oil pipelines, railroads, and electric power networks due to solar storms and the consequent modification of the ionospheric current system. In the upper atmosphere where the collision frequency of the charged particles becomes negligible, the medium is magnetized and anisotropic. The difficulty in modeling wave propagation in magnetized plasma is due to the difficulty in accurately calculating the electric current. The electric current can be found from the momentum equation. However, a fast and efficient method is required to find the electric current perpendicular and parallel to the geomagnetic field
Effective Compton Cross Section in Non-Degenerate High Temperature Media
The effective compton cross section in a non-degenerate
plasma() is investigated in a
wide range of temperatures. The results show a decreasing behavior with
temperature especially for . The $may be important in
phenomena like accretion discs or ultra-relativistic blast waves in GRB models,
where the emitted radiation has to pass through a medium containing high energy
electrons.Comment: 12 pages, 7 figure
A Study on anisotropy of cosmic ray distribution with a small array of water-cherenkov detectors
The study of the anisotropy of the arrival directions is an essential tool to
investigate the origin and propagation of cosmic rays primaries. A simple way
of recording many cosmic rays is to record coincidences between a number of
detectors. We have monitored multi-TeV cosmic rays by a small array of water
cherenkov detectors in Tehran(35 43 N, 51 20 E, 1200m a.s.l). More than
1.1*10^6 extensive air shower events were recorded. In addition to the Compton-
Getting effect due to the motion of the earth in the Galaxy, an anisotropy has
been observed which is due to a unidirectional anisotropy of cosmic ray flow
along the Galactic arms.Comment: 16 pages 9 figs and one tabl
Evidence for a Galactic gamma ray halo
We present quantitative statistical evidence for a -ray emission halo
surrounding the Galaxy. Maps of the emission are derived. EGRET data were
analyzed in a wavelet-based non-parametric hypothesis testing framework, using
a model of expected diffuse (Galactic + isotropic) emission as a null
hypothesis. The results show a statistically significant large scale halo
surrounding the center of the Milky Way as seen from Earth. The halo flux at
high latitudes is somewhat smaller than the isotropic gamma-ray flux at the
same energy, though of the same order (O(10^(-7)--10^(-6)) ph/cm^2/s/sr above 1
GeV).Comment: Final version accepted for publication in New Astronomy. Some
additional results/discussion included, along with entirely revised figures.
19 pages, 15 figures, AASTeX. Better quality figs (PS and JPEG) are available
at http://tigre.ucr.edu/halo/paper.htm
The TIGRE gamma-ray telescope
TIGRE is an advanced telescope for gamma-ray astronomy with a few arcmin resolution. From 0.3 to 10 MeV it is a Compton telescope. Above 1 MeV, its multi-layers of double sided silicon strip detectors allow for Compton recoil electron tracking and the unique determination for incident photon direction. From 10 to 100 MeV the tracking feature is utilized for gamma-ray pair event reconstruction. Here we present TIGRE energy resolutions, background simulations and the development of the electronics readout system
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