Daniel J. H. Chung, Edward W. Kolb, Antonio Riotto Department of Physics and Enrico Fermi Institute The University of Chicago, Chicago, Illinois 60637-1433 NASA/Fermilab Astrophysics Center Fermilab National Accelerator Laboratory, Batavia, Illinois 60510-0500 Department of Astronomy and Astrophysics and Enrico Fermi Institute The University of Chicago, Chicago, Illinois 60637-1433 Theory Divis...

We present Chandra ACIS X-ray observations of the Galactic supernova remnant Cassiopeia A taken in December 2007. Combining these data with previous archival Chandra observations taken in 2000, 2002, and 2004, we estimate the remnant’s forward shock velocity at various points around the outermost shell to range between 4200 and 5200 ±500 km s. Using these results together with previous analyses...

A distinct low energy cosmic-ray component has been proposed to explain the essentially constant Be/Fe ratio at low metallicities. Atomic collisions of such low energy ions produce characteristic nonthermal X-ray emission. In this paper, we study the possible contribution of such X-rays to the Galactic ridge emission. We show that they would account for < ∼ 10% of the 10-60 keV luminosity of th...

We report the results of a search for > 20 keV photons from active stars using CGRO/BATSE Earth-occultation observations. Twelve of the \usual suspects" together with 12 \placebo" locations have been analyzed using the BATSE software for occultation analysis developed at NASA/MSFC. There are four detections at the nominal 5 level, and eight at the 3 level. However the strongest detection (that ...

We have calculated the Hα and Ca ii 8542Å line profiles based on four different atmospheric models, including the effects of nonthermal electron beams with various energy fluxes. These two lines have different responses to thermal and nonthermal effects, and can be used to diagnose the thermal and nonther-mal heating processes. We apply our method to an X-class flare that occurred on 2001 Octob...

In overdense plasma for which the plasma frequency exceeds the cyclotron frequency, X-mode, nearperpendicular cyclotron emission does not propagate to the outboard plasma edge. However, under these conditions it remains possible for electron Bernstein waves (EBWs) to transmit emitted radiation from central plasma to the plasma exterior via a mode conversion to electromagnetic waves near the pla...

In energetic nonthermal sources such as gamma-ray bursts, AGN or galactic jet sources, etc., one expects both relativistic and transrelativistic shocks acompanied by violent motions of moderately relativistic plasma. We present general considerations indicating that these sites are electron and positron accelerators leading to a modified power law spectrum. The electron (or e) energy index is v...

Nonthermal radiation is observed from clusters of galaxies in the radio, hard X-rays, and possibly in the soft X-ray/UV bands. While it is known that radiative processes related to nonthermal electrons are responsible for this radiation, the sites and nature of particle acceleration are not known. We investigate here the acceleration of protons and electrons in the shocks originated during merg...

We have done a spectroscopic study of the solar transition region using high resolution UV & EUV data obtained by SUMER(Solar Ultraviolet Measurements of Emitted Radiation) on board SOHO(Solar and Heliospheric Observatory). Optically thin and conspicuous emission lines observed at the solar limb are carefully selected to acquire average values of physical parameters for the quiet region as a fu...

We present the first observations of nonthermal decimetric burst emission of the Sun using the new 400 cm (74 MHz) system at the VLA. Our VLA observations were carried out in collaboration with the Large Angle Spectroscopic Coronagraph (LASCO) and the Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory spacecraft. Full-disk observations at 400 and 91 cm w...