University of New Hampshire

About: University of New Hampshire is a education organization based out in Durham, New Hampshire, United States. It is known for research contribution in the topics: Population & Solar wind. The organization has 9379 authors who have published 24025 publications receiving 1020112 citations. The organization is also known as: UNH.

Gamma-ray line emission from SN1987A

Abstract: The gamma-ray spectrometer (GRS) on NASA's Solar Maximum Mission satellite (SMM) has observed a significant (>5δ) net line flux at ˜847 keV in the background-subtracted spectrum of SN1987A—accumulated between 1 August and 31 October 1987. This is the energy of the strong gamma-ray line from decay of 56Co, which was predicted1,3 to be seen from supernovae. The inferred average line flux during this period is ˜(1.0±0.25) x 10−3 photons cm−2 s−1 at an energy of 843 ± 5 keV. This feature cannot be explained by any statistical or systematic fluctuations observed in the seven previous years of GRS data. There is also evidence for the 1,238-keV line from 56Co decay, with an average flux of ∼(6±2)xlO−4 photons cm−2 s−1 The quoted photon fluxes for both lines are preliminary. This observation confirms that 56Co is present in the supernova ejecta (as implied by the light curve4,5) and that nucleosynthesis took place during the explosion. The first appearance of the gamma-ray lines was roughly coincident with the first detections of X-rays by Ginga and MIR6,7.

Coupled Hydromagnetic Wave Excitation and Ion Acceleration at an Evolving Coronal/Interplanetary Shock

Abstract: An analytical quasilinear theory is presented for the evolution of a "gradual" event consisting of solar energetic particles (SEPs) accelerated at an evolving coronal/interplanetary shock. The upstream ion transport is described by the two-stream moments of the focused transport equation, which accommodate the large streaming anisotropies observed near event onset. The proton transport equations and a wave kinetic equation are solved together for the coupled behavior of the hydromagnetic waves and the energetic protons. The theory includes diffusive shock acceleration, ion advection with the solar wind, spatial diffusion upstream of the shock, magnetic focusing, wave excitation by the energetic protons, and minor ions as test particles. A number of approximations are made for analytical tractability. The predictions reproduce the observed phases of most gradual SEP events: onset, a "plateau" with large streaming anisotropy, an "energetic storm particle" (ESP) enhancement prior to shock passage, and the decaying "invariant spectra" after shock passage. The theory treats naturally the transition from a scatter-dominated sheath adjacent to the shock where the wave intensity is enhanced to the nearly scatter-free ion transport in interplanetary space. The plateau is formed by ions that are extracted from the outer edge of the scatter-dominated sheath by magnetic focusing and escape into interplanetary space; it corresponds quantitatively to the "streaming limit" identified and interpreted in gradual events by D. V. Reames and C. K. Ng. The ion energy spectra at the shock have the standard power-law form dependent on shock strength, which is expected for diffusive shock acceleration, with a high-energy cutoff whose form is determined self-consistently by the ion escape rate. The increased shock strength, magnetic field magnitude, and injection energies close to the Sun account for the observed predominance of high-energy ions early in the event. The downstream ion transport is determined under two extreme assumptions: (i) vanishing diffusive transport and (ii) effective diffusive transport leading to small ion spatial gradients. The latter assumption reproduces the invariant spectra, spatial gradients, and exponential temporal decay observed in the late phase of many events. The minor ion distributions exhibit fractionation due to rigidity-dependent transport and acceleration. However, their energy spectra, spatial gradients, and high-energy cutoffs do not reproduce observed forms and lead to excessive fractionation. The origin of these discrepancies is probably the neglect of nonlinear processes. Although not easily incorporated in the theory, these processes could substantially modify the predicted wave intensity. An illustrative calculation assuming an arbitrary power-law form for the wave intensity demonstrates the sensitive dependence of ion fractionation on the power-law index.