LiBeB: High and low energy cosmic ray production and comparison with neutrino induced nucleosynthesis in SNII

We present new calculations of LiBeB production by accelerated particles with various compositions and energy spectra ranging from low energies to relativistic energies, and various ambient medium metallicities ($Z/Z_\odot$). The observed, essentially constant, Be/Fe ratio as a function of $Z/Z_\odot$ can be best understood if the metallicity of the accelerated particles (high energy or low energy) does not vary much with $Z/Z_\odot$. This could be achieved if the particles are accelerated directly from the ejecta of Type II supernovae (SNII) and not from the interstellar medium. Using the observed Be/Fe and the fact that most of the Fe at low $Z/Z_\odot$ is from SNII, we derive the energy content in accelerated particles per SNII (a few times 10$^{50}$ erg). We show that additional $^{11}$B production by neutrinos is consistent with the available data, allowing a neutrino yield from SNII less than or equal to the nominal published yields. We further show that the observed $^6$Li at low $Z/Z_\odot$ suggests that the accelerated particles responsible for the LiBeB at such $Z/Z_\odot$ are confined to low energies and have a relatively high He/O abundance.Comment: 9 pages with 4 emdedded figures, uuencoded, compressed, tared, style files included. In press Nuclei In the Cosmos, Nuclear Physics, Conference Proceeding

Electron-positron Annihilation Lines and Decaying Sterile Neutrinos

If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences. We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way center, and we thus obtain bounds on the sterile neutrino decay rate $\Gamma_e \ge 10^{-28}$ s$^{-1}$ from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of $1.2 \times 10^{-4}-9.7 \times 10^{-4}$ ph cm$^{-2}$ s$^{-1}$ from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate the flux of active neutrinos produced by sterile neutrino decays to be $0.02-0.1$ cm$^{-2}$ s$^{-1}$ passing through the earth.Comment: Accepted for publication in Astrophysics & Space Scienc

Heliospheric Transport of Neutron-Decay Protons

We report on new simulations of the transport of energetic protons originating from the decay of energetic neutrons produced in solar flares. Because the neutrons are fast-moving but insensitive to the solar wind magnetic field, the decay protons are produced over a wide region of space, and they should be detectable by current instruments over a broad range of longitudes for many hours after a sufficiently large gamma-ray flare. Spacecraft closer to the Sun are expected to see orders-of magnitude higher intensities than those at the Earth-Sun distance. The current solar cycle should present an excellent opportunity to observe neutron-decay protons with multiple spacecraft over different heliographic longitudes and distances from the Sun.Comment: 12 pages, 4 figures, to be published in special issue of Solar Physic

Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT

The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes, both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments in satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer (TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal counterpart only in the higher energy X- and gamma-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters were found difficult to be reconciled to a purely thermal emission component. We discuss possible mechanisms to explain the double spectral components at microwaves and in the THz ranges.Comment: Accepted version for publication in Solar Physic

Svestka's Research: Then and Now

Zdenek Svestka's research work influenced many fields of solar physics, especially in the area of flare research. In this article I take five of the areas that particularly interested him and assess them in a "then and now" style. His insights in each case were quite sound, although of course in the modern era we have learned things that he could not readily have envisioned. His own views about his research life have been published recently in this journal, to which he contributed so much, and his memoir contains much additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a contribution to a Topical Issue in Solar Physics, based on the presentations at this meeting (Editors Lyndsay Fletcher and Petr Heinzel

Microflares and the Statistics of X-ray Flares

This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal heating, either in active regions or in the quiet Sun.Comment: To be published in Space Science Reviews (2011

Nuclear gamma-ray lines in accretion source spectra

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

The pulsar contribution to the galactic gamma-ray emission

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe