Energetic Solar Flare X-Rays Observed by Satellite and Their Correlation with Solar Radio and Energetic Particle Emission

Abstract

view Abstract Citations (114) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Energetic Solar Flare X-Rays Observed by Satellite and Their Correlation with Solar Radio and Energetic Particle Emission Arnoldy, R. L. ; Kane, S. R. ; Winckler, J. R. Abstract Ionization chambers aboard the OGO-A and OGO-B spacecrafts with a response window for X-rays between 10 and 50 keY have accumulated more than 6000 hours of operation in space outside Earth's magnetosphere. Approximately thirty solar flare X-ray bursts have been detected between September 5, 1964, and June 20, 1966. These energetic X-ray bursts have been correlated with 3- and 10-cm solar radio emission and solar-flare electron and proton events measured in space. A proportionality is observed between the time-integrated X-ray and radio fluxes, and for a given flare the rise time, decay time, and total duration of the radio and X-ray bursts are similar. Exponential time constants between 1 and 10 mm characterize the decay. All 3- or 10-cm radio bursts greater than 80 flux units are accompanied by an X-ray event greater than 3 X 1O~ ergs cm~ sec', and the probability of detecting an X-ray event is negligible unless the radio spectrum includes the centrimetric range of wave- lengths. All but three of the X-ray events were correlated with SWF ionospheric disturbances. A number of large flare events occurred in which all of the energetic processes were observed; namely, solar protons, solar electrons, energetic bremsstrahlung, and high-frequency radio emission. In comparing energetic X-rays with solar particle emission the best correlation seems to exist with the solar electron events ob- served in space. Many solar proton events occurred without a detectable burst of energetic X-rays. It is shown that the results are consistent with a source in the flare region consisting of an active volume in a magnetic field containing hot or energetic electrons which lose energy predominantly by collisions with a much cooler gas and produce X-rays by bremsstrahlung. The similarity of decay and proportion- ality between the X-rays and microwaves suggests that the same electrons might produce both emissions About 5 X 10~ joules m~ (c/s)1 of microwave energy at Earth are required per electron at the Sun on the average. Physically acceptable choices of electron energy, collisional limited lifetime, and mag- netic field strength exist such that, with the assumption of synchrotron emission for the microwave radiation and bremsstrahlung for the X-rays, the observed proportionality between the two can be met A thermal source for the radio emission cannot, however, be excluded Publication: The Astrophysical Journal Pub Date: February 1968 DOI: 10.1086/149470 Bibcode: 1968ApJ...151..711A full text sources ADS |