Multiple Components in the Millimeter Emission of a Solar Flare

Abstract

We analyze a small are using imaging data at millimeter, microwave and soft X{ray wavelengths, and microwave and hard X{ray spectral observations. The remarkable aspect of this are is evidence for the presence of MeV{energy electrons, which are responsible for the nonthermal millimeter emission, at a time when no hard X{rays from lower{energy electrons are detected. This occurs during a smoothly varying phase which is seen at radio wavelengths to last several minutes and is the brightest phase at millimeter wavelengths, but is undetected in hard X{rays: it follows a brief spike of emission at are onset which has the more usual properties of impulsive events and features nonthermal microwave, millimeter and hard X{ray emission. We interpret the phase which is bright at millimeter wavelengths as due to e cient trapping of a relatively small number of nonthermal electrons, whereas during the hard X{ray emission trapping is much less e cient and the decay time is much shorter at all energies, leading to a larger ratio of hard X{ray ux to radio ux. As in

First detection of the impulsive and extended phases of a solar radio burst above 200 GHz

“…Such a B1-B2 time sequence has been already observed for a few events detected at 86 GHz (e.g. Kundu et al 1994;Raulin et al 1999). In the following, B1 and B2 are discussed separately.…”

“…2) are used to compute the expected microwave freefree emission for a source diameter ranging from 30 to 45 (typical sizes for 17 GHz thermal sources; e.g. Raulin et al 1999). The top panel of Rieger et al (1998) (triangles); the solid rectangle shows the domain of values deduced from the present radio observations for a magnetic field ranging from 300 G to 600 G (see text).…”

“…These calculations have been performed for: (i) a radio source size of 10 (typical size for millimeter sources, e.g. Raulin et al 1999 and references therein); (ii) a viewing angle θ = 45 • and (iii) an instantaneous isotropic distribution of radiating electrons with an energy spectrum taken as: N (E) = KE −δ (electrons MeV −1 ). The ratio 3ν B /2ν p (where ν p is the plasma frequency and ν B gyrofrequency) that governs the level of the Razin-Tsytovich suppression below ν max has been set to 1 for all values of B.…”

The Relationship Between Solar Radio and Hard X-ray Emission

“…Since the radio and HXR profiles are so similar, we cannot argue that the radio emission comes from a long-lived population of trapped electrons while the hard X-rays come from directly precipitating electrons, as occurs in other events where the time profiles clearly differ (e.g., Raulin et al 1999): the radio-emitting electrons have the same time behavior as the hard X-ray emitting electrons and should have a common origin and common evolution. There is a flattening in the RHESSI γ-ray spectra by about 0.5 in the index, but no sign in the data up to 8 MeV of the flattening by 2 implied by the radio data (Smith et al 2003), so we argue that the radio spectral indices in Figure 4.2 are not compatible with the RHESSI observations.…”

SYSTEM-ON-CHIP 36.8 GHZ RADIOMETER FOR SPACE-BASED OBSERVATION OF SOLAR FLARES: FEASIBILITY STUDY IN 0.25 μm SIGE BICMOS TECHNOLOGY

“…The magnetic energy is rapidly converted into thermal, kinetic and mechanical energies and the consequence is that the local plasma is heated to several tens of millions degrees, while particles are accelerated up to high energies. Flares are unique for the diversity of emission mechanism they exhibit and the broad range of wavelengths at which they radiate: from radiowave, millimeter-wave, soft and hard-X rays, up to γ-rays with energies reaching 1 Gev [15,16].…”