Properties of Fast Submillimeter Time Structures during a Large Solar Flare

Abstract

We report properties of fast varying submillimeter emission during one of the strongest solar radio flares of solar cycle 23. Emission was obtained by the Solar Submillimeter-Wave Telescope at 212 and 405 GHz and compared with hard X-ray and-ray counts up to few tens of MeV photon energy ranges. We employ different methods to detect and characterize flux density variations and find that during the impulsive phase of the event, the closer in time to the peak flare, the higher the occurrence of the fastest and brightest time structures. The good comparison with hard X-ray and-ray count rates indicates that fast submillimeter pulses are the signatures of primary energetic injections. The characteristics of the fast spikes at 212 and 405 GHz, such as their flux density and localization, compared to those of the underlying slower impulsive component, also suggest that their nature is different.

A New Solar Burst Spectral Component Emitting Only in the Terahertz Range

“…The rapid subsecond pulses at 212 and 405 GHz, within the 10 s time sample shown in Figures 2 (bottom) and 3, present some of the properties found for other events reported recently (Kaufmann 2002;Raulin et al 2003). A positive spectral index for their flux in excess of the bulk emission is shown in Figure 4.…”

“…Two other beams are nearly 8Ј away from the central cluster, pointing to the solar disk, and do not need to be considered here. The first results obtained with the new instrument revealed rapid subsecond pulses for all events analyzed, for which the burst bulk emissions levels were part of the well-known microwave spectrum, exhibiting spectral intensities reducing for higher frequencies, sometimes lower than the sensitivity limits (Kaufmann 2002;Raulin et al 2003). The submillimeter-wavelength pulses' occurrence rates and amplitudes were found to follow approximately the time profiles of fluxes of bulk emission-when the latter were observed above the sensitivity limit-and at hard X-ray and gamma-ray energy ranges (Kaufmann 2002;Raulin et al 2003).…”

“…Their positions are quite concentrated with respect to the bulk positions, scattered by less than about 12Љ rms. The timescales of the individual pulses are typically 500-700 ms, longer than the 100-500 ms found before (Kaufmann 2002;Raulin et al 2003). The rapid pulses might be directly counted in a digital oscilloscope, for example.…”

Evidence that Synchrotron Emission from Nonthermal Electrons Produces the Increasing Submillimeter Spectral Component in Solar Flares

“…Intense submillimeter pulses lasting less than a second were also observed in this flare, similar to what was observed in other large flares (Raulin et al, 2003). Figure 3 displays time profiles of the 212-and 405-GHz emissions for five intervals between the dashed lines in Figure 2.…”

“…Most of these flares exhibit subsecond pulses in the >200 GHz emission (Raulin et al, 2003). These flare observations revealed a new phenomenon: When simultaneous data at lower radio frequencies are also available, two different types of spectral behavior are observed.…”