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Microwave and Hard X-Ray Spectral Evolution for the 13 December 2006 Solar Flare

“…The microwave spectral index is harder than the hard X-ray index during this event, which is consistent with previous findings (e.g. White and Kundu, 1992;Kundu et al, 1994;Silva et al, 1997;Raulin et al, 1999;Silva, 1999, 2000). All the subpeaks follow the soft-hardsoft spectral behaviour in the hard X-ray rise-peak-decay phases.…”

“…The hard X-ray presents a SHS pattern, while the microwave should show a SHH pattern. This result is consistent with previous findings for some individual flares (e.g., White and Kundu, 1992;Kundu et al, 1994;Silva et al, 1997;Silva, Wang, and Gary, 2000;Raulin et al, 1999;Silva, 1999, 2000). However, it seems that the microwave emission shows a hard-soft-hard pattern over the timescale of soft-hard-soft hard X-rays.…”

“…Based on Nobeyama Radio Polarimeters (NoRP; Nakajima et al, 1985) observations during cycle 23, Ning and Ding (2007) statistically studied the microwave spectral evolution in 103 solar flares, and found that the gradualhard events (91 out of their samples) dominate in the microwave emission. This is consistent with previous results from data obtained by the Burst and Transient Source Experiment (BATSE) and the Owens Valley Radio Observatory (OVRO) (Marsh et al, 1981;Alissandrakis, 1986;Nitta et al, 1991;White and Kundu, 1992;Kundu et al, 1994;Silva et al, 1997;Silva, Wang, and Gary, 1999;Raulin et al, 1999;Silva, 1999, 2000). Silva (1999, 2000) found that some solar flares decrease the microwave spectral index but simultaneously increase the hard X-ray spectral index during the decay phase.…”

Multiple Components in the Millimeter Emission of a Solar Flare

“…However those observations refer to large ares, unlike the event presented in this paper (GOES class B5.6). In other studies including also small ares, it has been inferred that the high-energy electron distribution di ers from the low-energy distribution (Alissandrakis 1986, Staehli, Gary & Hurford 1989, Lim et al 1992, Kundu et al 1994, Silva et al 1997. In some previous studies there had been ambiguity regarding the radio spectral index because of uncertainty in the spectral peak frequency: in this paper, as in Silva et al (1996a), the use of OVRO data allows us to determine the turnover frequency peak unambigously, and its value of 6.5 GHz (typical for small ares) ensures that the 17 GHz and the 86 GHz emissions are optically thin, and they are then directly related to the energy distribution of the energetic emitting electrons.…”

“…A con dent determination of both hard X-ray and radio spectral indices is necessary in order to determine whether hard X-ray and radio emissions come from the same population of accelerated electrons. In a number of observations it has been inferred that the energy distribution of millimeter{emitting electrons is harder than that of the electrons producing hard X-rays and microwaves in the same ares (Kundu et al 1994, Silva et al 1997). Occasionally ares have been observed { 3 { to show breaks in their hard X{ray spectra such that the higher{energy electrons have a harder spectrum (Dennis 1985, Vilmer 1997.…”