Broadband Quasi‐periodic Radio and X‐Ray Pulsations in a Solar Flare

Abstract

We describe microwave and hard X-ray observations of strong quasi-periodic pulsations from the GOES X1.3 solar flare on 2003 June 15. The radio observations were made jointly by the Owens Valley Solar Array (OVSA), the Nobeyama Polarimeter (NoRP), and the Nobeyama Radioheliograph (NoRH ). Hard X-ray observations were made by RHESSI. Using Fourier analysis, we study the frequency-and energy-dependent oscillation periods, differential phase, and modulation amplitudes of the radio and X-ray pulsations. Focusing on the more complete radio observations, we also examine the modulation of the degree of circular polarization and of the radio spectral index. The observed properties of the oscillations are compared with those derived from two simple models for the radio emission. In particular, we explicitly fit the observed modulation amplitude data to the two competing models. The first model considers the effects of MHD oscillations on the radio emission. The second model considers the quasiperiodic injection of fast electrons. We demonstrate that quasi-periodic acceleration and injection of fast electrons is the more likely cause of the quasi-periodic oscillations observed in the radio and hard X-ray emission, which has important implications for particle acceleration and transport in the flaring sources.

Modeling of Gyrosynchrotron Radio Emission Pulsations Produced by Magnetohydrodynamic Loop Oscillations in Solar Flares

“…We start from the sausage mode oscillations of a radio source with default-value parameters where the radio spectrum peak (see Figure 1(c)) is formed by the optical thickness effect like in Fleishman et al (2008), while the Razin-effect is unimportant. Figure 2 displays the oscillating components of the radio emission at three characteristic frequencies selected in the optically thick, spectrum peak, and optically thin regions of the spectrum, respectively.…”

“…Furthermore, different peaks may be the results of different physical processes, or of different modes of MHD oscillations, and a quantitative analysis of partial modulation can help discern these different causes. The partial modulation amplitude m p (f ) of radiation from a limited region of Fourier harmonics from n 1 to n 2 covering each main Fourier peak is defined as follows (Fleishman et al 2008):…”

“…Typically, these QPPs have rapidly varying amplitudes, variable periods, and narrow bandwidths δf/f 1 (e.g., Young et al 1961;Zlobec et al 1987;Stepanov & Yurovsky 1990;Kurths et al 1991;Yurovsky 1991;Fleishman et al 1994;Aschwanden et al 1995;Fleishman et al 2002aFleishman et al , 2002bMagdalenić et al 2002;Benz et al 2005;Mészárosová et al 2005;Chen & Yan 2007;Benz et al 2011;Chen et al 2011). Longer-period QPPs, with periods τ 10 s, are observed in microwaves; such QPPs are often accompanied by QPPs in hard X-rays (HXRs; e.g., Parks & Winckler 1969;Janssens et al 1973;Zaitsev & Stepanov 1982a;Kane et al 1983;Nakajima et al 1983;Asai et al 2001;Grechnev et al 2003;Nakariakov et al 2003;Stepanov et al 2004;Melnikov et al 2005;Fleishman et al 2008). …”

“…Numerous models have been proposed to account for the various types of oscillations, QPPs, and related phenomena observed at radio wavelengths (e.g., Aschwanden 1987;Nakariakov et al 2003;Fleishman et al 2008, and references therein). Generally speaking, for radio emissions produced by coherent radiation processes (such as fast millisecond pulsations), QPPs are believed to result from nonlinear, self-organizing wave-wave or wave-particle interactions (Zaitsev & Stepanov 1975;Meerson et al 1978;Bardakov & Stepanov 1979;Aschwanden & Benz 1988;Fleishman et al 1994;Korsakov & Fleishman 1998).…”

Intensity variations associated with fast sausage modes

“…However, as pointed out in Cooper et al (2003a), the manifestation of MHD modes in observations in the optically thin regime is also significantly affected by the effects of the line-of-sight (LOS) integration namely the change in the column depth of the waveguide, along the LOS, by the mode. In particular, the importance of this effect for the sausage mode arguably observed in the modulation of gyrosynchrotron emission, was pointed out by Fleishman et al (2008). We consider the role of the LOS-integration effect for the thermal emission.…”