Inverse First Ionization Potential Effects in Giant Solar Flares Found from Earth X-Ray Albedo with Suzaku/XIS

Abstract

We report X-ray spectroscopic results for four giant solar flares occurred on 2005 September 7 (X17.0), 2005 September 8 (X5.4), 2005 September 9 (X6.2), and 2006 December 5 (X9.0), obtained from Earth albedo data with the X-ray imaging spectrometer (XIS) onboard Suzaku. The good energy resolution of the XIS (FWHM∼100 eV) enables us to separate a number of line-like features and detect the underlying continuum emission. These features include Si Heα, Si Lyα, S Heα, S Lyα, Ar Heα, and Ca Heα originating from solar flares as well as fluorescent Ar Kα and Ar Kβ from the Earth atmosphere. Absolute elemental abundances (X/H) averaged over the four flares are obtained to be ∼2.0 (Ca), ∼0.7 (Si), ∼0.3 (S), and ∼0.9 (Ar) at around flare peaks. This abundance pattern is similar to those of active stars' coronae showing inverse first ionization potential (i-FIP) effects, i.e., elemental abundances decrease with decreasing FIP with a turnover at the low end of FIP. The abundances are almost constant during the flares, with an exception of Si which increases by a factor of ∼2 in the decay phase. The evolution of the Si abundance is consistent with a picture that the i-FIP plasma originates from the chromosphere evaporation and then mixes with the surrounding low-FIP biased materials. Flare-to-flare abundance varied by a factor of 2, agreeing with past observations of solar flares. Finally, we emphasize that Earth albedo data acquired by X-ray astronomy satellites like Suzaku and XRISM can significantly contribute to studies of solar physics.

Coronal Elemental Abundance: New Results from Soft X-Ray Spectroscopy of the Sun

“…A dotted line is drawn at FIP bias value equal to 1 which is when coronal abundances equal photospheric values. The general trend for all elements of lower FIP bias for stronger flares (Figure 6), is consistent with the speculation in Katsuda et al (2020) that more intense flares show larger departures of FIP values from nominal. Katsuda et al (2020) used albedo signal from Earth's atmosphere during four giant solar flares measured using the X-ray imaging spectrometer on Suzaku.…”

The Evolution of Plasma Composition during a Solar Flare

“…Warren (2014) studied 21 M-and X-class flares using the Solar Dynamics Observatory/EUV Variability Experiment (SDO/EVE) and showed that ablation acted on all elements and turned the Sun-as-a-star coronal elemental abundances temporarily closer to photospheric, in agreement with earlier results of Veck & Parkinson (1981), Feldman & Widing (1990), McKenzie &Feldman (1992), andDel Zanna &Woods (2013). However, an explanation that only comprises of ablation falls short on addressing some observations that obtained an enhanced low-FIP elemental abundances (e.g., Doschek et al 1985;Sterling et al 1993;Bentley et al 1997;Fludra & Schmelz 1999;Phillips et al 2010;Phillips & Dennis 2012;Dennis et al 2015;Sylwester et al 2015), as well as the more recent observations that have found evidence of an inverse FIP (IFIP) effect during different phases of flares occurring in very complex active regions (Doschek et al 2015;Doschek & Warren 2016;Baker et al 2019Baker et al , 2020Katsuda et al 2020).…”

Can Subphotospheric Magnetic Reconnection Change the Elemental Composition in the Solar Corona?

“…The Sun-as-a-star (Warren 2014) and stellar (Audard et al 2003;García-Alvarez et al 2009;Testa et al 2015) observations during flares are consistent with this, since they indicate that the overall elemental composition is getting close to the photospheric value. The presence of bright I-FIP patches shifts the overall composition of FIP-effect dominated coronae even more toward photospheric or indeed to I-FIP effect values (e.g., Katsuda et al 2020).…”

“…Composition studies of stellar flares provide strong indications of a similar effect, i.e., that the elemental abundances tend to approach photospheric values both on FIP-effect and I-FIP-effect dominated stars (e.g., Nordon & Behar 2008;Laming & Hwang 2009). Recently, Katsuda et al (2020) reported the I-FIP effect in four large X-class flares (X17.0, X5.4, X6.2 from AR 10808 and X9.0 from AR 10930) derived from Earth albedo X-ray spectra from the imaging spectrometer on board the Suzaku astronomical satellite. Baker et al (2019) analyzed in detail Hinode/EIS observations of plasma composition during the decay phase of an M-class flare in AR 11429.…”