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 that 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) on board 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's 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 the FIP. The abundances are almost constant during the flares, with the exception of Si which increases by a factor of ∼2 in the decay phase. The evolution of the Si abundance is consistent with the finding that the I-FIP plasma originates from chromospheric evaporation and then mixes with the surrounding low-FIP biased materials. Flare-to-flare abundance varied by a factor of two, agreeing with past observations of solar flares. Finally, we emphasize that Earth albedo data acquired by X-ray astronomy satellites like Suzaku and the X-Ray Imaging Spectroscopy Mission can significantly contribute to studies of solar physics.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2020
- DOI:
- 10.3847/1538-4357/ab7207
- arXiv:
- arXiv:2001.10643
- Bibcode:
- 2020ApJ...891..126K
- Keywords:
-
- Solar abundances;
- Solar flares;
- Solar corona;
- Solar x-ray emission;
- Solar x-ray flares;
- 1474;
- 1496;
- 1483;
- 1536;
- 1816;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 19 pages, 10 figures, accepted for publication in The Astrophysical Journal