| Presentation Title: | Examining the Driver of High Contrast Lyman-alpha Emission in Solar Flares using Spectroscopic Observations from RHESSI and Fermi. |
| Author(s): | H. J. Greatorex, R. O. Milligan, and P. J. A. Simões |
Abstract:
Recent advances in observing capabilities mean that we are now more capable than ever to regularly observe flare-related Lyman-alpha (Lyα; 1216 Å) emission. However, there are still a number of unanswered questions surrounding the energy transport processes associated with the emission of this significantly intense line. Milligan et al. (2020) found that ~95% of M and X-class flares had an associated Lyα contrast of <10%, however contrasts of >10% were in fact possible with some unique cases achieving contrasts of 25-30%. The physical explanation for these uniquely high contrasts is not yet fully understood. Greatorex et al. (2023) found that nonthermal electron parameters, namely the spectral index, may be linked to the associated Lyα contrast seen in solar flares independent of their GOES magnitude. Here, we postulate that the properties of the nonthermal electron distribution may also explain the uniquely high Lyα contrasts found for some flares. To examine this, a sample of 15 flares from Solar Cycle 24 were employed, each with an associated Lyα contrast of >10%. For each flare, Hard X-Ray data from RHESSI and/or Fermi were used to derive the properties of the nonthermal electrons at the peak of the Lyα emission. Where co-observations from RHESSI and Fermi are available for a single flare, we attempt to find a scaling relationship between these observations such that a more accurate comparison can be made between flares independent of the observing instrument. It is hoped that a unique set of parameters can be discerned that drive uniquely high contrasts in Lyα emission, which may in future be validated with Radiative-Hydrodynamic flare simulations. Ultimately, this will advance our understanding of energy transport processes during solar flares and the interpretation of data from current and upcoming missions with Lyα observing capability.