High Energies in the Inner Heliosphere
| Nugget | |
|---|---|
| Number: | 258 |
| 1st Author: | Hugh Hudson |
| 2nd Author: | |
| Published: | 24 August 2015 |
| Next Nugget: | |
| Previous Nugget: | A Failed Eruption with a Two-Ribbon Flare |
Introduction
How bright is the hard X-ray Sun at solar minimum? We do not know, since even RHESSI has only established upper limits at present (Ref. [1]). Why should it emit any hard X-rays at all? This is easy to answer, at least partially, and there are observations by Fermi at much higher photon energies (Ref. [2]) - indeed, Fermi observes not only the disk of the Sun, but also a diffuse source centered on it. Both of these components originate in galactic cosmic rays with energies high enough to penetrate into the inner heliosphere, and even to strike and interact in the photosphere itself. This would be the solar equivalent, not much explored yet, of the celebrated Størmer problem of cosmic-ray transport around the Earth.
There are other processes in which the heliosphere plays a role in the hard X-ray and gamma-ray emission from quiet Sun. This Nugget lists a few phenomena related to high-energy particles in the inner heliosphere (please also see the recent Nugget on flare-related particles, neutrons, and gamma-rays.
Processes
Items of interest include some of the following, which we hope to explore in future Nuggets.
- Nanoflares (our upper-limits Nugget
- Cosmic-ray impacts (the [Fermi disk source]; see this
- Cosmic-ray electrons (an [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Scattered_Light:_Inverse_Compton_Scattering_and_Coronal_Hard_X-ray_Sources earli
er Nugget])
- Cosmic-ray shadows (described below)
- Flare-associated neutral atoms (Ref. [3])
- "Solar cosmic rays" and neutrons (particles, neutrons, and gamma-rays)
- Long-duration gamma-ray events (An earlier Nugget, and
more to come)
References
[1] "Constraining the Hard X-ray Properties of the Quiet Sun with New RHESSI Observations"