Solar flare gamma rays do tend to increase during solar maximum, but the relationship is complex and influenced by several factors related to solar activity and particle acceleration processes.
Solar flares are intense bursts of radiation caused by the sudden release of magnetic energy stored in the Sun’s atmosphere. These flares emit energy across the electromagnetic spectrum, including gamma rays, which are the highest-energy form of light. Gamma rays from solar flares are produced primarily when accelerated protons and ions collide with the solar atmosphere, creating secondary particles that decay and emit gamma radiation.
During the solar cycle, which lasts about 11 years, the Sun goes through periods of minimum and maximum activity. Solar maximum is characterized by a higher number of sunspots, more frequent and intense solar flares, and increased solar energetic particle events. Because solar flares are more frequent and often more powerful during solar maximum, the overall gamma-ray emission from the Sun tends to increase during these times.
Observations from instruments like the Fermi Large Area Telescope (Fermi-LAT) have cataloged dozens of solar flares emitting gamma rays in the energy range from tens of MeV (million electron volts) up to several GeV (billion electron volts). These observations show that solar flares detected in gamma rays are often associated with active regions on the Sun, which are more numerous and dynamic during solar maximum. Some gamma-ray flares have even been detected from regions just beyond the visible edge of the Sun, indicating complex magnetic and particle acceleration processes at work.
The gamma-ray emission from solar flares is not just a simple increase in intensity but also involves changes in the particle acceleration mechanisms. While typical solar flares emit mainly electrons, the gamma-ray flares detected at higher energies suggest significant acceleration of protons and heavier ions. These particles interact with the solar atmosphere to produce gamma rays through processes such as pion decay, which is a signature of hadronic interactions.
Moreover, the intensity and timing of gamma-ray emission can vary widely from flare to flare. Some flares produce impulsive gamma-ray bursts that rise and fall quickly, while others show gradual, long-lasting gamma-ray emission. This variability is influenced by the magnetic connectivity between the flare site and the observer, as well as the presence of coronal mass ejections (CMEs) that can drive shock waves accelerating particles over extended periods.
In addition to solar flares themselves, cosmic rays impacting the Sun can also produce gamma rays through interactions with the solar atmosphere. This background gamma-ray emission varies with the solar cycle because the solar magnetic field modulates the cosmic ray flux reaching the Sun. During solar maximum, the stronger solar magnetic field reduces the cosmic ray flux near the Sun, which can affect the baseline gamma-ray emission unrelated to flares.
In summary, solar flare gamma rays generally increase during solar maximum due to the higher frequency and intensity of flares and enhanced particle acceleration in active regions. However, the detailed gamma-ray emission depends on the complex interplay of magnetic activity, particle acceleration mechanisms, flare location, and cosmic ray modulation. Observations over multiple solar cycles continue to improve our understanding of these processes, revealing a dynamic and intricate gamma-ray sky centered on our nearest star.