NuSTAR Observation of a Minuscule Microflare in a Solar Active Region

Area of Science:

• Solar Physics
• Plasma Astrophysics
• X-ray Astronomy

Background:

• Solar flares are sudden bursts of energy from the Sun's surface.
• Microflares are smaller-scale solar flare events.
• Understanding microflares provides insights into energy release mechanisms in solar active regions.

Purpose of the Study:

• To perform X-ray imaging spectroscopy of an extremely weak solar active region (AR) microflare.
• To characterize the thermal properties and energy of this microflare.
• To determine upper limits for non-thermal emission in such weak events.

Main Methods:

• Utilized data from the Nuclear Spectroscopic Telescope Array (NuSTAR) for X-ray observations (2.5-7 keV).
• Employed the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) for analysis of Fe XVIII emission (94 Å channel).
• Estimated thermal energy, temperature, and emission measure of the microflare.

Main Results:

• Observed one of the weakest AR microflares ever studied, with an energy approximately three orders of magnitude lower than a GOES A-class microflare (1.1 × 10^26 erg).
• Determined a peak temperature of 6.7 MK and an emission measure of 8.0 × 10^43 cm^-3.
• Found no detectable non-thermal emission, establishing upper limits for such emission.

Conclusions:

• The study presents the lowest thermal energy estimate for an AR microflare in existing literature.
• This microflare operates at the lower boundary of what is classified as an X-ray microflare.
• The findings contribute to understanding the energy scales and characteristics of the weakest solar flare events.