Active region emission measure distributions and implications for nanoflare heating
- Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London SW7 2BW, UKAND (United Kingdom)
- (United Kingdom)
The temperature dependence of the emission measure (EM) in the core of active regions coronal loops is an important diagnostic of heating processes. Observations indicate that EM(T) ∼ T{sup a} below approximately 4 MK, with 2 < a < 5. Zero-dimensional hydrodynamic simulations of nanoflare trains are used to demonstrate the dependence of a on the time between individual nanoflares (T{sub N} ) and the distribution of nanoflare energies. If T{sub N} is greater than a few thousand seconds, a < 3. For smaller values, trains of equally spaced nanoflares cannot account for the observed range of a if the distribution of nanoflare energies is either constant, randomly distributed, or a power law. Power law distributions where there is a delay between consecutive nanoflares proportional to the energy of the second nanoflare do lead to the observed range of a. However, T{sub N} must then be of the order of hundreds to no more than a few thousand seconds. If a nanoflare leads to the relaxation of a stressed coronal field to a near-potential state, the time taken to build up the required magnetic energy is thus too long to account for the EM measurements. Instead, it is suggested that a nanoflare involves the relaxation from one stressed coronal state to another, dissipating only a small fraction of the available magnetic energy. A consequence is that nanoflare energies may be smaller than previously envisioned.
- OSTI ID:
- 22351490
- Journal Information:
- Astrophysical Journal, Vol. 784, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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