Journal
ASTROPHYSICAL JOURNAL
Volume 856, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/1538-4357/aab49e
Keywords
line: profiles; Sun: activity; Sun: corona; Sun: transition region
Categories
Funding
- NASA grant [NNX15AF50G, NNX15AF47G, NNM07AB07C]
- Lockheed-Martin [8100002705]
- IRIS [NNG09FA40C]
- Research Council of Norway through its Centres of Excellence scheme [262622]
- NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center
- ESA
- Norwegian Space Centre
- International Space Science Institute (ISSI)
- Research Council of Norway
- NASA [NNX15AF47G, 805310, NNX15AF50G, 804059] Funding Source: Federal RePORTER
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We present the results of 1D hydrodynamic simulations of coronal loops that are subject to nanoflares, caused by either in situ thermal heating or nonthermal electron (NTE) beams. The synthesized intensity and Doppler shifts can be directly compared with Interface Region Imaging Spectrograph (IRIS) and Atmospheric Imaging Assembly (AIA) observations of rapid variability in the transition region (TR) of coronal loops, associated with transient coronal heating. We find that NTEs with high enough low-energy cutoff (E-C) deposit energy in the lower TR and chromosphere, causing blueshifts (up to similar to 20 km s(-1)) in the IRIS Si IV lines, which thermal conduction cannot reproduce. The E-C threshold value for the blueshifts depends on the total energy of the events (approximate to 5 keV for 10(24) erg, up to 15 keV for 10(25) erg). The observed footpoint emission intensity and flows, combined with the simulations, can provide constraints on both the energy of the heating event and Ec. The response of the loop plasma to nanoflares depends crucially on the electron density: significant Si IV intensity enhancements and flows are observed only for initially low-density loops (<10(9) cm(-3)). This provides a possible explanation of the relative scarcity of observations of significant moss variability. While the TR response to single heating episodes can be clearly observed, the predicted coronal emission (AIA 94 angstrom) for single strands is below current detectability and can only be observed when several strands are heated closely in time. Finally, we show that the analysis of the IRIS Mg II chromospheric lines can help further constrain the properties of the heating mechanisms.
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