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Hot explosions in the cool solar atmosphere Hardi Peter Max Planck Institute for Solar System Research Gttingen H. Tian, W. Curdt, D. Schmit, D. Innes, B. De Pontieu, & IRIS team

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Emerging AR (24. Sep. 2013) : IRIS & SDO three bright features with lifetimes of > 5 min Si IV spectroheliogram IRIS 1400 AIA 171 AIA 304 AIA 1600 HMI B los 70 x 35 these events happen at places of flux cancellation

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Normal spectrum: average plage

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Strange spectra: in a bomb absorption lines ! ~5 km/s blueshift absorption lines ! ~5 km/s blueshift missing O IV lines optically thin bi-directional flow same profile envelope in Mg II, C II, Si IV !! same profile envelope in Mg II, C II, Si IV !!

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Density diagnostics Doppler shift relative to target line rest wavelength [km/s]spectral radiance [DN / pixel] O IV 1399.77 O IV 1401.16 O IV 1400 O IV 1401 0.26 n e 4 x 10 10 cm -3 traditional density diagnostics: ratio of forbidden lines with IRIS: O IV lines around 1400 Si IV 1403.77 O IV 1400 O IV 1401 from C HIANTI

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Density diagnostics in bombs: lower limit Doppler shift relative to target line rest wavelength [km/s]spectral radiance [DN / pixel] O IV 1399.77 O IV 1401.16 Si IV 1403.77 Si IV 1394 O IV 1401 10 no O IV lines upper limit: Si IV 1394 O IV 1401 > 700 O IV 1401.16 Si IV 1403.77

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Density diagnostics in bombs: lower limit Doppler shift relative to target line rest wavelength [km/s] spectral radiance [DN / pixel] O IV 1401.16 Si IV 1403.77 Si IV 1394 O IV 1401 > 700 no O IV lines upper limit: density @ Si IV origin: >5 x 10 13 cm -3 @ Mg II origin: >3 x 10 14 cm -3 comparable to density at T mimimum density @ Si IV origin: >5 x 10 13 cm -3 @ Mg II origin: >3 x 10 14 cm -3 comparable to density at T mimimum

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Summary of observations absorption lines (!) in EUV these line of neutral or singly ionized species have blueshifts of ~5 km/s cool layer above energy deposition event still optically thin in Si IV bi-modal profile of Si IV (and C II, Mg II) strong bi-directional flow (supersonic, ~ Alfven-speed) similar envelope of line profile in Mg II, C II, Si IV multi-thermal flow hosting plasma over a wide T range flux cancellation below brightenings reconnection (consistent with flow speeds) no O IV forbidden line emission with other evidence: source region in high-density plasma (probably not effect of non-Maxwellian e distribution; Dudik et al. 2014, ApJ 780, L12) weak ( / no) signature in 171 and 304 bands overlying cool layer absorbs in He I and He II Lyman continua

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Scenario for the bombs similar to EB scenario 1 in Georgoulis et al (2002) ApJ 575, 506

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Relation to Ellerman bombs ? Ellerman bomb H- unclear from observations, so far no H- Ellerman bombs found at locations of these strange Si IV profiles (ongoing work, Vissers, G., Rouppe van der Voort et al, poster 4.21) some of the Si IV bombs show also coronal counterpart peaks of EB spectral profiles in H-a at different Doppler shifts than Si IV and Mg II in Si IV bombs so far no enhancement in TR emission reported for EBs energy estimations: Ellerman bombs: ~ 10 28 ergs (Georgoulis et al. 2002; ApJ 575, 506) Si IV bombs: ~ 10 29 ergs ~10 x EB Yang et al. (2013) Sol. Phys. 288, 39 Si IV bomb Si IV QS EB

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Conclusions Hot explosions in the cool solar atmosphere highlights importance of high spectral resolution (otherwise the absorption lines would not be visible) energy release deep in the atmosphere (near/below T minimum) overlying chromosphere is pushed upwards huge amount of energy required to power flows and heat plasma how is the chromospheric plasma heated to 100.000 K or even more? 3D MHD models predict only modest T increase (e.g. Archontis & Hood, 2009; A&A 508, 1469)

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thanks

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Line list

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O IV lines and kappa-distributions Dudk et al (2014, ApJ 780, L12)