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

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

3. Normal spectrum: average plage

4. 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 !!

5. 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 Å Si IV 1403.77 O IV 1400 O IV 1401 from C HIANTI

6. 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

7. 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

8. 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; Dudík 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

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

10. 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

11. 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)

12. thanks…

13. Line list

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