Hot explosions in the cool solar atmosphere

1. Hot explosionsin the cool solar atmosphere Hardi Peter Max PlanckInstitute 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 Si IV spectroheliogram AIA 171 Å these events happen at places of flux cancellation IRIS 1400 Å AIA 304 Å three bright features with lifetimes of > 5 min HMI Blos AIA 1600 Å 70” x 35”

3. Normal spectrum: average plage

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

5. Density diagnostics O IV 1400 O IV 1401 traditional density diagnostics: ratio of forbidden lines with IRIS: O IV lines around 1400 Å ≈ 0.26 → ne ≈ 4 x 1010 cm-3 O IV 1401.16 from Chianti Si IV 1403.77 O IV 1399.77 spectral radiance [DN / pixel] Doppler shift relative to target line rest wavelength [km/s] O IV 1400 O IV 1401

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

7. Density diagnostics in bombs: lower limit no O IV lines upper limit: Si IV 1394 O IV 1401 > 700 Si IV 1403.77 O IV 1401.16 spectral radiance [DN / pixel] → density@ Si IV origin:>5 x 1013cm-3 @ Mg II origin: >3 x 1014cm-3 → comparable to density at Tmimimum Doppler shift relative to target line rest wavelength [km/s]

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 Trange ► 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 ? ► unclear from observations, so far… – no H-aEllerman 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: ~1028ergs (Georgouliset al. 2002; ApJ 575, 506) Si IV bombs: ~ 1029ergs~10 x EB Si IV Si IV bomb EB QS Yang et al. (2013) Sol. Phys. 288, 39 Ellerman bomb H-a

11. Conclusions ► 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) Hot explosionsin the cool solar atmosphere

12. thanks…

13. Line list

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