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
Emerging AR (24. Sep. 2013): IRIS & SDO
Si IV spectroheliogram
AIA 171 Å
these events happen
at places of flux cancellation
IRIS 1400 Å
HMI Blos
70” x 35”
AIA 304 Å
three bright features
with lifetimes of > 5 min
AIA 1600 Å
Normal spectrum: average plage
Strange spectra: in a bomb
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
Density diagnostics
O IV 1400
O IV 1401
traditional density diagnostics:
ratio of forbidden lines
spectral radiance [DN / pixel]
with IRIS:
O IV lines around 1400 Å
O IV
1401.16
O IV
1399.77
Si IV
1403.77
Doppler shift relative to target line rest wavelength [km/s]
O IV 1400
≈ 0.26 → ne ≈ 4 x 1010 cm-3
O IV 1401
from CHIANTI
Density diagnostics in bombs: lower limit
spectral radiance [DN / pixel]
O IV
1401.16
O IV
1401.16
O IV
1399.77
Si IV
1403.77
Si IV
1403.77
Doppler shift relative to target line rest wavelength [km/s]
no O IV lines
upper limit:
Si IV 1394
> 700
O IV 1401
Si IV 1394
≈ 10
O IV 1401
spectral radiance [DN / pixel]
Density diagnostics in bombs: lower limit
O IV
1401.16
no O IV lines
upper limit:
Si IV
1403.77
Si IV 1394
> 700
O IV 1401
→ density
@ Si IV origin: >5 x 1013 cm-3
Doppler shift relative to target line rest wavelength [km/s]
@ Mg II origin: >3 x 1014 cm-3
→ comparable to density
at T mimimum
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
Scenario for the bombs
similar to EB scenario 1 in
Georgoulis et al (2002) ApJ 575, 506
Relation to Ellerman bombs ?
► unclear from observations, so far…
– no H-a Ellerman bombs found
at locations of these strange Si IV profiles
Si IV
(ongoing work,
Vissers, G., Rouppe van der Voort et al, poster 4.21)
► 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: ~ 1028 ergs
(Georgoulis et al. 2002; ApJ 575, 506)
Si IV bombs:
~ 1029 ergs ~10 x EB
Si IV bomb
EB
QS
Ellerman bomb H-a
Yang et al. (2013) Sol. Phys. 288, 39
► some of the Si IV bombs show
also coronal counterpart
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 explosions
in the cool solar atmosphere
thanks…
Line list
O IV lines and kappa-distributions
Dudík et al (2014, ApJ 780, L12)