co-spatial white light and hard x-ray flare footpoints seen above the solar limb: rhessi and hmi...
Post on 26-Dec-2015
219 Views
Preview:
TRANSCRIPT
Co-spatial White Light and Hard X-ray Flare Footpoints seen above the Solar Limb:
RHESSI and HMI observations
Säm KruckerSpace Sciences Laboratory, UC Berkeley
University of Applied Sciences Northwestern Switzerland
Implications for flare energetics and chromospheric evaporation
HXR bremsstrahlung
• Flare loop T, V, n
• Spectrum of acc. electrons
thermal bremsstrahlung
T ~ 30 MK
non-thermal bremsstrahlungaccelerated electrons with typical energies
above ~10 keV
Flare footpoints in WL and HXR
Carrington, R. C., 1859
Close connection in space, time, and intensity.
2 arcsec
Flare ribbons in WL and HXR
Carrington, R. C., 1859
Close connection in space, time, and intensity.
25-100 keVSOT G-band
2 arcsec
Krucker et al. 2011
Heating of flare ribbons
SDO/HMI(6173 A)
Significant fraction of flare energy is radiated away in optical range
SDO/AIA 171 A(~1 MK)
Flares larger than GOES M5 can be generally detected with HMI, for smaller events non-flare related time variations are hiding flare mission.
(Kuhar et al. 2015, TBS)
HM
I 61
73 A
incr
ease
RHESSI 30 keV flux
Statistical study HMI/RHESSI: all flares have WL footpoints
Good correlation strongly suggests that flare-accelerated electrons are involved in
the production of the WL emission
Kyoko Watanabe et al. 2010
Assuming:thick target (HXR)black body (WL)
E0=low energy cutoff in electron spectrum
40-100 keVSOT G-band
IRIS continuum observations from flare ribbon (GOES X1)
Heinzel & Kleint 2014Kleint et al. 2015 (to be submitted)
IRIS continuum
RHESSI30-100 keV
IRIS, HMI, FIRS continuum
HMI
FIRSIRIS
Kleint et al. 2015 (to be submitted)
Energy in >27 keV is equal to radiative losses in optical range
First attempt: Thick target modelAbbett et al. 2015 (to be submitted)
Next step: compare to modeling
Heating of flare ribbons to ~MK
SDO/AIA 171 A(~1 MK)
Heated ribbon can evaporate hot plasma into corona to form flare loopThermal conduction from hot coronal loop can also drive evaporation
De-saturated AIA 171A(Schwartz et al. 2014)
Heating of flare ribbons to ~MK
SDO/AIA 171 A(~1 MK)
Hot ribbons, but colder than post flare loops. XRT to constrain higher temperatures?
Where do flare accelerated electrons heat the chromosphere?
Thick target beam model gives altitudes of HXR source of ~800-3000 km (see Battaglia et al. 2012):
• Density • Energy of electrons• Pitch angle• Ionization level• Field line tilt
Since these parameters are mostly unknown, there is no unique prediction.
photosphere
flare-acceleratedelectrons
HXR source in chromosphere due to bremsstrahlung
Range for low density models800 – 1500 km
Stereoscopic observations
photosphere
flare-acceleratedelectrons
HXR source in chromosphere due to bremsstrahlung
Range for low density models800 – 1500 km
Martinez-Oliveros et al. 2012:RHESSI/HMI/STEREO• Use STEREO EUV ribbon
as proxy• Single event
Absolute source height at 305+-170 km195+-70 km
This is surprisingly low:•Very, very low density•Source within Wilson depression•Not thick target beam model
indirectly observed
Stereoscopic observations
photosphere
flare-acceleratedelectrons
HXR source in chromosphere due to bremsstrahlung
800 – 1500 km
Martinez-Oliveros et al. 2012:RHESSI/HMI/STEREO• Use STEREO EUV ribbon
as proxy• Single event
Absolute source height at 305+-170 km195+-70 km
This is surprisingly low:•Very, very low density•Source within Wilson depression•Not thick target beam model
Altitude of WL source?Optical emission is thought to be thermal emission at low temperatures (~10 000 K)
•Heated by electrons: co-spatial source with HXRs•Backwarming would predict a lower altitude.
This talk: look at flares that occur within one degree of limb passage (Krucker et al. 2015).
HMI (617.3 nm):•resolution: 1.1”•placing: <0.1”
RHESSI hard X-rays:•resolution: 2.3”•placing: <0.1”
photosphere
flare-acceleratedelectrons
HXR source in chromosphere due to bremsstrahlung
Range for low density models800 – 1500 km
?
?
Emission from the limb is influenced by the opacity of the atmosphere
radiation cannot escape
disk
~350 km
STEREO is used to get flare location relative to limb
Projection effects estimated to be less than 100 km for derived altitudes for selected events.
Image+Image+
Co-spatial HXR and WL footpoints
Image: HMI with pre-flare image subtracted. Black is enhanced emission.30-80 keV
617.3 nm
thermal loop top
footpoints
Non-thermalabove the loop top
Image+Image+
Co-spatial HXR and WL footpoints
Altitude above photosphere:WL: 810+-70 kmHXR: 722+-122 kmLow values for TTBM
30-80 keV617.3 nm
footpoint
flare
pre-flarepre-flare derivative pre-flare
Time evolution of fluxes and altitudes
617.3 nm
30-80 keV
GOES
617.3 nm
30-80 keV
Consistent results: co-spatial emission below ~1000 km
Implications of co-spatial sources• HXR emission comes from
relative cold plasma• HXR producing electrons (>30
keV) do not heat chromosphere to millions of degrees
• Energy of >30 keV electrons are lost by radiation in the optical range
• >30 keV electrons are not responsible for evaporation!
• Heating to MK by low energy electrons at higher altitudes?
electron energy
flux
>30 keV
energy is lost to WL radiation
lower energies?
energy goes into evaporated plasma?
observation of footpoints at lower energies (<20 keV) very difficult due to limited dynamic range of RHESSI.
Low-energy (thermal) emission from footpoints is lost in limited dynamic range
Upper limits of footpoint emission at low-energies
Spectra of footpoint as inferred from images
?
Low-energy (thermal) emission from footpoints is lost in limited dynamic range
Upper limits of footpoint emission at low-energies
Spectra of footpoint as inferred from images
?HXR focusing optics can overcome this limitation
HINODE XRT and SOT observations
•XRT hot filters: – constrain high temperatures in footpoints– Time evolution: conduction vs beam heating– Locate GOES fast time variations– is a 2 second cadence to match GOES feasible, at
least for some time intervals during the flare?
•SOT– Fast time cadence to observe decay on second
time scale– Is ~2 second cadence possible in a single filter?
HINODE SOT RGB •Small source sizes•Footpoint motion?•fast decay
mismatch between spatial and time resolution
Proposition to occasionally run flare mode with higher time cadence, maybe only one filter. Summing over pixel to save telemetry.
t=0 t=19 s
t=3 s t=22 s
t=6 s t=25 s
Summary• HXR source altitude is low
<1000 km– TTBM works only with very low
density models, strongly beamed case
• Co-spatial WL and HXR sources: – energy of >30 keV electrons is
radiated in optical range
– >30 keV electrons are not responsible for evaporation!
• Unexpected results with implication on our standard picture
photosphere
flare-acceleratedelectrons
Co-spatial HXR and WL sources
<1000 Mm
Additional source?
top related