Energetics of chromospheric flares: Continuum radiation

P. Heinzel

Solar  white-­‐light  flare  (WLF)  

Mauas+ 1991

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The solar VUV spectrum

Milligan+ 2014

about 15% of the total non-thermal energy radiated in these lines and continuum channels

Two types of WLFs

Hydrogen free-bound recombination continuum (e.g. Balmer) enhancement (chromosphere)

Visible-continuum enhancement due to H-minus

opacity (photosphere)

Ricchiazzi & Canfield (1983) static models (5,09,0) (5,10,0) (5,11,0)

Ground-based detection (see P. Kotrc’s talk)

SDO/EVE

Ground-based detection

IRIS NUV channel

color-coded positions along slit for other plots

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date_obs: 2014-03-29T17:47:19.690

IRIS NUV spectra

Heinzel & Kleint (2014)

2014-03-29T17:47:19.690

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y= 423, max redshifty= 447, bright continuumy= 468, bright upper stripy= 620, QSy= 314, bright outside flare

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IRIS SJI 1400 29-Mar-2014 17:47:36.683 UT

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orange: jumps in continuum counts > 30 DN/s at ~17:47 - avg(17:40-17:44)pink: RHESSI [50,70,90]% HXR contours at 17:47:20

Lightcurve y= 423

17:32 17:36 17:40 17:44 17:48 17:52Start Time (29-Mar-14 17:28:36)

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Lightcurve y= 447

17:32 17:36 17:40 17:44 17:48 17:52Start Time (29-Mar-14 17:28:36)

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Lightcurve y= 468

17:32 17:36 17:40 17:44 17:48 17:52Start Time (29-Mar-14 17:28:36)

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Lightcurve y= 620

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Lightcurve y= 314

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2014-03-29T17:47:19.690

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Balmer-continuum light curves

Kleint+ 2015 (ApJ submitted)

Kleint+ 2015 Heinzel & Kasparova 2015

Flare radiative output in the continuum:

Kleint+ 2015 - Balmer continuum added and backwarming tested for X-class flare of 29 March 2014

Balmer-continuum radiation losses – 3.8 1010 erg s-1 cm-2

fits the IRIS data

WL radiation losses (FLA model) - 2.4 1010 erg s-1 cm-2

electron-beam energy deposit (RHESSI) - 3.5 1011 erg s-1 cm-2

about 10 % of deposited energy is radiated in the continua

some energy radiated away in spectral lines

rougly 80 – 90 % goes into heating and dynamics

Set of 1D plane-parallel equations of RHD Flarix code

non-thermal coll. rates non-equilibrium hydrogen ionization

beam heating Q

Kasparova+ 2009 Varady+ 2010

Model H_TP_D3 1D flare loop photosphere-corona initial atmosphere – VAL3C electron-beam flux – trapezoidal profile F20 = 4.5 × 1010 erg s-1 cm-2 spectral index δ = 3 Etot = 9 × 1010 erg cm-2

Synthetic BC light curve for model H_TP_D3

constrained by IRIS NUV spectra

Summary

§  RHD time variations of the Balmer-continuum emission are consistent with IRIS-NUV light curves

§  Slow non-equilibrium hydrogen recombination is well reflected in BC light curves

§  For a short trapezoidal electron-beam pulse the synthetic intensity is a factor of five lower than IRIS spectra from an X-class flare

§  A series of beam pulses should lead to a stronger Balmer continuum more consistent with the IRIS spectra

§  Radiative cooling is dominated by Balmer and Paschen continuum => significant amount of deposited energy is radiated away in subordinate continua

The   research   leading   to   these   results   has  received   funding   from   the   European  Community's   Seventh   Framework   Programme  (FP7/2007-­‐2013)   under   grant   agreement   no.  606862  (F-­‐CHROMA)