n-distribution

Non-thermal distributions in RHESSI and RESIK spectra
J. Kašparová1, A. Kulinová1,2, E. Dzifčáková1 J. Sylwester3, B. Sylwester3 and M. Karlický1
1Astronomical Institute AS CR, v. v. i., Fričova 298, 251 65 Ondřejov, Czech Republic, [email protected]
2 Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská dolina, 842 48 Bratislava, Slovakia
3Space Research Centre, Polish Academy of Sciences, 51-622 Kopernika 11, Wrocław, Poland
Abstract
The contribution present results of joint analysis of RHESSI continuum and RESIK line flare spectra. We show that RHESSI non-thermal component (> 20 keV) associated with the electron beam is well correlated with
presence of non-thermal n-distribution of plasma electrons obtained from the RESIK spectra at ∼ 2 keV. In addition, such an n-distribution occurs during radio bursts observed in the 0.61 - 15.4 GHz range. Data also suggest
that the n-distribution could also explain RHESSI emission below ∼ 5 keV. Finally, on the basis of spectral line analysis we argue that the n-distribution does not occupy the same location as the thermal component detected
by RHESSI at ∼ 10 keV.
Data Analysis
RESIK
RHESSI
In the soft X-ray range, ∼ 2 keV, Si lines observed by RESIK3 are analysed assuming a so-called
n-distribution of the plasma electrons
In hard X-rays we use RHESSI2 data and assume emission is composed of continuum emission (protonelectron bremsstrahlung) plus contribution of Fe (∼ 7 keV) and Fe-Ni (∼ 8 keV) line complexes. Above
∼ 6 keV RHESSI spectra were forward-fittted with an iso-thermal component and a thick-target nonthermal emission of a power-law electron beam.
fn(E) ≈ E n/2(kT )−(n/2+1) exp(−E/kT )
τ = (n + 2)T /3 ,
which has enhanced and narrower peak than Maxwell distribution for high n, see Fig. 1, left. Diagnostics of the n-distribution is based on line ratios1 of two allowed lines SiXIII and SiXIV and a satellite
line SiXIId, see Fig. 1, centre and right.
The n-distribution should also contribute to the bremsstrahlung emission. When the data allowed it, we
explored lowest RHESSI energies, from 4 keV, and included thin-target n-distribution emission into the
fit.
Figure 1: Left: n-distributions, Centre: example of RESIK spectrum together with synthetic spectrum corresponding to n-distribution and Maxwell distribution. Left: synthetic line ratios as functions of n (—) and τ (- - -).
1 Dzifčáková, E. et al. :2008, A&A, 488, 311
2 Lin, R. P. et al.:2002, Sol. Phys., 210, 3
3 Sylwester, J. et al.: 2005, Sol. Phys., 226, 45
Results
• presence of the power-law component in the RHESSI spectra is well correlated with non-thermal
n-distribution n ≥ 5 obtained from RESIK - see Fig. 2
• RHESSI spectral fits from 4 keV require an additional component consistent with the n-distribution
obtained from RESIK - see Fig. 3
SPEX HESSI Count Flux vs Energy with Fit Function, Interval 0
102
SPEX HESSI Count Flux vs Energy with Fit Function, Interval 0
102
Detectors: 4F
7-Jan-2003 23:28:32.000 to 23:28:52.000 (Data with Bk)
7-Jan-2003 23:28:32.000 to 23:28:52.000 (Bk)
100
counts s-1 cm-2 keV-1
counts s-1 cm-2 keV-1
100
10-2
10-4
Detectors: 4F
22-Feb-2003 09:28:12.000 to 09:28:20.000 (Data-Bk)
22-Feb-2003 09:28:12.000 to 09:28:20.000 (Bk)
Fit Interval 0 Chi-square = 1.31
vth+photon_thick+drm_mod+thin_ndistr
vth 0.00347,2.44,1.00 full chian 1.26e-04
photon_thick 2.39,6.50,200.,8.00,15.5,1.00e+03
drm_mod 0.837,0.00851,1.00
thin_ndistr 0.0451,1.72,6.50,1.00e+03
10
10-2
10-4
Fit Interval 0 Chi-square = 1.12
vth+photon_thick+pileup_mod+drm_mod+thin_ndistr
vth 0.00851,1.86,1.00 full chian 1.26e-04
photon_thick 0.465,2.87,200.,18.0,9.78,1.00e+03
pileup_mod 1.19,0.900,1.00,10.0,3.00,0.500
drm_mod 0.608,0.0777,1.00
thin_ndistr 0.0507,1.63,11.0,1.00e+03
100
10
100
Energy (keV)
Figure 2: Examples of time evolutions of n (- - -) obtained from RESIK and δ (—) of RHESSI power-law component for
two flares (7-Jan-2003, 22-Feb-2003).
• n-distribution of n ≥ 5 occurs during radio bursts in the 0.61 – 15.4 GHz range - see Fig. 4
Energy (keV)
Figure 3: RHESSI spectral fits of two flares (7-Jan-2003, 22-Feb-2003) composed of the n-distribution (—, —), iso-termal,
and power-law component.
• due to sensitivity of the Si XIId line to the distribution shape around ∼ 2 keV, see Fig. 5 left, emission
related to the n-distribution plasma comes from a different substructure than the iso-thermal emission,
although RHESSI corresponding sources (3 – 6 keV and 6 – 12 keV) are almost co-spatial (Fig. 5,
right)
Reconstructed RHESSI Image
Heliocentric Y (arcsec)
410
Figure 4: Example of correlation of radio emission
and non-thermal n-distribution for the 7-Jan-2003
flare. Heavy thick line denotes times of n ≥ 5, gray
line denotes times of n < 5 as obtained from RESIK.
22-Feb-2003 09:28:12.000 to 09:28:20.000
Detectors: 3F 4F 5F 6F 7F 8F
Energy Range: 12.0 - 25.0 keV
Clean Total counts: 2.53E+04
400
390
380
370
50
60
70
80
90
Heliocentric X (arcsec)
WHITE: dash line - 25-50keV, 70%
WHITE: dash dot line - 6-12keV, 70%
WHITE: solid line - 3-6keV, 70%
420
100
Figure 5: Left: schematic figure indicating which parts of a distribution influence intensities of Si lines used in the RESIK
diagnostics, Right: RHESSI image of the 22-Feb-2003 flare.
Conclusions
Acknowledgements: Authors acknowledge grants No. 1/0240/11 (Scientific Grant Agency VEGA, Slovakia), 205/09/1705
and P209/10/1680 (GAČR), IAA300030701 (GA AS CR), N203 381736 (Polish Ministry of Science), 218816 (FP7/20072013), and research project AV0Z10030501.
Two independent methods and data sets indicate a non-thermal electron distribution in the 2 – 5 keV
range. RESIK data suggest that n-distribution plasma does not occupy the same structure as the thermal
plasma. For the first time the RHESSI excess emission below ∼ 5 keV is fitted and explained as due to
the n-distribution. RHESSI and RESIK n-distribution parameters agree within uncertainties:
22-Feb-2003: nRHESSI = 2 − 9 (≥ 4.5)RESIK kτRHESSI = 1.0 − 1.5 keV (1.16 − 1.57)RESIK
07-Jan-2003: nRHESSI ≥ 5 (≥ 3.3)RESIK
kτRHESSI = 1.5 − 2.6 keV (0.94 − 1.46)RESIK
For more details see Kulinová, A. et al.: 2011, A&A, submitted.