n-distribution
Transkrypt
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.