Upload
rodney-cobb
View
213
Download
0
Tags:
Embed Size (px)
Citation preview
Spectral Breaks in Flare HXR Spectra
A Test of Thick-Target Nonuniform Ionization as an Explanation
Yang Su NASA,CUA,[email protected]
Gordon D. Holman NASABrian R. Dennis NASA
Napa, CA Dec.10.08
1/2 Nonuniform Ionization1/3-1/2: Introduction 2/3-1/2: Models3/3-1/2: RHESSI Observation
2/2 Time evolution and Imaging spectroscopyFlux of one source from Clean, Pixontime evolution of spectral breaksImage Spectroscopy, spectra from footpoin
ts (spectral breaks)
Solar flare HXR spectrasingle / double power-lawtime evolution (Dulk et al. 1992; Lin &
Schwartz 1987)break energy: typically between ~50 and 100
keV
Spectral breaks is importantacceleration mechanismselectron propagation and energy lossesrelationships between flare X-ray sources,
radio sources, and particles
1/3-1/2 Introduction
For the count and photon spectraInstrumental effects, such as pulse pile-
up (Smith et al. 2002)Additional components, such as:
Albedo (Kontar et al. 2006; Kontar & Brown 2006; Zhang & Huang 2004)
emission from thermal plasma
1/3-1/2 Introduction
For the accelerated electronsNon-power-law electron distribution from the
acceleration process, e.g. a double power-law electron distribution a low-energy cutoff (Gan et al. 2002; Sui et al. 2007) a high-energy cutoff (Holman 2003)
An anisotropic electron pitch-angle distribution (Petrosian 1973; Massone et al. 2004)
Beam-plasma instability (Holman et al. 1982; Melrose 1990)
Return current energy losses (Knight & Sturrock 1977; Zharkova & Gordovskyy 2006)
Nonuniform target ionization (Brown 1973; Brown et al. 1998; Kontar et al. 2002)
1/3-1/2 Introduction
AimsSpectrum from nonuniform ionization
thick-target with full cross sectionCan nonuniform ionization model exp
lain the spectral breaks in observations?
And how many?
1/3-1/2 Introduction
Nonuniform target ionizationElectron energy losses lower in un-ionized or
partially ionized plasma than in fully ionized plasma
Brown et al. 1998, x(N) is the ionization level
2/3-1/2 Model
effective column density M
step-functionBrown 1973, Kontar
et al. (2002)the atmospheric
ionization
the Kramers approximation of the cross section, q=1
linear-functionthe atmospheric
ionization
When N0 = N1=N*, step function
full relativistic cross section of Bethe and Heitler
2/3-1/2 Model
step linear
1
0
0
1
0
E*=E1=30 keV
Ee=60 keV stops here (M0)
N
N1
N0
2/3-1/2 Model
δ=4.5 (best fit γ=3) (Brown 1973)
2/3-1/2 Model
Relation between N and E
Photon flux from linear-function model
Fc=1035 electrons s-1; Ec= 1 keV
(=0 for N1=N0)
2/3-1/2 Model
Photon spectra and photon spectral index γ from the four models with δ=4 Arrows: upward knee, downward knee and γ(ε) for fully ionized model (not constant)
Spectra from linear-function model with fixed E1 and increasing E0
2/3-1/2 Model
RHESSI flare sample2002 February 12 - 2004 December 31. Non-solar
and particle events were excluded.12-25 keV count rate > 300 counts s-1 detector-1.
the 50-100 keV count rate to be at least 3σ above the background count rate. (F50)
Radial distance > 927” from disk center (>~ 75 degrees longitude at the solar equator) This minimizes the impact of albedo on the X-ray
spectrum (Kontar et al. 2006)
Detector corrected count rate live times> 90%. This gave a final sample size of 20 flares. This minimizes the impact of pulse pile-up (Smith et al.
2002; Ka·sparov¶a et al. 2007).
3/3-1/2 RHESSI Observation
1/3 keV bins from 3 to 15 keV and 1 keV bins above 15 keV
All RHESSI front detectors no 2 and 7 -- poor energy resolution no 5 for the 30 Nov 2003 flare -- unusually low livetime no 8 for some flares -- interference from RHESSI's
communication antenna One spin period, mostly at the HXR peak time Full RHESSI response matrix, instrumental
systematic uncertainty: zero (Sui et al. 2007) Isothermal + three spectral lines+ nonthermal mo
dels Two steps for fit, first fit above 6 keV, then fix thermal
comp. then fit above 15 keV the ion line complex at ~6.7 keV the ion/nickel line complex at ~8 keV (Phillips 2004) and a nonsolar line at ~10.5 keV
CLEAN Images : 40-60 keV for same time interval
3/3-1/2 RHESSI Observation
Examples for poor fit (left) and good fit (right)
3/3-1/2 RHESSI Observation
fit results from:Bpow fitF_ion fit (Kramers)N_ion fit (full cs)
∆γ VS δ∆γ from bpow fitδ from step-function fit
3/3-1/2 RHESSI Observation
full cs and Kramers (up to 36% on flux and 6.8% on γ)
step and linear upper limit on ∆γ of spectra from non
uniform ionization model In 20 F50 flares (around peak)
5 with single , 15 with broken 10 out of 15 F50 flares can not be explained by
nonuniform ionization alone All the 5 that can be explained by non-ion have
DF sources
-1/2 Summary
Aims: spectral breaks VS time How HXR sources change when the
spectra change from single to b-pow
spectrum from each footpoint relation between spectral breaks for f
ootpoints and total spectrum
2/2 Time evolution and Imaging spectroscopy
Flux from single source of one image:flare id: 4010604, 22:32energy range: 40-60 keV
2/2 Time evolution and Imaging spectroscopy
pixon D2-D8, -973.855, 75.125, 9 32.147 pixon D2-D8, including background model , 32.106
Clean D2-D8, different iterations, 300, stop if, 46.290
Normal, no stop MM=Media Mode50: 51.356 50: 30.223100: 43.952 100: 33.154300: 37.070 300: 34.189 500: 35.290 500: 34.456 700: 34.434 700: 34.5291000: 33.751 1000: 34.667
Clean D2-D8, 4.06s100: 43.996 100: 33.311300: 37.001 300: 34.1961000: 33.477 1000: 34.514
2/2 Time evolution and Imaging spectroscopy
150-250 keVPixon: center -972.855, 73.125, circle:9, 2.4521 Flux Area Centroid (X,Y) Peak (X,Y) St Dev (X,Y) Peak2.4521 290.00 -973.92 72.75 -973.28 73.15 3.94 3.95
0.026954
Clean D2-D9, different iterations300, stop if, 6.5105 MM: 4.0746Normal, MM50: 5.3177 50: 4.2477100: 3.9565 100: 4.4367 300: 1.8182 300: 4.5518 500: 1.1578 500: 4.5647 700: 0.9261 700: 4.5654
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
2/2 Time evolution and Imaging spectroscopy
?/? The highest HXR source???
To be continued?/? Direct observation of reconnection???