RHESSI Spectroscopy of Thermal
Solar Flare X-ray Emission
Cristina Chifor (a)
Ken Phillips (b) , Brian Dennis
(c)
a) DAMTP, University of Cambridge, UK
b) Mullard Space Science Lab, UK
c) NASA/GSFC, Maryland, USA
‘X-ray Spectroscopy and Plasma Diagnostics From the RHESSI,RESIK and
SPIRIT Instruments’ 6-8 December 2005
Wroclaw,
Page 1Poland
Presentation Outline
 Reuven Ramaty High Energy Solar Spectroscopic
Imager: Data Access and Analysis
 Fe Line Complexes : Observations with RHESSI
 RHESSI / RESIK Cross - Calibration
 How to get more help with RHESSI data & analysis
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RHESSI
Reuven Ramaty High Energy Solar Spectroscopic Imager
NASA Small Explorer
Imaging and spectroscopic
observations of solar flares
since February 5th, 2002
Principal Investigator:
Robert Lin, UCB
Lead Co-investigator:
Brian Dennis, NASA/GSFC
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RHESSI
Reuven Ramaty High Energy Solar Spectroscopic Imager
9 cylindrical cooled Ge
detectors (< 75 K)
Energy range:
5 keV to 17 MeV
(~ 8 mÅ to 2.5 Å)
FWHM ~1 keV (12.4 Å) in
the “soft” X-ray range
(“soft” ~ up to 20 keV)
Movable shutters, high-rate
electronics with “pile-up”
suppression
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How to Access RHESSI Data ?
Object Oriented Software & GUI
Distributed through the Solar Software package
SSWIDL (hessi)
http://hesperia.gsfc.nasa.gov/ssw/hessi/doc/
hessi_data_access.htm
RHESSI DATA:
1. Flare catalogue
2. “Quicklook” plots
3. Level 0 Telemetry Data
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RHESSI Data I: Flare Catalogue
Up to date text and binary FITS file
Currently, containing more than 18,000 flares
INCLUDING…:
FLARE CATALOGUE NO.
START, PEAK & END TIMES
DURATION
PEAK COUNT FLUX (C/S)
ENERGY RANGE
X, Y COORDINATES (ARCSEC)
FLAGS (i.e attenuator state, night-time, SAA )
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RHESSI Data II: « Quicklook »
Daily FITS files in the metadata/catalogue directory of the
RHESSI data archive
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RHESSI Data III: Level 0 Telemetry Data
Packets in FITS files (up to ~ 110 Mb)
One FITS file/single orbit between local midnights
Multiple FITS files for large flares
http://hesperia.gsfc.nasa.gov/hessidata/
GSFC (Maryland)
ftp://hercules.ethz.ch/pub/hessi/data
ETH (Switzerland)
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Spectral Analysis Overview I
STEP 1. Generate count
rate spectra.
hessi -> RHESSI GUI
OUTPUT:
Count spectrum file
+
Response Matrix
(srm) file
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Spectral Analysis Overview II
STEP 2. OSPEX. Obtain
photon spectra + models.
obj = ospex()
INPUT:
Count spectrum file
+
Response Matrix
(srm) file
Until recently, used MEWE
spectral model.
Now changed to CHIANTI.
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"RHESSI Observations of the Iron - Line
Feature at 6.7 keV”,
Phillips, K. J. H., Chifor, C. , Dennis, B.
- submitted to the Astrophys. J
Motivation
 RHESSI observes both continuum and Fe line complexes
(at 6.7 keV and 8 keV)
 How does the empirical Fe/H abundance ratio in flares
vary with Te ?
 How do empirical correlation curves compare with
theoretical curves calculated with coronal Fe abundances ?
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Flare Sampling Criteria
 Isothermal approximation OK in the late decay stages
 So, choose long duration, slowly decaying flares
 Used GOES to select flares according to this criteria
Example: GOES fluxes, high-energy band (~ 25 keV) lightcurves for July 2002
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Sampled Flares
 30 flares between 2002 - 2005
 GOES X-ray classification: C3 – X8
 More than 2000 spectra of 20 – 60 s in the
decaying stages of these flares
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Spectral Modeling
I. RHESSI GUI: spectral file + SRM file
Energy bins: 1/3 keV in the 3 - 20 keV range
1 keV in the 20 – 100 keV range
Time bins: 20 – 60 s
Optional pulse pile-up corrections ( rate > 1000 counts/s)
II. Input the 2 files in the Object Spectral Executive (OSPEX)
Background subtraction
One isothermal component to fit continuum + 2 Gaussian
lines (1 keV FWHM) centered at ~ 6.7 and 8 keV to model the
Fe and Fe/Ni complexes
Reduced chi-squared for best fit
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Some Instrumental Issues
 High count rates in RHESSI detectors decrease
energy resolution in the soft X-ray range and
increase calculated T.
 “pulse pile-up” problems at high count rates
 Therefore, for now, avoid A0 attenuator states
(i.e. when no shutters are in front of detectors)
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May 31st 2002 M2 Flare
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Chianti 5.0
Coronal
abundances
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Fe Line Complexes:
Summary & Conclusions
 Survey of > 30 RHESSI flares (GOES class C3 - X5)
 Fe line features observed by RHESSI at 6.7 keV indicate a
coronal abundance of Fe for the emitting flare plasma.
 Some differences between the observed and theoretical
EW’s of the lines may be due to:
 Non-isothermal nature of the flare plasma (in
particular at and shortly after the flare peak)
 Instrumental effects such as the resolving of the
line features at high count rates
 Possible errors in atomic rates used in theoretical
He-like Fe ion fractions. Page 19
RHESSI vs. RESIK
A number of coincident flares: cross-calibration possible.
RHESSI low energy end ~5 keV
RESIK in 1st -order mode observes from 2.0 to 3.7 keV
RESIK in 3rd–order mode sees Fe line feature at 6.7 keV
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RHESSI vs. RESIKord.1 vs. GOES
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Getting Help I: RHESSI Home Page
http://hesperia.gsfc.nasa.gov/
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Getting Help II: Data & Software Center
http://hesperia.gsfc.nasa.gov/rhessidatacenter/
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RHESSI Nuggets
http://sprg.ssl.berkeley.edu/~tohban/nuggets/
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Thank you !
Thank You !
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Counts/s/cm2/keV
Fe Line Complexes: RHESSI Observations
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