RHESSI Observations and DataAnalysis

Nicole Vilmer

LESIA-Observatoire de Paris

Tostip- October 2003

• The (R)HESSI (Ramaty High Energy Solar Spectroscopic Imager) Experiment

• Scientific goals and objectives• What do we know about energetic particles at the Sun from HXR/GR observations?

• General Description of the Instrument• How to make images at X-ray/-ray wavelengths with Rotation Modulation Collimators?• How to make X-ray/-ray spectra at high energies?

• How to access to data and analyse data?Time profiles

Images (co-alignment) Spectra

RHESSI scientific goals • The Sun as an efficient particle

accelerator:(large fraction of the flare energy release)

• High Energy Solar Physics

• Flare energy release• Particle acceleration/transport and

interaction in the solar atmosphere• Large Flares BUT ALSO• Microflares: coronal heating??

Solar Physics special issue 210

Principal Investigator:   Robert Lin UCB

Project Manager:   Peter Harvey UCB

 Lead System Engineer:   David CurtisUCB

Lead Co-Investigator:   Brian Dennis GSFC 

Co-Investigators:   Arnold Benz ETHZPatricia Bornmann NOAAJohn Brown U. of GlasgowRichard Canfield Montana State U.Carol CrannellGSFCGordon EmslieU. Alabama Huntsville Shinzo EnomeGordon HolmanGSFC, Code 682Hugh Hudson UCB Gordon HurfordGSFC,Code 682Takeo KosugiNAOJNorman Madden LBNLReuven RamatyGSFC, Code 661Frank van BeekDelft U.Nicole VilmerParis ObservatoryTycho von RosenvingeGSFC, Code 66Alex ZehnderPSI

         

31/01/2002

Launched on 05/02/2002

Solar data from 14/02/2002

Catalog of RHESSI X-ray flares from 14/02/2002 to 05/20038000 flares > 12 keV Several GOES X-class flares (at least one -ray line flare)

Several X-flares May-June 2003

http://hesperia.gsfc.nasa.gov/ssw/hessi/dbase/hessi_flare_list.txt

Flare Accelerated Particles

• Particle acceleration (Where, How Fast? How Many? Which Ones?)

• Particle transport and interaction in the atmosphere (How do they evolve in the ambient medium?)

• Injection in the interplanetary medium (Where? When? Relation with flare particles?)

Solar X-ray/-ray spectrum

RHESSI Energy range

Pion decay radiation(ions > 100 MeV/nuc)sometimes with neutrons

Ultrarelativistic ElectronBremsstrahlung

Thermal components

Electronbremsstrahlung

-ray lines (ions > 3 MeV/nuc)

• Direct diagnostics of energetic particles interacting in the solar atmosphere:HXR and GR continuum:

~ electrons 10 keV-~100 MeV (acceleration timescales,

number and energy spectra)

No imaging above 70 keV

Limited spectral resolution

No imaging spectroscopy

(R)HESSI

Unique observation at high spectral resolution before RHESSI

From Lin et al. 1981

Energetic Ions -ray line spectroscopy ions in the 1MeV/nuc-100 MeV/nuc range

narrow deexcitation -ray line fluences ion energy spectrum

and target abundances(i.e. solar atmosphere) • Broad -ray lines

abundances of accelerated ions

2.2 MeV deuterium line:capture line after thermalizationfrom neutrons from nuclear reactions

(Share & Murphy,2000)

-ray line spectroscopy before RHESSI

• 19 GRS/SMM /1 CGRO/OSSE flares (Share & Murphy, 1995, 1998)

• Ion energy spectrum from Ne (1.63)/ O (6.13):power laws down to 1 MeV/nuc and ion energy content but also dependant on abundances

/p(5 flares) fromFe(0.339)/Fe(0.847).Fe (0.339) is a pure line

/p = 0.5

• 3He/4He (7 flares) 0.1 to 1(Ramaty & al , Mandzhavidze & al )

Share & Murphy (1995)

Ramaty &

Mandzhavidze, 1995

O (6.13)Ne (1.63)

Electron/Ion Energy Contents in G GRL flares (before RHESSI)

• We>20 keV and Wi>1MeV/nuc

19 SMM Flares,1 OSSE, 1 GRANAT

(Ramaty & Mandzhavidze, 1999)(Murphy et al, 1997, Ramaty et al, 1997)

But low energy cutoffs?Better spectral resolution at X-rays electrons

Low energy ions?What happens in electron-dominated events?

Adapted from Ramaty & Mandzhavidze (1999)

•Wi>1MeV/nuc for 19 SMM flaresWe>20 keV for 19 SMM flaresWi>1MeV/nuc for OSSE 4 June 1991‣Wi>1MeV/nuc for PHEBUS 1 June 1991

X/-ray observations and acceleration processes

• Additional constraints

Variability of spectra

e/p in flares &

from flare to flare

( electron-dominated

events)

Enrichment of /p,

3He,

heavy ions (Ne,Mg, Fe)

as in impulsive SEP events

Variation with time of the enhancements

Electrons Ions

Number 1041 (>20 keV) 310 35 (>30MeV)

1036 (> 100 keV) 10 32(> 300

MeV)

Acc. times ~ 100 ms @100 keV

< 1s @10 MeV

Duration (s) 10 ~10 mn 60 hour

Total energy (ergs)

10 34 (> 20 keV) 10 32- 10 33 (> 1 MeV)

10 29 (> 100 keV) 10 30 (> 30 MeV)

Power (ergs/s)

10 32 (> 20 keV) 2 10 28 (> 30 MeV)

Adapted from Chupp, 1995

RHESSI Characteristics• Imaging

• Angular resolution

• Field of View

• Pointing information:• Solar Aspect System (SAS)• Roll Angle Systems (RASs)• Spectroscopy• Energy range• Energy resolution

• Fourier-transform imaging with 9 bi-grid rotating modulation collimators

• 2.3 to 36 depending on energy• HXR 2.3 ; GRL /GR 36 • Full Sun• Tens of ms for basic image• 2s for detailed image

SAS: Sun center <1’’

RASs: roll to 1’

• 3 keV to 10 MeV• < 1 keV 5 keV@ 20 MeV

RHESSI Spectroscopy• 9 bi-segmented n Germanium

detectors front (1.5cm): 3 keV-250 keV rear (7.5cm): 250 keV- 17MeV• 7.1 cm 8.5 cm length• Cooled to < 75K 2 sets of aluminium disk attenuators (shutters) to absorb low energy photons in case of large flares (see obs summary plots)

GRL spectrum simulated

for HESSI for a large flare(Smith et al, 2000)

Instrument Data Processing Unit:

Photons interacting in the GeD generate charge pulses collected and amplified by charge sensitive amplifiersThis provides Counts

Front segment: 8192 energy channels from 3 keV to 2.7 MeV (0.33 keV/channel)Rear segment: 20 keV to 17 MeV For each photon: energy information time of arrival to 1 s with detector & live timeAll these information in the fits files

RHESSI: Spectroscopy

RHESSI Imaging

• Grids • 8 pairs tungsten• 1 molybdenum• Pitch: 34- 2.7mm (steps

of 3• L=1.55m• Fast rotation: 12-20 rpm• Dynamic range:100/1• 1100 uv components in 2s• No modulation for>3’ but still full spectroscopic info

Grid 1 (2.2’’): slit and slat widths: 20 and 14 Max energy for modulation: 100 keV (1.2mm thick)

One of the thickest grid (18.6mm)used to modulate

photons up to 17 MeV (35’’)

RHESSIImaging

Angular resolution : p/2L

Arrival time and energy Of each photon

Aspect systems:

Need to know the orientation of the collimators with respect to the direction of the Sun

Provided by SAS (Solar Aspect System): measurements relative to the solar limbs to ‘’ accuracy on 10ms

and 2 Roll Angle Systems: a CCD RAS and a PM based version (PMTRAS Photo-Multiplier-

Tube Roll Aspect System) currently used in the software providing roll angle to ‘ accuracy several times per

rotation with respect to fixed stars. It views the star field perpendicular to the Earth-Sun line and records times at which bright stars pass through the field of view.

23/07/2002 X4.8 GOES: RHESSI -ray line flare

Lin et al, 2003

Images:64’’ wideAt the time of flare maximum

Krucker et al,2003

30 –80 keV every 27s

X4.8 flare : 23/07/2002-X-ray spectroscopy with RHESSI

Holmann et al, 2003

Piana et al, 2003

Spectre photonsT=37 MK EM= 4.1 10 49 cm-3

Thin target radiation double power lawEc= 34 keV l=1.5 Eb=129 keV u=2.5

Inversion of the photon spectrum

Electron spectrum

Extrapolation above 160keV

X4.8 flare : 23/07/2002 Imaging spectroscopy with RHESSI

Emslie et al, 2003

N

M x0.1

Sx0.01

Photon spectrum

Lin et al, 2003

Share et al, 2003

Spectral analysis every 20s:6 narrow -ray linesElectron bremsstrahlung:2 power laws 2.77 et 2.23 > 617 keVBroad line component511keV and 2.23 MeV lines

Smith et al, 2003

Redshift (0.1-0.8 %)larger than expectedfor a limb flareif Downward isotropic distributionif Radial B field!

SMM 5 flaresSame longitude

Broadening 0.1-2.1% FWHM

No redshift (light curve) Redshift (Heavy curve)

First gamma-ray images of a flare!

Gamma-ray line image displaced from20 ’’ from electron emission site!!! Interpretation? Hurford et al, 2003

+ TRACE post flare loop

Coronal HXR sourcesGOES M2.5 AR 9893AR 9893 N21 W81 large part behind the limbH 1310-1320-1332 N23 W88 SF AR 9893 < 1323- 1338 N19 W67 SF AR9901

Coronal HXR source from 13:07 UT

H 8 days earlier

Vilmer, Koutroumpa, Kane, Hurford, EGS

Comparison of RHESSI images with TRACE images at 195 Å =flare plasma at 15 MK(coalignment between EIT and Trace during the flare)

TRACE and RHESSI 12-25 keV images before 13:07 UT (no coronal HXR sources)

TRACE and RHESSI 12-25 keV

images after 13:07 UT(coronal HXR

sources with most of the time no

footpoints Most energetic part of the

event)

TRACE and RHESSI 25-50 keV images after 13:07 UT(coronal HXR sources with most of the time no footpoints Most energetic part of the event)

•Coronal HXR sources (> 10’’ ) above the limb, displaced from the hot magnetic structures seen with TRACE?•25-50 keV predominant coronal sources above 12-25 keV sources (faint footpoints close to max)•(see previous YOHKOH/HXT obs but more dynamical and more complicated fields?)

RHESSI & UV & Optical Observations (B. Schmieder, A. Berlicki, G. Aulanier, N. Vilmer, DPSM)

22 oct 2002

B long (NaD1, THEMIS)B long (NaD1, THEMIS)

HXR 6-12 keV HXR 6-12 keV (RHESSI)(RHESSI)

Decay phase of GOESM flare

RHESSI & Optical Observations (B. Schmieder, A. Berlicki, G. Aulanier, N. Vilmer, DPSM)

22 oct 2002

B long (NaD1, THEMIS)B long (NaD1, THEMIS)

I (NaD1)I (NaD1)

Éruption HÉruption H (VTT)(VTT)

HXR 6-12 keV HXR 6-12 keV (RHESSI)(RHESSI)

RHESSI & SOHO JOP 136 CDS FLARE_AR

6-12keV

How to access and analyse data?A few addresses

Data at

http://hesperia.gsfc.nasa.gov/hessidata/ ftp://hercules.ethz.ch/pub/hessi/data

Level 0 packets in fits files (up to 110 Mbytes)

one fits file/single orbit between local midnights

multiple fits files for large flares

Software : sswidl (hessi)http://hesperia.gsfc.nasa http://hessi.ssl.berkeley.edu/software/ Objcct oriented software but also Graphical User Interface (GUI)

A few « quicklooks »: http://sprg.ssl.berkeley.edu/~ayshih/browser/quicklook.shtml

http://rhessidatacenter.ssl.berkeley.edu/

http://sprg.ssl.berkeley.edu/~ayshih/browser/grw.shtml

How to make light curves: the observing summary plots

Look at decimation and attenuators states

Need to get observing summary files hsi_obssumm_*.fits files (see hands-on

How to make light curves?

How to make images• From the modulation time profiles:

inverse problem of deducing the source geometry given a set of modulation profiles from different subcollimators

• Several image reconstruction algorithms:

• « back projection »: initial estimate of the image, convolution of the image with the instrumental response

sidelobes• To improve the quality: CLEAN,

MEM,pixon,…

• Not to expect the kind of images with the morphological richness of TRACE, YOHKOH/SXT, SOHO/EIT!!!

How to make images• Back projection: equivalent to 2D inverse Fourier transform analog to radioastronomers’ dirty maps.

linear process (not the case of CLEAN,MEM,…)

Deduction of the source geometry given the set of observed modulation profiles from different subcollimators oriented according to the roll angles.

importance of the aspect solution!!! PMTRAS by default sometimes necessary to change to RAS (Roll Data Base still in progress)

Some useful addresses:LISTING OF ROLL DATABASE GAPS > 66 SECONDShttp://sprg.ssl.berkeley.edu/~ghurford/ROLL_DBASE/ROLL_DBASE_GAPS.txt

Index of /hessidata/metadata/data_gap_files/daily_summaryhttp://hesperia.gsfc.nasa.gov/hessidata/metadata/data_gap_files/daily_summary/

Some examplesGrid 3

Grid 4

Grid 5

Grid 6

Grid 7

Grid 8

Grid 9

Clean: iterative algorithm developed for radio astronomy

based on the assumption that the image is a superposition of point sources

How to compare with other images

Use the synoptic archive software to get fits files from other instruments

Use the mapping software of Dominic Zarro to overlay (see hands-on)

!!! Some special treatments may be needed for TRACE see http://hesperia.gsgc.nasa.goc/~ptg/trace_align

How to make spectra?Photons interacting in the GeD generate charge pulses collected and amplified by charge sensitive amplifiersThis provides Counts which are recorded in the fits files

• 9 bi-segmented n Germanium detectors front: 3 keV-250 keV (NOT DETECTOR 2 (7)) rear: 250 keV- 17MeV

!!!Attenuators reduce the count rates in case of large flares

!!!If the memory starts to fill up a decimation algorithm throws out one out of every N events in the front segment below a

given energyAlso indicated in the observing summary plots;Now corrected for spectroscopy.

How to make spectra

!!! Pile up correction for large flares (also 1st order correction for spectroscopy)

Pulse pile up: 2 or more « low energy photons arrive ‘simultaneously’ and cannot be distinguished from a single high energy photon.

Artefact for spectroscopy but also for imaging: low energy count-rate may appear at higher energies;

« ghost » low-energy sources appearing at high energies

How to make spectra

• The background issue:

RHESSI is not a low background instrument. But for most events, flares are brighter than the background!!

Background issues important for -ray flares, at low energies

for flares with attenuators…

Sources of variation of theRHESSI background:•Passes through SAA•Changes of geomagnetic latitudes•Electron precipitation from belts at 40-50° latitudes (appear morestrongly in rear segments)

Spectral Data Analysis

• Inverse problem:how to go from a spectrum of counts per spectrometer channel (what is recorded) to spectrum of photons per

energy interval incident on the spacecraft • Part of the RHESSI software (SPEX spectral inversion code)

• Several steps:

• Background subtraction (count rates before and after flares, for some flares most sophisticated techniques)

• Generation of the Response Matrix: (hsi_srm_*.fits)

How to go from photons to counts?

absorption in blankets,grids,…

Compton scattering in and out the detectors,…

noise in the electronic,…

NOT A DIAGONAL MATRIX!! Except in the HXR range below 100 keV but NOT BELOW 15 keV IF SHUTTERS!!!

Spectral Data Analysis

• Inverse problem:how to go from a spectrum of counts per spectrometer channel (what is recorded) to spectrum of photons per energy interval incident on the spacecraft

• Done automatically by SPEX using forward-folding once the calibartion matrix is generated

• Input: model photon spectrum (power-laws or Maxwellian in energy + lines)

• Convolution with the reponse matrix Count spectrum • Comparison with the observed one and fit by minimizing 2

• !!!Input parameters. • !!! The reality of the fit must be checked (are the parameters found

reasonable?? Are they consistent with other observations i.e. thermal emission observed by other instruments??

•