Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/external/xmm_sw_cal/icwg/presentations/INTEGRAL_SPI.pdf Дата изменения: Mon Jun 19 12:53:14 2006 Дата индексирования: Sat Dec 22 14:51:41 2007 Кодировка: Поисковые слова: stonehenge

SPI
Imaging : 16° fully coded FOV Angular resolution : 2.6° Energy range : 20 keV- 8 MeV Energy resolution : 0.2 % Time resolution : 100 microsec Shield : active BGO shield Camera :19 HPGe detectors. Active cooling : 85 K


CAMERA CONCEPT
19 Hex detectors 85 K stage Annealing : 105 C 210 K stage Preamp at 210 K Beryllium cryostat


SPI CALIBRATIONS 4 STEPS : - CAMERA CALIBRATION : After camera integration (Sept 2000) - SPI CALIBRATION AT CNES After SPI integration (Dec 2000) - SPI AT THERMAL TEST SPI in representative thermal conditions (March - April 2001) - SPI CALIBRATION AT BRUYERES LE CHATEL Latest calibration before SPI delivery at ESA (April - May 2001)


SPI FM CALIBRATIONS


CALIBRATION SYSTEM : GUN (Sources collimator)

The following sources had been used : 137Cs / 60Co / 241Am / 24Na / 85Sr / 54Mn / 88Y /

109

Cd /

228Th

/ 57Co


Single event spectra simulation and measurement for the central detector. Radioactive source : 85Sr

---- Measurement ---- Simulation


SPI CALIBRATION AT BRUYERES LE CHATEL (May 2001)


CALIBRATION SCHEME
SPI without coded mask : Test efficiency and homogeneity

- Short distance sources (low intensity, 8 m).
11 different radioactive sources . Energy range : [60,1836] keV. - 4 MeV-van de Graaf accelerator, calibration up to 8062 keV. SPI with coded mask : Test of imaging - Long distance sources (high intensity,125 m), Energy range : [60,2753] keV.


IMAGING PERFORMANCES

2.7 MeV


Response matrix generation by Monte-Carlo simulation


Instrument Response: Overview
· A detailed mass model was created "by hand" based on technical drawings. · Several "compression" schemes were devised to make the MC problem manageable in terms of CPU and storage. · Simulations of the BLC calibration were performed at GSFC using the mass model and "MGEANT" MC SW. · Comparison of these simulations with data led to improvements in the MC software and the mass model.


Instrument Model
These cutaway views give an idea of the level of detail in the SPI instrument model, which has been integrated with the Southampton "TIMM".

SPI cut-away views

TIMM-3


Instrument Response Corrections
Mask honey-comb support transmission correction curve. Points are the measurements for 4 offset angles, and the curves are from MC simulations.

Photo-peak effective area correction factors for single, double & triple events. Extrapolation to Lowest and highest energies.


IRF Compression
· The computational problem scales as ~Nsky x Ndet x Nch, per mono-energetic input energy with statistics at each vertex, which becomes unmanageable · Savings was achieved first, by tracking detailed MC events for vertices within single a "piewedge" subset of the detector array · This is then convolved with a full (i.e. all directions) database of absorption path-lengths derived from the ray-tracing events


IRF Compression
· This leads to 2 large, databases of
­ spectra per detector-array vertex per direction (DMATRIX) ­ absorption path lengths per direction (over sampling instrument resolution by ~5X (LMATRIX)

· From these, the basic response data set, or IRF is created
­ 5 dimensional object, NE x N x N x Ndet x Nspc-cmp ­ this comprises the basic end-user response database which is used directly in image reconstruction ­ and from which XSPEC "ARFs" are extracted


Response Decomposition
The response is approximated as a convolution of ray-tracing and detailed photon-propagation terms:

R(d , , , E , ch) =



Li (d , , , E ) Di(d , , , E , ch)

Further computational and storage economy are achieved by recognizing that the response continuum can be reconstructed as a linear combination of components.


IRF Calibration
On-axis, total efficiency. Blue is uncorrected IRFs. Data points are 133Ba and 241Am measurements from CEA. Red curve is the recalibrated IRF.


SPI Crab Nebula observations


THE CRAB NEBULA 20-50 keV 567 ks


Crab Nebula Stability in the FOV Rev 300 10° circle around the axis


Crab Nebula - Calibration stability ­ revolutions 300 and 45


Crab Nebula observations


Whole camera peak positions in keV and energy resolution
438.634 keV 438.634 keV

0.015 keV

438.645 keV

1778.969 keV
0.015 keV

1778.969 keV

1778.961 keV

882.5 keV

882.5 keV

0.015 keV

882.50 keV