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High Energy, High Resolution X-Ray Spectroscopy
Eric Silver
Harvard-Smithsonian Center for Astrophysics
Photon Energies > 10 keV
Measurements Important to Astrophysics, Atomic and/or Nuclear physics
Two Science Topics
Nuclear Line Astrophysics
QED Related Heavy Ion Spectroscopy
USE MICROCALORIMETERS
E E/ 1 0 0 0
Nuclear Line Astrophysics
Direct probe of one of the most violent events in the universe
a Supernova explosion that expels the heavy elements into the ISM from the nuclear furnace in which they were created
44Ti is a key diagnostic
Produced deep in the stellar core
60 year half-life
longer than the few years required for the overlying strata to become optically thin at high energies
sufficiently short that the 44Ti remains localized around the SN site while it emits intensely
Model calculations of nucleosynthesis yields for Type Ia and Type II SN show that conditions for 44Ti production are significant only within the central cores of massive stars or in white dwarfs following a surface detonation.
Mass of 44Ti is an important diagnostic of the most extreme densities and temperatures.
Vink et al. 2001
Detection of the 67.9 and 78.4 keV Lines in Cas A by Phoswich Detection
System aboard BeppoSAX
Flux of (2.1 ±0.7) x 10-5 ph cm-2 s-1
Initial 44Ti mass of (0.8 – 2.5) x 10-4 MΘ
44Ti Decay Scheme1157 keV line detected by (CGRO)/COMPTEL (Iyuden et al.1994)
Flux of (3.3 ±0.6) x 10-5 ph cm-2 s-1
High Energy Microcalorimeter
Silver, E., et al., 2002, AIP Conference Proceedings, Volume 605, 555.
Modest FocusingMultilayered Optics
Low Background Microcalorimeter
High Spectral Resolution
The folded scattering curve predicts a HEW of 34 arcsec for single reflection telescope made from this plastic.
Expected HEW if the telescope was built perfectly, i.e., there are no figure errors
The telescope needs to being nothing more than a “light bucket” with a HEW ~ 4 arcmin. work with the prototype conventional optic. (Schnopper et al. 2003)
Requirements can be easily met.
Thin Foil Plastic Optics
Tel
esco
pe E
ffect
ive
Are
a (c
m2 )
0
20
40
60
80
Energy (keV)20 30 40 50 60 70 80 90
Cou
nts
/ 10
eV B
in in
106
s
0
5
10
15
20
25
30
35
40
44Ti
Sn K EscapeLines From
44Ti
67.5 68.0 68.50
5
10
15
20
25
30
35
50 eVFWHM
Multilayer TelescopeBandpass
Modest focusing (<4 arc min), multilayered optics to reduce the background and enhance
the effective area in a balloon-borne experiment
A 20 x 20 array of microcalorimeters with 50 eV resolution
3 σ narrow line sensitivity at 68 keV is 3.3 a 10-7 ph cm-2 s-1 in 106 s; 50 times more sensitive
than INTEGRAL
Sufficient spatial and spectral resolution to determine the extent and the velocity distribution of the 44Ti emitting region
Non-X-ray background is almost 3 orders of magnitude less than typically achieved in this energy region
Recent Technical Advances
Microcalorimeters
Soft X-Ray detectors
Reduced readout noise
3 eV at 6 keV (60 mK)
Consistent with model calculations
Absorber
Thermistor
Heat Sink
AluminumWires
= C / GX-Ray
Tantalizing Outlook for high energies Earlier measurement (80 mK) 50 eV 30 eV
Use soft x-ray thermistor(60 mK) Larger R and dR/dT S/N increases
Larger volume x-ray absorbers may improve Q.E. 4-fold
This large spiral prototype lens is wound with seven turns of W coated PET plastic. Twenty-four ribs in the front and back wheels support a 50 mm wide, single strip of plastic. The pins are 1.27 mm in diameter and the spacing between the shells is 2 mm. A 6 in scale is placed in front of the lens.
Novel Conical Spiral for Astronomy Single Reflection (ε = 60%) 1.6 x Reflection efficiency of 2 reflections
X-ray Optics
Small Cylindrical Spiral Lenses
For the Laboratory
Potential Increase in Collecting Area
4-5 times (detector efficiency)
1.6 times (reflection)
6.4 – 8 (Total)
Flight Program
Test flight of optics in September 2005 aboard MSFC gondola
Seeking support to finish microcalorimeter array and electronics
To be incorporated in Ball Aerospace lightweight dewar
Cas A 20 days Fairbanks, Alaska
QED : Basis and cornerstone of all present field theoriesEnormous success in predicting properties of electrons in weak fields
However
A precise test is still pending for strong field limit where new phenomena may appear
Comparison of predictions and experimentally determined energy levels of strongly bound electrons provides a critical test of QED
GSI-Accelerator Facility
UNILAC
SIS
ESR 11.4 MeV/u U73+10 - 500
MeV/u U92+
up to 1000 MeV/u U92+
UNILAC
GAS JET
Ge(i)
90º
48º48º
132º
)cosθβ(1
EE
lab
projlab
γ
N Ion 108
1 10 20 30 40 50 60 70 80 90109
1010
1011
1012
1013
1014
1015
1016
1s<
E>
[V
/cm
]
Nuclear Charge, Z
1s-ground state: increase of the electric field strength by six orders of magnitude
Atomic Physics in Extremly Strong Coulomb Fields
Z = 92
H-like UraniumEK = -132 103 eV<E>= 1.8 1016 V/cm
HydrogenEK = -13.6 eV<E>= 1 1010 V/cm
Z = 1
Quantum Electro- Dynamics
Self Energy
Vacuum Polarization
The Structure of One-Electron Systems
2p3/2
2p1/2
Ly α1(E1)
Ly α2(E1)
QEDDirac
-34.1 keV
-34.2 keV
-131.8 keV
-132.2 keV
QED Corrections
∆E ~ Z4 / n3
Z: nuclear charge number
N: principal quantum number
Atomic systems at high Z Large relativistic effects on energy levels and transition rates (e.g. shell and subshell splitting)
Large QED corrections
Transition energies close to 100 keV
Current Status∆E (β) ∆E (fit) ∆E (geometry) Ly α1± 2.6 eV ± 9.7 eV ± 8.5 eV 102170.7 ± 3.2
Stöhlker et al. Phys. Rev, 85, 15, 2000
What can the microcalorimeter add?
A Self-Calibrating Measurement !Better Energy Resolution !
E proj = γ ( 1 – β cos Θlab ) E lab
Determined from the Balmer spectroscopy
of line energies known to 0.1 eV
Ultimately, precision can be 1 eV or better
Energy (keV)
0 10 20 30 40 50 60
Cou
nts
0
5
10
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25
Energy (keV)
0 10 20 30 40 50 60 70
Cou
nts
0
10
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30One Hour of Background Data With
Jet Target On But Microcalorimeters Blocked
First Operation of SAO Microcalorimeter at the GSI ESR
AM241 Calibration With the Jet Target On
X-Ray Studies for Au 78+
Commissioning of a Microcalorimeter at the ESR
Storage RingSilver, E., et al., 2003, Nuclear Instruments and Methods in Physics Research A 520, 60.
Spectrum obtained during parasitic beam time in March 2003
Microcalorimeter + EMI shield installed at ESR
Analysis
Au78+ 3d5/2 – 2p3/2 12.161 keV (rest)
Microcalorimeter 7.98 ± 0.01 keV
Doppler correction = 0.656 ± 0.0016
Scale Ly α1 escape @ 21.8 keV
after adding Sn Kα = 25.196 keV
46.99 keV (lab)
71.63 ± 0.106 keV (rest)
Note: Ly α1 corrected for QED = 71.570 keV (Beier et al. 1997)
Next Experimental Campaign
3 Detectors 16 detectors 5.3 x
520 mm 220 mm 5.6 x
145° 90° ; SA correction
0.652 0.8962 1.9 x
Total increase in rate 56.3 x
(SA 5 x 10 -8 sr 2.6 x 10 -6 sr)