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

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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

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5

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Energy (keV)

0 10 20 30 40 50 60 70

Cou

nts

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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)