Focusing gamma rays for sub-MeV astrophysics: state of the

Focusing gamma rays for sub-MeV astrophysics:state of the art of Laue lenses

Nicolas Barrière, Lorenzo NatalucciINAF - IASF Roma

ESAC - Madrid - March 26th 2009

N. Barrière - ESAC Seminar - 03/26/2009

Outlines

! Introduction! Interests of the sub-MeV gamma-ray astrophysics! Laue lens: why and how?! The Gamma Ray Imager - performances

! Laue lens state of the art! Theoretical and experimental study of crystals for a Laue lens! Still challenging: accurate orientation of crystals! Laue lens design study: general considerations

! Current projects! Laue lens + Compton telescope! A techno-scientific balloon borne mission to pave the way?

! Conclusion


Soft gamma rays and associated science themes

! Gamma rays probe non-thermal processes

! Particle acceleration, particle interactions, nuclear physics

! Gamma rays are penetrating

! Probe deep in the central engine, e.g. Supernovae or compact objects

! Gamma rays are produced in a large diversity of emission sites

! Sun, Compact binaries, pulsars, SNR, Galaxy/ISM, AGNs, GRBs, CB

Pulsars SNR AGN - µQSO

SN

NovaeSN

Physics of supernovae, Novae, Xand gamma ray bursts

Physics of pulsars, compact objects,supernova remnants, Sun

Cosmic explosions Cosmic accelerator


Type 1a Supernova explosion mechanism?

Commonly accepted scenario,But what is the physics behind?

SN1998bu (Gorgie et al. 2002)

847 keV line light curve (11.3 Mpc)847 keV line profile (1Mpc, 120 days after explosion)

(Gòmez-Gomar et al. 1998)

Comptel

1) Standard candles: characterize the 56Ni production, relation to optical2) Explosion physics: uniquely distinguish explosion physics3) Variety: Origin of the intrinsic variety (sub-super luminous)


Origin of Galactic positrons?

Jean et al., 2006

Weidenspointner et al. 2008

Spectroscopy of emission coming from the bulge:! Positrons annihilates in the warm and partiallyionized phase

Unique spatial distribution…

Bulge: - Unresolved point sources? (LMXBs??, microquasar??) - Central black hole (Sgr A*) + diffusion?

Disk: - Combination of LMXBs + 26Al & 44Ti

! Need for more sensitivity, spectroscopy, and better angular resolution


Origin of the soft gamma-ray cosmic background radiation?

! Cut-off distribution of accretion-dominated AGNs! Fraction of Compton thick sources among obscured AGN! Contribution of blazars with breaks in MeV regime! ++ AGN physics and geometry probed through polarization measurement

[Comastri et al, 1999]

Blazar?

AGN, resolved in X-rays

Blazar


Sensitivity of gamma-ray telescopes

Nuclearastrophysicsdomain

Energy (MeV)

Courtesy: S. Boggs


Principle of existing gamma-ray telescopes

! Aim:! Determine the original incidence

direction! Spectroscopy

!

n" =S

S + N#

S

N$

S

Vdet

Detection significance:

! Sensitivity only increases

as the square root of the

detector's surface

Aperturemodulation

Comptonkinematics

! Problem:!Very intense instrumental background!Sources fluxes are weak


Alternative solution

! Depth-graded multilayers mirrors [Jensen et al., 2007]

! Outstanding imaging capabilities

! Emax !300 keV (today Emax = 80 keV)

! Phase Fresnel lens [Skinner, 2005]

! Chromatic

! Very long focal length 106 km (500 keV)

! Laue lens

! How to make a sizeable sensitivity leap in the softgamma ray domain?! Decoupling the sensitive area from the collecting area


Laue lens principle

!

dhkl

!

T0

!

"B

!

"B

! Based on Bragg diffraction in the volume of crystals: Laue Geometry

! Crystal slabs arranged on concentric rings: Photons are diffractedfrom every ring towards a common focal point

! Beam deviated of 2 "B ! long focal length: - Formation flying

- Extensible boom

Small angle of deviation= conservation of thepolarisation of incident radiation

!

!

2 dhkl

sin"B

= n #

[Curado da Silva et al.,IEEE 2007]

Experimentally confirmed


Broad band Laue lens

! Same crystal using same reflexion on several adjacent rings

! diffracted wavelength is shifted from one ring to another

1234

Energie

Su

rfa

ce

eff

ica

ce 4

"1#

1

"2

"3

"4

#2

#3

#4

f

3

2

1

# variable

dhkl constant

MAX GRI


Narrow band Laue lens: CLAIRE

[Halloin, 2003; von Ballmoos et al., 2004]

Surf

ace e

ffic

ace (

cm

2)

Energie (keV)170 175165160

0

10

20

30

!

dhkl

sin"B

= const # dhkl,i

ri= const $i

! Example of the CLAIRE lens built at CESR (Toulouse,France) in 2001

! 556 Ge1-xSix crystals focusing at 170 keV

! 8 rings:

Ge (111) (220) (311) (400) (331) (422) (333) (440)

# constant

dhkl variable4

"1#

1

"2

"3

"4

#2

#3

#4

f

3

2

1


The Gamma Ray Imager

! 100m focal distance ! Composed of 2 satellites flying in formation

! Optics spacecraft:! Grazing incidence mirrors (simple reflection): 20 keV - 300 keV! Laue lens: 220 keV - 1300 keV

! Detectors spacecraft:! Option 1: CZT pixellated detector! Option 2: Stack of stripped planar germanium detectors

[Knödlseder et al, (2006; 2007)]

http://gri.iasf-roma.inaf.it


Example of lens conception: GRI

Rayon (

cm

)

Energie (keV)


GRI: Effective area

• Crystals mass: 250 kg• Crystals: Cu: 18465; Si: 7757; Ge: 1315• Mosaicity: 26 - 40 arcsec

• Radii: 65.50 cm - 179.80 cm• Crystals' size: 10.0 - 15.0 mm• Geometrical area: 27537 cm2

• Lens' structure: 1.5 mm eq. Al

Surf

ace e

ffic

ace (

cm

2) Point source on-axis


GRI's sensitivity

[knödlseder et al., 2007]


Imaging? Point source off-axis PSF

55% in Ø 24 mm

15 arcsec

30 arcsec

60 arcsec

90 arcsec

120 arcsec

150 arcsec

GRI:Angular resolution: 30 arcsecField of view: 5 arcmin FWHM


Outlines




! Conclusion


Definitions

! Rocking curve: Plot of the intensity (diffracted or transmitted) whilethe crystal is rotated in a parallel and monochromatic beam

! Diffraction efficiency: Ratio of the diffracted intensity over thetransmitted intensity

! Reflectivity: Ratio of the diffracted intensity over the incidentintensity => includes the absorption

!

dhkl!

T0

!

"B

!

2"B

Incidentbeam

Diffractedbeam

Transmittedbeam

Crystals characterization:Rocking curve

Angle d'incidence

!

"B

Laue geometry of diffraction


Getting a bandpass diffracted: Mosaic crystals

! Juxtaposition of tiny perfect crystal blocks (the crystallites)slightly disoriented the ones with respect to the others (Darwinmodel)

! Gaussian angular distribution of crystallites which FWHM is called'mosaïcity' $

" Gaussian energy bandpass

# Gaussian profile of the diffracted beam

! mosaic difocusing

# Diffraction efficiency ! 50 %

" As-grown mosaic structure for alot of different crystals :

- Copper- Silver- GaAs- Gold- …

Meanorientation

t0 T0

[Darwin, 1914; 1922]


Mosaic crystals

Ø 80 mm

180 m

m

Cu (ILL, Grenoble, France)Au (Mateck Gmbh)

Rh & Ag (Mateck)

GaAs (IMEM, Parme, Italy)

Cellular structure asrevealed by DSLetching in GaAs

[Ferrari et al, 2008]

[Courtois et al., 2005]


Alternative solution: crystals with curved diffracting plans

! Qualitative view: assembly of fine slices disposed in 'fan'

! Rectangular-shaped angular distribution of crystalline plans

d

$ Rectangular shaped energy bandpass

" rectangular shaped diffracted beam

profile

! Better focusing

" Diffraction efficiency ! 100 %

# Hard to obtain such crystals- Temperature gradient- Elastic bending- Concentration gardient

d: distance over which the orientation of plans vary from more than a Darwin Width

[Smither et al. 2001; Malgrange et al., 2002]


Crystals with curved diffracting plans

Curved

diffractingplanes

Ge c

oncentr

ation

Example: Si1-xGex, x increasingalong the growth axis

Composition gradient crystal Elastic bending by surface treatment

Example: Si wafer curved by grooves


Search of efficient diffracting materials

1) Calculate the reflectivity of various potentially interesting materialsª Available in large quantities,ª not toxic, radioactive, too expensiveª (melting point under 3000 K)ª Relatively good crystal quality mosaicity around a few arcmin

2) Find crystal producers, and get some representative samples

3) X-ray diffraction:! Measure the actual mosaicity, check the homogeneity and of the

selected samples! Calculate reflectivity and check the accordance with theoretical

predictions


What are the best materials?

Increasing mean Z

Hypothesis:- Mosaic crystals- Mosaicity = 30 arcsec- Thickness optimized

but " 2 mm- Kinematical theory of

diffraction

Scope of the theoretical study:- every pure-element crystal satisfying Laue lens requirements- a selection of 'commonly produced' two-component crystals

[Barriere et al., 2009]


ESRF & ILL: High-energy X- and gamma-ray beams

ILL: GAMS(184 keV < E < 2 MeV)ESRF: beamline ID 15A

(100 keV < E < 750 keV)

Cu

Ge

SiGe

Ag

Au

Pt

Pb

Rh

GaAs

InP

Al2O3

CaF2

CdTe

Crystals investigated / developped since 2005:

Grenoble, France

Accretion physics

Cosmic explosions


% 100 keV # E # 750 keV (tuneable)

% Beam cross section: from 10 x 10 µm2 up to 4 x 4 mm2

% Beam div. = < 1 arcsec

ESRF experimental setup

"B

Monochromators:

2 bent Ge (711)

SlitsBeam stop

Collimators:

2 tunable slits

Ge detector

Diffracte

d beam

Detector in transmitted beam

position

Sample on its

rotation tower

Experimental hutch

57.5 m 1.89 m 1.19 m1.775 m

White

beam

Optical hutch

&x

y

z


ESRF, beamline ID15A experimental Setup

Crystal

Ge

detector

Cryostat for

Ge det


Experimental results: "Well known" crystals

E = 589 keV Copper mosaic crystal(produced by ILL, Grenoble, France)

8.6 mm thick => Reflectivity = 0.24

Today: ' Crystal quality

' Mosaicity range' Reproducibility

( Cutting procedure

! We are confident

Si1-xGex gradient crystal(produced by IKZ, Berlin, Germany)

23 mm thick => Reflectivity = 0.26

E = 299 keV

' First time with large ingots

' First time that "mosaicity" reaches30 arcsec

! Development still ongoing, very

successful so far

FWHM =30 arcsec

FWHM =15 arcsec

[Barrière et al. 2007; 2009]


Experimental results: "New" promising materials

E = 589 keVGold mosaic crystal

(produced by Mateck, Germany)


Very promising results

Firsts attempts with 3 pieces:

' 10 arcsec < mosaicity < 60 arcsec

' Reflectivity > 30% at E > 500 keV

E = 184 keV Silver mosaic crystal(produced by Mateck, Germany)


Very promising results

First attempt with 1 pieces:

' Mosaicity range! Need to be investigated at higher energy

FWHM =16 arcsec

FWHM =

50 arcsec


Laue lens prototypes

[von Ballmoos et al., ExpA 2008] [Frontera et al., SPIE 2008]

• 556 Ge mosaic crystals• Ground tests, 2 balloons flights ! Crab nebula detection

20 Cu mosaic crystalsglued on a carbon fibersupport

• Setup of an assembling and testing facility• Development of a mounting method without

orienting device ! High packing factor

20072001


Main issue: orientation precision

! Problems:! most of crystals does not cleave (split along diffracting plans)! Some of them are too smooth to be polished => not possible to

make a plan of reference)

! Crystals cutting precision is about 2 arcmin! Good enough for two angles but not for Bragg's Angle! no external reference for Bragg's angle

! Crystals have to be oriented in an X-ray beam

%x

%*

%x


Crystals orientation: CLAIRE's method


Current R&D in France (CNES Founded, CESR + TAS)

2nd step: Eachcrystal has itsdedicated spot, withpins machined to setthe diffracting planesat the rightorientation

Aluminium unit cellwith 3 accuratemachined pins foreach crystal

3 pins

%x1st step: Characterization of the assymetryangle with respect to a reference surface onthe crystal

Prototype due for the end of 2009


Current R&D in Itaty (Univ. of Ferrara, ASI Founded)

Courtesy: F. Frontera

First try

Accuracy around 1.5 arcmin

Error budget analysis

1) Orientation of crystals: 2 pins are glued to keep theorientation for the crystal assembly2) Pins are inserted in a counter mask, which holes havebeen drilled at the Bragg angle3) Counter mask is put on the lens frame and crystals areglued4) Pins are chemically separated, and counter maskremoved.

New prototype for summer 2009


Lens design: Factor of merit definition

! Most important criterion? Sensitivity!

!

fn =n N

c1X=

n b "E h (1+#)

1+# $#

%sf

&

' ( (

)

* + + %det%S tobs

Aon

Al%sf

!

" =Aon

Aoff

For an off-axis source, the focal spot issymmetrical:

!

Aon

Al"sf#

rPSF

Signalin

A unique criterion for the optimization of every parameter:mosaicity, size of crystals, focal distance, materials, …

PSF must be computed fastly to be able to test a large range of parameters

GRI: PSF for a point source on axis

Ropt = 12 mm

&sf = 0.55

!

"

"r

Sin

rPSF

#

$ %

&

' ( = 0 ) FM =

Sin

rPSF

#

$ %

&

' (

max


Simulation parameters:• Cu 111• Fixed energy band: 500-530 keV

Lens design: focal distance, mosaicity, and disorientation

Ideal orientation Disorientation: ' = 30 arcsec

Factor of merit

• Gaussian angular distribution of crystals orientation• Crystals: 15 x 15 mm2


Lens design study: Mosaicity, Size of Crystals, disorientation

Focal length = 20 mIdeal orientation Disorientation: ' = 30 arcsec

Simulation parameters:• Cu 111• Fixed energy band: 300-400 keV

• Gaussian angular distribution of crystals orientation• Focal distance = 20 m

Factor of merit


Outlines




! Conclusion


New mission concept: associate a Laue lens to wide fieldCompton telescope: DUAL

+ point source sensitivity+ High angular resolution(+ polarisation)- Narrow field of view- Narrow energy band- Small number of targets

+ Large number of targets+ Survey sensitivity+ Polarisation- Feasibility (ACT class)- Angular resolution- SN sensitivity

2 complementarytelescopes:

AGNLMXBs (e+ e-?)PulsarsSN

e+ e- (galactic center)26Al60Fe

Point source

Extended sources

Peter von Ballmoos, Tad Takahashi, Steven Boggs


R&D for compact Compton telescopes (examples!)

NCT developped at SSL (Berkeley, USA)

HPGe stripped planar detectors

Developped at ISAS / JAXA (Tokyo, Japan)


DUAL lens design: an interesting option

Based on newly discovered crystals

F = 20 m : extensible boom

Composed of 20100 crystals tiles, 15x15 mm2, mosaicity = 2 arcmin! Relaxed requirements on orientation

Crystals mass: 165 kgColecting area: 4.5 m2

Total lens mass ~ 550 kg


DUAL Laue lens' telescope sensitivity

Low earth orbit, equatorialCZT focal planCompton background rejection Courtesy: L. Natalucci


10m focal length lens for a balloon fligth

Study of e+-e- annihilation line from a balloon borne mission

Focal length = 10 mObjective: - Scan a handful of potential sites of positrons annihilation

- Scientifically exploitable Laue lens demonstrator

Performance summary• Energy range 500 - 520 keV• FoV 12 arcmin• Angular resolution 1 arcmin• Sensitivity: 7x10-6 ph/s/cm2 (3', Tobs 10 ks)

Lens• Crystals: Ge, Cu, Rh, Ag, W• 8x8mm2, 3000 pieces ! 15 kg• 70 cm in diameter

50 times better than INTEGRAL/SPI

150 cm2

concentratedin 1 cm2

6 cmEff

ecti

ve a

rea (

cm

2)

Energy (keV)


Conclusion

With the GRI mission, we established how a focusing telescope could answer

some of the most fundamental questions of modern high energy astrophysics,

thanks to:

• Unprecedented sensitivity in the energy range 200 keV - 1 MeV

• Polarisation measurement (pixellated focal plane + Compton reconstruction)

• (Poor) imaging capabilities

GRI is not going ahead, but the principle of a gamma-ray focusing telescope

remains the only option to increase dramatically the sensitivity in the soft

gamma-ray domain

Thanks to the support from French, Italian and European space agencies,

technological issues are being overcome:

• French and Italian prototype ready in a few months

• Crystals study and development (crystal growth, cutting, gluing)

Documents

Focusing gamma rays for sub-MeV astrophysics: state of the