Laue lenses for hard X-rays (> 60 keV)

F. Frontera and A. Pisa

on behalf of

a Large Collaboration

Rome, 18 March 2005

Participants to the project

• Physics Dept, University of Ferrara• IASF/INAF, Bologna• Institute Laue-Langevin (ILL), Grenoble

Origins

Status of the high energy X-ray (>60 keV) observations

• Energy spectra beyond 60 keV are now well determined only for the hardest and strongest sources in the sky.

• For most sources, above 70-80 keV the spectra are scarcely known (see examples).

• However the >60 keV channel is crucial for several scientific objectives.

Cygnus X-1 (one of the strongest sources) observed with BeppoSAX

In hard/low state In soft/high state

From Galactic to extragalactic X-ray sources

AGNs: High energy cut-offundeterminedX-ray pulsars: High energy spectrum too

weak for current instrument sensitivities

The 60-300/600 keV range is crucial for several scientific objectives:

a. to study physics of in presence of super-strong magnetic fields (Mass accreting X-ray pulsars, Anomalous X-ray Pulsars).

b. to study radiation processes in Gamma Ray Bursts (role of Inverse Compton with respect to synchrotron or thermal processes).

c. to study the role of non thermal mechanisms in extended objects (Supernova Remnants, Galaxy Clusters).

d. to access nuclear (e.g., 44Ti) and/possibly, annihilation lines.

e. to study the high energy cut-offs in the spectra of Active Galactic Nuclei.

f. to establish the origin of the high energy Cosmic X-ray Background (see viewgraph).

Origin of Cosmic X-ray Backgound (CXB)

• In the 2-5 keV range, a large fraction (about 80%) of the CXB is resolved into discrete sources.

• In the 5-10 keV range, 50% of the CXB is still unresolved.

• Above 10 keV, the origin of all CXB flux is an open issue.

• If the CXB due to discrete sources, a class of sources with a spectral roll-over with an e-folding energy of 100-300 keV is required.

• A new population or not?

Short dashed : unabsorbedLong dashed : Compton thinSolid : Total

Blue lines : high energy cutoff at 400 keV

Red lines: high energyCutoff at 100 keV

Model parameters tuned To account for 80% of the XMM (2-10 keV) background with the“observed” NH distributionNo Compton thick and onlyA fraction of the more Obscured (logNH > 23) Compton thin

From Comastri 2004

How to improve instrument sensitivity at E>10 keV

• Focusing optics based on multilayers or traditional X-ray optics with high focal lengths (>30 m) can improve the flux sensitivity up to 60/70 keV.

• Above 70 keV, the best candidate technique appears the Bragg diffraction from mosaic crystals in transmission configuration (Laue lenses).

• Our HAXTEL (= HArd X-ray TELescope) project: to develop a Laue lens with a passband from 60 to 300/600 keV.

A Laue lens for hard X-rays: main properties

• Technique: Bragg diffraction from mosaic crystals;

• Geometrical configuration: spherical (sphere radius = 2 times the focal length FL);

• Crystal element size: as small as possible (if flat);

• Among the critical tasks: to give the right orientation to each crystal of the lens;

• Among the best candidate materials: Cu (111)

Distribution of the crystal tiles; Dependence of the lens size on focal length.

Optimization criteria

• For a given crystal material, the effective area and sensitivity can be optimized with a proper:– Crystal thickness vs. Energy;– Mosaic spread;– Focal length;– Size of crystal tiles.

Examples of Cu (111) reflectivity test results at about 100 keV

Examples of Cu (111) reflectivity test results at about 100 keV

Status of the development project

• Under way: Development of a demonstration model (DM) with 30 crystals 15x15 mm2.

• Next step: Development of the prototype model with 500 crystals.

Prototype Model

• Energy passband: 60-200 keV;

• Inner radius: 6 cm• External radius: 21 cm• FL = 210 cm• Crystal element size:

15x15 mm2 • Crystal thickness: 2 mm

(for 350 crystals), 4 mm (150 crystals)

• Tests with the LARIX facility in Ferrara.

Multi-lens telescope concept (1-300/600 keV)

• Assumed configuration:– 1 Wolter I focusing optics– 4 high energy (150-600 keV)

lenses (HE);– 1 low energy (54-400 keV) lens

(LE);– 10 and 15 m focal length.

Multi-lens configuration

LE

HE

ML

Multi-lens sensitivity (106 s)

10 m focal length 15 m focal length

For comparison: Simbol –X (30 m FL)

LARIX facility project for calibration of hard X—ray/gamma-ray mirrors/lenses

• Main features:

a. Operative energy band: 40-400 keV;

b. Beam line length: 100 m (under ground)

b. Beam line diameter: 60 cm

c. Large mirror chamber with mechanical manipulators;

d. Focal plane detector chamber at variable distance from the mirror chamber;

e. Clean room.

View of the Ferrara tunnel for the X-ray beam line