F. Frontera

Uinversità di Ferrara

Extending the passband of focusing Extending the passband of focusing hard X-ray telescopes beyond 80 keV: hard X-ray telescopes beyond 80 keV:

science motivations and prospectsscience motivations and prospects

AGN9 Ferrara, 24-27 June 2010

Collaboratori

• Enrico Virgilli, Gianluca Loffredo, Marco Statera, UNIFE

• Vito Carassiti, Federico Evangelisti, Stefano Squerzanti, INFN, sezione di Ferrara

• Ezio Caroli, John Stephen, INAF/IASF, Bologna

Introduction• BeppoSAX has shown that, in order to understand

the physics underlying many classes of galactic and extragalactic sources, two main requirements on the instrumentation are resulted to be crucial:– Broad energy band (from fraction of keV to hundreds of

keV)– High flux sensitivity on time scales as short as possible

(source variability time scales) • The only way to meet both requirements is to use

focusing telescopes that cover the broadest energy band:– Low energy (0.1-10 keV) telescopes are well tested;– Medium X-ray energy band (up to 70-80 keV) telescopes

are being tested in space with NUSTAR, ASTRO-H– High energy X-ray band (>70/100 keV) telescopes are in

an advanced stage of development.

Some issues that can be settled with soft γ-ray observations (70/100-600 keV)

– Physics in the presence of super-strong magnetic fields (magnetars);

– Precise role of the Inverse Compton in cosmic sources (e.g., AGN);

– Precise role of non-thermal mechanisms in extended objects (e.g., Galaxy Clusters);

– Origin and distribution of high energy cut-offs in AGNs spectra;

– Origin of Cosmic X-ray diffuse background (CXB).

– Determination of the antimatter production processes and its origin.

High-energy spectra of magnetars

Goetz et al. 2006

XMM and INTEGRAL spectra of magnetars:different behaviour of SGRs and AXPs.

A better sensitivity at E>100 keV is required to fix the origin of the high

energy component

4U 0142+61 (Kuiper et al. 2006)

• Relative size of– Unabsorbed (logNH<21.5)– Compton-thin

(21.5<logNH<24.5)– Compton-thick (logNH>25) RQ

populations;– Blazars (RL)

• Distribution of power-law indices of each population;

• Distribution of high energy cut-offs of each radio quiet population;

• Luminosity function of each population with energy.

• In the case of blazars, the gamma–ray observations are crucial given that their energy emission peaks at hundreds of keV.

AGNs (RQ, RL) open issues

Gilli et al. 2007

Cutoff energies vs. Gamma

Perola et al. 2002

Sample of 8 BSAX Seyfert 1

Cut-off energies fix the energy of the accelerated electrons Cut-off energies fix the energy of the accelerated electrons that Comptonize the low energy seed photons and give info that Comptonize the low energy seed photons and give info about the mass accretion rate. about the mass accretion rate. A much better sensitivity is needed to measure them for A much better sensitivity is needed to measure them for a larger sample of RQ-AGN population.a larger sample of RQ-AGN population.

XTE 1650-564 Outburst 1998

Cutoff energies vs. Gamma (or NBMC)

In the case of Galactic BH in LMXBs, the cutoff energy give In the case of Galactic BH in LMXBs, the cutoff energy give information on the mass accretion rate and bulk motion information on the mass accretion rate and bulk motion Comptonization (see L. Titarchuk talk) Comptonization (see L. Titarchuk talk)

XTE 1650-564 Outburst 1998

Titarchuk and Shaposhnikov 2010

Cosmic X-ray background and AGN synthesis modelsCurrently, a combination of unobscured, Compton thin and Compton thick RQ-AGN populations with different scatter in the photon index distribution and fixed EF are assumed in synthesis models of CXB (Gilli et al. 2007) up to 100 keV. Is it right to assume a fixed EF ? Which is the real contribution to CXB from RL-AGNs?Measurements beyond 100 keV of a large sample of AGNs of different populations are crucial.

Gilli et al. 2007

RQ-AGNs

Comastri et al. 2005

RL-AGNs

• Significant results show that hard tails of GC exist (Rephaeli et al. 2008);

• Which is their origin?– Are they the result of a

diffuse emission or due to AGNs in the GC?

– In the former case, which is the emission mechanism?

• Which is their contribution to CXB?

• Much more sensitive observations are crucial up to few hundreds keV.

Hard Tails of Galaxy Clusters

Coma Cluster

Fusco-Femiano et al.2007

• Positron production occurs in a variety of cosmic explosion and acceleration sites.

• Observation of the 511 keV annihilation line is a powerful tool to probe plasma properties.

• Claim for an annihilation line from a compact source (Nova Muscae) reported and never confirmed;

• Diffuse annihilation line emission found with INTEGRAL, whose origin is still unknown;

• Search of 511 keV lines in compact sources requires much more sensitivity.

Positron astrophysics

Weidenspointner et al.

2008

Goldwurm et al.1992

Requirements for high energy telescopes:

– Continuum sensitivity two-three orders of magnitude better than INTEGRAL at the same energies (goal: a few x10-8 ph/(cm2 s keV in 106 s, ΔE=0.5 E).

– much better (≤ arcmin) imaging capability

High energy (70/100 keV) telescopes: High energy (70/100 keV) telescopes: Laue lensesLaue lenses

• Ongoing developments in Europe

– Narrow band (800-900 keV) Laue lenses for nuclear astrophysics, at CESR Institute, Toulouse;

– Broad band Laue lenses (70/100-600 keV) at Physics Dept, University of Ferrara.

– in Dublin (Ireland) for medical applications.

• Main issues that are being solved:– Developing a technology for assembling

thousands of crystals;– Developing a technology for a massive

production of proper crystals.

Activity UNIFE: First lens prototype 1/2

Mosaic crystals of Cu[111]

Tile size: 15x15x2 mm3

Mosaic spread: 3/4 arcmin

Lens support: carbon fiber

Frontera et al. 2008

First lens prototype 2/2

Difference between measured image and Monte Carlo image in the case of a perfect assembling of the crystals in the lens

Improved lens prototype: under development

In addition: LAUE project (main contractor DTM) already started.

Crystal development status• Mosaic crystals made of

Cu are currently produced by ILL

• Mosaic crystals of Ge have been developed by IKZ, Berlin.

• Mosaic crystals are also being developed by CNR, IMEM, Parma, Italy;

• Also available commercial crystals (e.g., Mateck Gmbh (samples of Ag, Rh already tested).

• Bent crystals (by indentation) are being developed by LSS, University of Ferrara

Measured reflectivity of a curved Si(111) @ 150 keV

Effective area of the lensMosaic crystal

distribution in the lens rings

Study of a 20m FL Laue lens made of mosaic crystals (Barriere et al. 2009)

Continuum sensitivity in 105 s

Assumed BKG (LEO)

Curved crystals vs. flat crystals

10 m FL 20 m FL

Conclusions

• A big effort has already been performed and is still in progress for the development of focusing Laue lenses

• Laue lenses with low focal length (10--15 m) are already feasible.

• The development of curved crystals improves sensitivity and angular resolution by about a further order of magnitude with respect to Laue lenses with mosaic crystals.

• A project "LAUE", supported by ASI, has just started – for the massive production of both curved crystals;– a more accurate assembly technology .

• No need of high focal lengths (>20 m) for extending the band up to 600 keV

• An energy passband up to 300 keV can be easily obtained with 10 m focal length.

• Concrete prospects for a broad band satellite mission with both multilayer mirrors and Laue lenses from a fraction of keV to several hundreds of keV.