FOCUSING OPTICS WITH MOSAIC CRYSTALS

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Extending the passband of focusing hard X-ray
telescopes beyond 80 keV science motivations and
prospects
F. Frontera Uinversità di Ferrara
AGN9 Ferrara, 24-27 June 2010
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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

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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 (gt70/100 keV) telescopes
  are in an advanced stage of development.

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Some issues that can be settled with soft ?-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.

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High-energy spectra of magnetars
XMM and INTEGRAL spectra of magnetars different
behaviour of SGRs and AXPs. A better sensitivity
at Egt100 keV is required to fix the origin of the
high energy component
4U 014261 (Kuiper et al. 2006)?
Goetz et al. 2006
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AGNs (RQ, RL) open issues

• Relative size of
• Unabsorbed (logNHlt21.5)
• Compton-thin (21.5ltlogNHlt24.5)
• Compton-thick (logNHgt25) 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 gammaray
  observations are crucial given that their energy
  emission peaks at hundreds of keV.

Gilli et al. 2007
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Cutoff energies vs. Gamma
Perola et al. 2002
XTE 1650-564 Outburst 1998
Sample of 8 BSAX Seyfert 1
Cut-off energies fix the energy of the
accelerated electrons that Comptonize the low
energy seed photons and give info about the mass
accretion rate. A much better sensitivity is
needed to measure them for a larger sample of
RQ-AGN population.
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Cutoff energies vs. Gamma (or NBMC)
XTE 1650-564 Outburst 1998
Titarchuk and Shaposhnikov 2010
In the case of Galactic BH in LMXBs, the cutoff
energy give information on the mass accretion
rate and bulk motion Comptonization (see L.
Titarchuk talk)
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Cosmic X-ray background and AGN synthesis models
Currently, 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.
RQ-AGNs
RL-AGNs
Gilli et al. 2007
Comastri et al. 2005
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Hard Tails of Galaxy Clusters

• 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.

Coma Cluster
Fusco-Femiano et al.2007
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Positron astrophysics

• 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.

Goldwurm et al.1992
Weidenspointner et al. 2008
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• 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, ?E0.5 E).
• much better ( arcmin) imaging capability

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High energy (70/100 keV) telescopes Laue lenses
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• 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.

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Activity UNIFE First lens prototype 1/2

• Mosaic crystals of Cu111
• Tile size 15x15x2 mm3
• Mosaic spread 3/4 arcmin
• Lens support carbon fiber

Frontera et al. 2008
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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
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Improved lens prototype under development

In addition LAUE project (main contractor DTM)
already started.
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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) _at_ 150
keV
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Study of a 20m FL Laue lens made of mosaic
crystals (Barriere et al. 2009)
Mosaic crystal distribution in the lens rings
Effective area of the lens
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Assumed BKG (LEO)
Continuum sensitivity in 105 s
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Curved crystals vs. flat crystals
10 m FL
20 m FL
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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 (gt20 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.