Transcript FOCUSING OPTICS WITH MOSAIC CRYSTALS

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
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
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
Goetz et al. 2006
4U 0142+61 (Kuiper et al. 2006)
AGNs (RQ, RL) open issues
• 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 cutoffs 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.
Gilli et al. 2007
Cutoff energies vs. Gamma
Perola et al. 2002
Sample of 8 BSAX Seyfert 1
XTE 1650-564 Outburst 1998
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.
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)
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
Hard Tails of Galaxy Clusters
• Significant results show
that hard tails of GC exist
(Rephaeli et al. 2008);
• Which is their origin?
Coma Cluster
– 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.
Fusco-Femiano et al.2007
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
Weidenspoint
ner et al.
2008
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:
Laue 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
Frontera et al. 2008
 Lens support: carbon fiber
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
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
Assumed BKG
(LEO)
Continuum sensitivity in 105 s
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.