Diapositiva 1

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Cluster of galaxies and large area survey
Wide-field X-ray telescopes
Sergio Campana INAF - Osservatorio Astronomico
di Brera/INAF - Via Bianchi 46 23807 Merate
(Lc) Italy
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Outline

• Dark energy probe needs for a large area survey
  
• Wide-field X-ray polynomial optics for imaging
  applications short review of the concept

Mainly based on Panoram-X proposal and NASA white
papers (Haiman et al. 2005 and Vikhlinin et al.
2005) and final JDEM proposal (Bautz et al. 2006).
but
I am not an expert in clusters of galaxies and
large scale structures
I am not an expert in mirror manufacturing
so I will try to be short
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Why is the universe expansion accelerating?
What is DE made of? (73 of our universe is made
of DE!)
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Probes
Now Future CMB WMAP Planck Supernovae
HST SNAP Clusters of galaxies X-ray
satellites ??
Cluster of galaxies Dedicated
survey?
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Cluster power spectrum and X-ray luminosity
function (Schuecker et al. 2003 Boehringer 2006)
Evolution of the cluster temperature (Henry 2004)
COMPLEMENTARY APPROACHES
Constan-cy of the cluster baryon fraction (Allen
et al. 2004)
Evolution of the cluster gas mass (Vikhlinin et
al. 2003 2006)
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Cluster Survey 105 clusters
Need to study the brightest fraction of clusters
to calibrate relations
Constrain the equation of state of Dark Energy,
(i.e. understand what is it!)
w(z)w0 wa z/(1z)
Better than high-z SNe or weak lensing surveys
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Cluster survey in context
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Survey simulated image
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Point-source limit
Side products X-ray background AGN
studies Starts in our Galaxy Cataclismic variables
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What do we need? Theory
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What do we need? Practice
Field of view 1.4 square degrees Orbit
efficiency 70 Vignetting efficiency 70
Survey area 10-20,000 square degrees
(slowly drifting satellite) Extended source
detection 30-50 counts Allocated time 9-12
months Flux limit for ext. sources 2-5
x10-14 erg cm-2 s-1
7-14,000 pointings
MINIMAL REQUIRMENTS Area 10,000 square
degrees Extended source detection 30
counts Allocated time 9 months Flux limit
for ext. sources 5 x10-14 erg cm-2 s-1
Need 1,825 cm2
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What about angular resolution
Concerning clusters of galaxies 15 arcsec HEW
(over the entire field of view) are
enough but for survey purposes the lower the
better (Goal 5 arcsec HEW over the entire field
of view)
How can we obtain these features?
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X-ray optics with polynomial profile

• Mirrors are usually built in the Wolter I
  (paraboloid-hyperboloid) configuration which
  provides, in principle, perfect on-axis images.
• This design exhibits no spherical aberration
  on-axis but suffers from field curvature, coma
  and astigmatism, which make the angular
  resolution to degrade rapidly with increasing
  off-axis angles.
• More general mirror designs than Wolter's exist
  in which the primary and secondary mirror
  surfaces are expanded as a power series.
• These polynomial solutions are well suited for
  optimization purposes, which may be used to
  increase the angular resolution at large off-axis
  positions, degrading the on-axis performances
  (Burrows, Burgh and Giacconi 1992)
• A trade-off of the whole optics assembly of a
  wide-field telescope can further on increase the
  imaging capabilities off-axis of wide-field
  polynomial optics

The wide-field polynomial optics concept was
extensively studied as a part of the WFXT
mission concept (OAB, CfA, Univ. of Leicester)
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Some historical remarks on WFXT-like missions

• 1992, Burrows, Burg and Giacconi investgate the
  possibility of using polinomial mirror
  configurations to get X-ray optics with a
  corrected PSF onto a large FOV
• 1995 WFXT small satellite proposal to NASA (PI
  R. Burg, J. Hopkins Univ, CfA, OAB)
• 1997-98 WFXT proposal and Phase A to ASI in the
  context of the small satellites program (PI G.
  Chincarini, OAB large part of the Italian AE
  community, CfA, Leicester Univ.)
• 2000 Panoram-X mission proposal to ESA in the
  context of the F2-F3 program
• 2001 Conconi Campana paper (AA 2001)
  improving mirror design
• 2003 ASTER-X concept (OAB in collaboration with
  NASA/GSFC) in view of the probe-Einstein program
  (never started), further mirror design improvement

• 2005 NASA Call for white papers on Dark Energy
  exploration two proposal based on the Panoram-X
  concept also ESA mention in the Cosmic Vision
  booklet the need of a similar mission, merged
  into a single proposal DECS (PI Bautz/MIT
  including OAB scientists).

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WFXT (ASI feasibility study 1997-1998)
Polynomial mirrors
WFXT (epoxy replication on SiC carrier) Ø 60
cm Focal Lenght 300 cm HEW 10 arcsec
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The Panoram-X mission

• proposed to ESA in 2001 in the context of the
  F2-F3 Mission Program
• in practice, it is the same WFXT concept scaled
  up in FL (3.5 vs. 3 m) and of mirror shells (50
  vs. 24)
• SiC mirror shells with diameter ranging from 70
  to 21 cm, total mirror height of 28 cm and max
  wall thickness 1 mm. Predicted HEW of 10 arcsec
  over a field radius of 30 arcmin (including
  profile and integration errors)
• X-ray camera made of an array of nine CCDs
  arranged in an inverted pyramid that matches the
  focal surface of the mirrors. Each device is a
  600x600 pixel front side illuminated frame store
  with pixel size 40 ?m corresponding to 2.4 arcsec
  in the focal plane. Energy resolution provided by
  the CCDs is ?E/E ?10 at 1.5 keV

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Panoram-X Effective Area
Aeff(average)W 600 cm2 (1.2o)2
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The ASTER-X (ASTronomical ExploreR for X-rays)
mission

• Study performed in view of a Probe-Einstein
  class mission (2003 year) under request of
  NASA/GSFC
• Baseline an X-ray telescope able to provide
  1300 cm2 at 1.5 keV and 650 cm2 at 4 keV of
  effective area, with an angular resolution (HEW)
  better than 5 arcsec over a FOV of 30 arcmin
• 2 mirror modules, 12 monolithic shells
• Focal length 7 m
• Max, Min diameters 1020 - 690 mm
• Max, Min height 485 mm, 330 mm
• The focal plane has a curvature radius of 280 mm

• Wall thickness 10 mm constant
• if made in ZerodurTM ? 423 Kg per module
• if made in foamed SiC ? a factor 3 less (at
  least!)

Optical axis
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ASTER-X theoretical performances of the design
HEW of the order of 3 arcsec on most of the FOV,
reaching a value of 5 arcsec at 30 arcmin
off-axis
On-axis effective area 800 cm2 _at_1 keV/
module The reflecting coating is Ir a Carbon
overcoating to enhance the soft X-ray reflectivity
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ASTER-X off-axis vignetting
Aeff(average) x V 400 cm2 x (1.4o)2
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ASTER-X feasibility

• Mirror shells twice longer than WFXT its a
  much more favorable conditions to reduce slope
  errors
• Focal length similar to that used for Chandra
  and XMM
• Mass-to-area ratio just 20 than ROSAT if
  ZerodurTM is assumed

Difference (rms) between Wolter I and polynomial
profiles
Typical rms surface values measured for ROSAT ?
0.5 arcsec Adding 0.5 rms value to our nominal
polynomial profile, we find that the HEW values
increase on average less than 1 and remain
always below 5.
Mirror shell Front surface Rear surface
N 1 2.49 0.46
N 12 2.14 1.28
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Possible implementation of a cluster survey
mission based on the previous concepts
Possible options

• ready-off-the-shelf not (too) expensive mirror
  technology (XMM-like with refined design based on
  Ni) to meet the moderate angular requirement
  (15-25 arcsec HEW).

• use of the same technology and input requirement
  of wide FOV high imaging mission (ASTER-X like
  based on ZERODUR, i.e. glass) to have a 5-10
  arcsec HEW. To have an effective area of 1800 cm2
  this implies a total mirror weight of ? 800 kg x
  Tsurvey/(9 months)

• new technologies under study like slumped glass
  (HEW ? 5-10 arcsec and weight ? 250 T9 kg) or
  already proven SiC (HEW ? 10-20 arcsec and weight
  ? 200 T9 kg)

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Conclusions
Theory strongly constrain Dark Energy equation
and deep survey of the AGN population
Large area cluster survey gt10,000 square
degrees Effective area gt1,800 cm2 and/or survey
time gt 9 months Mean HEW lt 15 arcsec Caveats (to
have 5 arcsec HEW) Ad hoc mirror assembly
(mirrors with different lenghts) Ad hoc focal
plane assembly (inverted pyramid)
Practice feasible from the point of view of
mirrors. Angular resolution depending on mirror
weight
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My personal view

• Microcalorimeters science
• WHIM absorption
• WHIM emission
• GRB
• Superbursts
• Type I X-ray bursts

• CCD science
• Dark energy
• Outskirts of clusters

Science drives
Vision Single telescope (1800 cm2 5-10
HEW) Small FOV microcalorimeter (lt 5x5) CCDs
around (gt 30x30, possibly 40x40) Fast
response and GRB/superburst location capabilities