Supernova /Acceleration Probe

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Supernova /Acceleration Probe SNAPScience,
Mission, and Simulations

• Alex Kim
• Lawrence Berkeley National Laboratory

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Outline

• Current supernova-cosmology results
• Technique of measuring the Universes dynamics
  and the cosmological parameters with Type Ia
  supernova.
• Current status of supernova and other
  cosmological results and their implications.
• Supernova / Acceleration Probe (SNAP)
• Scientific goals.
• Mission concept.
• SNAP Simulations
• Example studies.
• Justify a space mission.
• Instrument optimization.
• Mission requirements.
• Systematic error control.
• SNAP scientific performance.

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Universe Constituents Dynamics

• Time evolution of the Universes scale depends on
  gravity and constituents.
• Friedmann equations (GR homogenous/isotropic)
• For example if k0 (flat Universe)
• Non-relativistic matter (r a-3 p0)
• Radiation (r a-4 p(1/3)r)
• Cosmological constant (r a0 p-r)
• Dark energy (r a-3(1w) pwr)

Newtons Law of Gravitation
Conservation of Energy
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Universe Constituents Dynamics

• By measuring a(t), we can determine the
  constituents of the Universe, their relative
  amounts, and properties of the dark energy.

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Measuring Universes History and Fatewith
Standard Candles
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Type Ia Supernovae

• Defined empirically as supernovae without
  Hydrogen but with Silicon.
• Progenitor understood as a C/O White Dwarf
  accreting material from a binary companion.
• As the White Dwarf reaches Chandrasekhar mass, a
  thermonuclear runaway is triggered.
• A natural triggered and standard bomb.

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Type Ia Supernovae as Standard Candles

• Peak-magnitude dispersion of 0.25 0.3
  magnitudes
• After correction for light-curve shape,
  supernovae become calibrated candles with 0.15
  magnitude dispersion.
• (define light curve)

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Current SN Results

• Two groups, the Supernova Cosmology Project and
  the Hi-Z Team, find evidence for an accelerating
  Universe.

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Current SN Results
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Current Combined Results
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Implications of an Accelerating Universe

• Models predict a Universe that expands forever.
• The energy density of the Universe is dominated
  by an unexpected form of negative-pressure
  dark energy.
• The Cosmological Constant.
• Why non-zero?
• Why is the dark-energy density so close to the
  matter energy density?
• Some other field, e.g. quintessence.
• Modified gravity.

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Dark Energy and Equation of State

• Parameterized by wp/r.
• Labeled w if constant
• or consider linear expansion ww0wz

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Dark Energy Equation of State
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A Next Generation SN Experiment

• We want to know more
• Confirm that our cosmological models are OK.
• Precision measurements of the cosmological
  parameters.
• Understand the nature of the Dark Energy and the
  implications for fundamental physics.
• A new experiment must
• Provide supernovae at redshifts that provide
  leverage for cosmological parameter and dark
  energy measurements,
• Give a large statistical sample,
• Control sources of systematic error.

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Systematic Errors

• Since the discovery of dark energy, possible
  systematic errors have been identified and
  considered.
• Current supernova results are close to systematic
  error dominated.

Systematic Control
Host-galaxy dust extinction Wavelength-dependent absorption identified with high S/N multi-band photometry.
Supernova evolution Supernova subclassified with high S/N light curves and peak-brightness spectrum.
Flux calibration error Program to construct a set of 1 error flux standard stars.
Malmquist bias Supernova discovered early with high S/N multi-band photometry.
K-correction Construction of a library of supernova spectra.
Gravitational lensing Measure the average flux for a large number of supernovae in each redshift bin.
Non-Type Ia contamination Classification of each event with a peak-brightness spectrum.
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Supernova Sample

• The range and number of supernovae chosen based
  on anticipated residual systematic error.
• A constant number of supernovae with varying
  maximum redshift.
• With the presence of systematic errors, a broad
  redshift range is advantageous.
• For zmax1.7, 2000 supernovae statistical errors
  same order as systematic.

Linder Huterer (2003)
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Mission Design Flowchart
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SNAP Collaboration

• G. Aldering, C. Bebek, J. Bercovitz, M. Bester,
  E. Commins, W. Carithers, C. Day, R. DiGennaro,
  G. Goldhaber, D. Groom, S. Harris, P. Harvey, H.
  Heetderks, S. Holland, D. Huterer, R. W. Kadel,
  A. Karcher, A. Kim, W. Kolbe, J. Lamoureux, R.
  Lafever, M. Lampton, M. Levi, E. Linder, S.
  Loken, R. Miquel, P. Nugent, H. Oluseyi, N.
  Palaio, D. Pankow, S. Perlmutter, K. Robinson, N.
  Roe, M. Sholl, G. Smoot, A. Spadafora, H. von der
  Lippe, J-P. Walder, G. Wang Lawrence Berkeley
  National Laboratory, University of California
  Berkeley, and University of California Space
  Sciences Laboratory
• C. Akerlof, D. Levin, T. McKay, S. McKee, M.
  Schubnell, G. Tarlé, A. Tomasch University of
  Michigan
• R. Ellis, J. Rhodes California Institute of
  Technology
• C. Bower, N. Mostek, J. Musser, S. Mufson
  Indiana University
• A. Fruchter, R. Bohlin Space Telescope Science
  Institute
• G. Bernstein University of Pennsylvania
• S. Deustua American Astronomical Society
• P. Astier, E. Barrelet, A. Bonissent, A. Ealet,
  J-F. Genat, R. Malina, R. Pain, E. Prieto, A.
  Refregier, G. Smadja, D. Vincent France
  IN2P3/INSU/CEA/LAM
• R. Amanullah, L. Bergström, M. Eriksson, A.
  Goobar, E. Mörtsell University of Stockholm
• C. Baltay, W. Emmet, J. Snyder, A. Szymkowiak,
  D. Rabinowitz, N. Morgan Yale University
• (Omnibus paper in preparation, ed. AK)

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A Space Mission

• 3 day synchronous orbit,
• Perigee 2.6 Re (geocentric)
• Apogee 24.9 Re (geocentric)
• This orbit is in the plane of the moon and is
  stable against lunar perturbations. Also,
  simultaneously maximizes solar, lunar, and earth
  avoidance angles.
• Time passage through radiation belts 11.2
  hours
• During this time SNAP is not observing, rather
  performing data dump.
• This corresponds to an 86 operational
  efficiency.
• Total proton dose from belts negligible

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SNAP Telescope

• 2-m primary aperture, 3-mirror anastigmatic
  design.
• Provides a wide-field flat focal plane.

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Instrumentation Imager

• A large solid-angle camera (0.7 square degrees)
  provides multiplexed supernova discovery and
  followup.
• Covers wavelength region of interest, 0.35- 1.7
  microns.
• Fixed filter mosaic on top of the imager sensors.
• 3 NIR bandpasses.
• 6 visible bandpasses.
• Coalesce all sensors at one focal plane.
• 36 2k x 2k HgCdTe NIR sensors covering 0.9-1.7
  µm.
• 36 3.5k x 3.5k CCDs covering 0.35-1.0 µm.

CCDs Guider HgCdTe
Spectrograph
Spectr. port
rin6.0 mrad rout13.0 mrad rin129.120 mm
rout283.564 mm
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Optical Detectors
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Spectrograph

• Integral field unit based on an imager slicer-
  Data cube.
• Input aperture is 3 x 3 reduces pointing
  accuracy req.
• Simultaneous SNe and host galaxy spectra.
• Internal beam split to visible and NIR.

Input port
Prism BK7
Prism CaF2
Slicer
Vis Detector
NIR detector
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Observing Plan

• Repetitive imaging program
• Observe 15 square degrees every four days in all
  filters.
• Provides multiplexed building of supernova light
  curves and discovery on the same images.
• Targeted spectroscopy
• Triggered SN Ia events have individual
  spectroscopic observations near maximum light.

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SNAP Simulations

• Mission performance
• Error budget
• Mission optimization
• Mission comparison
• Simulation Working Group
• R. Amanullah (Stockholm), L. Bergstrom
  (Stockholm), G. Bernstein (Pennsylvania), A.
  Bonissent (CPPM, France), S. Deustua (AAS), M.
  Eriksson (Stockholm), A. Goobar (Stockholm), D.
  Huterer (CWRU), A. Kim (LBNL), J. Lamoureux
  (LBNL), E. Linder (LBNL), S. McKee (Michigan), R.
  Miquel (LBNL), E. Mortsell (Stockholm), N.
  Mostek (Indiana), C. Spitzer (LBNL)

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Supernova Mission Simulator
(AK and simulation group in prep)
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Detection Efficiency

• Determine efficiency of discovering supernova for
  SNAP and ground missions.
• The detection efficiency is determined the
  trigger.
• Minimum 2 points with S/Ngt5 (7) in one (two)
  filters before maximum light.
• SNAP only misses highly-extincted SN at high
  redshift.
• Ground missions lose efficiency for zgt1.1-1.3
  depending on the trigger.
• There is a redshift wall for ground observations
  increase in exposure time gains little redshift
  depth.

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Ground Malmquist Bias

• After stretch correction, Type Ia supernovae have
  an intrinsic magnitude dispersion.
• In a brightness-limited sample, intrinsically
  brighter supernovae are preferentially discovered
  Malmquist bias.
• Malmquist bias produces a bias in the
  determination of dark-energy parameters.
• Fundamental limitation of ground searches.

(AK with E. Linder, R. Miquel, N. Mostek in prep)
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Ground Malmquist Bias

• For a search with maximum redshift z1.3, the
  Malmquist bias error is and statistical error are
  comparable.
• Unless Malmquist bias error is addressed, there
  is no advantage in a search that is statistically
  more aggressive than the z1.3 search.

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Spectrometer Requirements

• Heterogeneity in supernova spectra reflect slight
  differences in supernova explosions and intrinsic
  peak magnitudes.

(G. Bernstein and AK in prep)
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Spectrometer Requirements

• Given a realized supernovas brightness and an
  observing program, the Fisher analysis
  analytically determines the errors in the
  spectral parameters.
• High spectral resolution for feature
  measurements.
• Low spectral resolution to lower instrumental
  noise.
• An optimal spectral resolution is derived to
  minimize error in intrinsic magnitude.

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Calibration Requirements

• We model two approaches to the calibration.
• A single calibration source, e.g. a hot white
  dwarf or a NIST standard, calibrates the entire
  SNAP wavelength range.
• Two independent calibrators calibrate the SNAP
  wavelength range one in the optical and the
  other in the NIR.
• The calibration errors are parameterized by
  temperature errors and correlations of the
  primary standards.

(R. Miquel AK in prep)
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One Calibrator Model

• The cases of a white dwarf is considered.
• T20000K, 1, 10 error

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SNAP Light Curves

• z0.8 z1.0 z1.2
  z1.4 z1.6

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Simulated Hubble Diagrams

• We fit the light curves and spectra a for 1-year
  SNAP mission.

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Cosmological Parameter Determination
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Dark Energy Equation of State
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Cosmological Parameter Determination

• Shown is the w0,w' confidence region of this
  Monte Carlo realization of the SNAP experiment.
  There is a prior on WM and 300 low-z SNe. An
  irreducible systematic is included.

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Conclusion