1. Supernova /Acceleration Probe – SNAP Science, Mission, and Simulations Alex Kim Lawrence Berkeley National Laboratory

2. 2Outline Current supernova-cosmology results —Technique of measuring the Universe’s 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.

3. 3 Universe Constituents & Dynamics Time evolution of the Universe’s scale depends on gravity and constituents. Friedmann equations (GR + homogenous/isotropic): For example if k=0 (flat Universe) —Non-relativistic matter (  ~ a -3 ; p=0) —Radiation (  ~ a -4 ; p=(1/3)  ) —Cosmological constant (  ~ a 0 ; p=-  ) —Dark energy (  ~ a -3(1+w) ; p=w  ) “Newton’s Law of Gravitation” “Conservation of Energy”

4. 4 Universe Constituents & Dynamics By measuring a(t), we can determine the constituents of the Universe, their relative amounts, and properties of the dark energy.

5. 5 Measuring Universe’s History and Fate with Standard Candles

6. 6 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.

7. 7 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)

8. 8 Current SN Results Two groups, the Supernova Cosmology Project and the Hi-Z Team, find evidence for an accelerating Universe.

9. 9 Current SN Results

10. 10 Current Combined Results

11. 11 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.

12. 12 Dark Energy and Equation of State Parameterized by w=p/ . —Labeled w if constant —or consider linear expansion w=w 0 +w’z

13. 13 Dark Energy Equation of State

14. 14 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.

15. 15 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. SystematicControl Host-galaxy dust extinction Wavelength-dependent absorption identified with high S/N multi- band photometry. Supernova evolutionSupernova subclassified with high S/N light curves and peak- brightness spectrum. Flux calibration errorProgram to construct a set of 1% error flux standard stars. Malmquist biasSupernova discovered early with high S/N multi-band photometry. K-correctionConstruction of a library of supernova spectra. Gravitational lensingMeasure 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.

16. 16 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 z max =1.7, ~2000 supernovae statistical errors same order as systematic. Linder & Huterer (2003)

17. 17 Mission Design Flowchart

18. 18 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)

19. 19 A Space Mission 3 day synchronous orbit, Perigee = 2.6 R e (geocentric) Apogee = 24.9 R e (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

20. 20 SNAP Telescope 2-m primary aperture, 3-mirror anastigmatic design. Provides a wide-field flat focal plane.

21. 21 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. r in =6.0 mrad; r out =13.0 mrad r in =129.120 mm; r out =283.564 mm CCDs Guider HgCdTe Spectr. port Spectrograph

22. 22 Optical Detectors

23. 23Spectrograph 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 Slicer Prism BK7 Prism CaF 2 NIR detector Vis Detector

24. 24 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.

25. 25 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)

26. 26 Supernova Mission Simulator (AK and simulation group in prep)

27. 27 Detection Efficiency Determine efficiency of discovering supernova for SNAP and ground missions. The detection efficiency is determined the trigger. Minimum 2 points with S/N>5 (7) in one (two) filters before maximum light. SNAP only misses highly- extincted SN at high redshift. Ground missions lose efficiency for z>1.1-1.3 depending on the trigger. There is a redshift wall for ground observations – increase in exposure time gains little redshift depth.

28. 28 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)

29. 29 Ground Malmquist Bias For a search with maximum redshift z=1.3, 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 z=1.3 search.

30. 30 Spectrometer Requirements Heterogeneity in supernova spectra reflect slight differences in supernova explosions and intrinsic peak magnitudes. (G. Bernstein and AK in prep)

31. 31 Spectrometer Requirements Given a realized supernova’s 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.

32. 32 Calibration Requirements We model two approaches to the calibration. a.A single calibration source, e.g. a hot white dwarf or a NIST standard, calibrates the entire SNAP wavelength range. b.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)

33. 33 One Calibrator Model The cases of a white dwarf is considered. —T=20000K, 1, 10% error

34. 34 SNAP Light Curves z=0.8 z=1.0 z=1.2 z=1.4 z=1.6

35. 35 Simulated Hubble Diagrams We fit the light curves and spectra a for 1-year SNAP mission.

36. 36 Cosmological Parameter Determination

37. 37 Dark Energy Equation of State

38. 38 Cosmological Parameter Determination Shown is the w 0,w' confidence region of this Monte Carlo realization of the SNAP experiment. There is a prior on  M and 300 low-z SNe. An irreducible systematic is included.

39. 39Conclusion