# Presentation: 501006

## Supernova /Acceleration Probe – SNAPScience, Mission, and Simulations

**Alex Kim**
**Lawrence Berkeley National Laboratory**

## Outline

**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.**

## Universe Constituents & Dynamics

**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”

## Universe Constituents & Dynamics

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

## Measuring Universe’s History and Fatewith Standard Candles

## 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.**

## 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)**

## Current SN Results

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

## Current SN Results

## Current Combined Results

## 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.**

## Dark Energy and Equation of State

**Parameterized by w=p/********.**
**Labeled w if constant**
**or consider linear expansion w=w****0****+w’z**

## Dark Energy Equation of State

## 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. **

## 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. |

## 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)**

## Mission Design Flowchart

## 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)**

## 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

## SNAP Telescope

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

## 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.

- rin=6.0 mrad;  rout=13.0 mrad
- 	rin=129.120 mm;  rout=283.564 mm

- CCDs
- Guider
- HgCdTe

- Spectr. port

- Spectrograph

## Optical Detectors

## 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**

**Slicer**

**Prism**
**BK7**

**Prism**
**CaF****2**

**NIR**
**detector**

**Vis**
**Detector**

## 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.**

## 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)**

## Supernova Mission Simulator

**(AK and simulation group in prep)**

## 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.**

## 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)**

## 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.**

## Spectrometer Requirements

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

**(G. Bernstein and AK in prep)**

## 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.**

## 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)**

## One Calibrator Model

**The cases of a white dwarf is considered. **
**T=20000K, 1, 10% error**

## SNAP Light Curves

**	**** ****z=0.8****	****  z=1.0****	****              z=1.2****	****         z=1.4****	****    z=1.6**

## Simulated Hubble Diagrams

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

## Cosmological Parameter Determination

## Dark Energy Equation of State

## 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.**

## Conclusion