USING TRANSIENTS TOILLUMINATETHE DARK UNIVERSE

USING TRANSIENTS TOILLUMINATETHE DARK UNIVERSE

R. Chris SmithNOAO/CTIO

ESSENCE, SuperMACHO, andthe Dark Energy Survey

Today’s BIG Questions:Dark Energy & Dark MatterToday’s BIG Questions:Dark Energy & Dark Matter

Dark Energy is the dominant constituent of the Universe.Dark Matter is next.

95% of the Universe is in Dark Energy and Dark Matter, for which we have little or no detailed understanding.

1998 and 2003 Science breakthroughs of the year

Transients illuminatethe Darkness Transients illuminatethe Darkness • Dark Matter

Microlensing a key probe of local dark matter

Previous microlensing surveys provided enigmatic results; more questions to be answered

• Dark Energy Supernovae are the most precise distance indicators at large distances

First clear indications of dark energy came from studies of distant supernova light curves

Microlensing PrimerMicrolensing Primerstar

D2

D1

detectorb

mass M

Macho collaboration

• Gravitational amplification of the light of an unresolved light source

• Depends on mass, velocity, and geometry(b, D1, D2). Degeneracy!

Assumes uniform priors in f and log(m)

Best fit is f = 0.2, M=0.5

Note that f = 0 and 100% are both excluded!

Even at f=0.2, this is more mass than all known MW components

Assumes uniform priors in f and log(m)

Best fit is f = 0.2, M=0.5

Note that f = 0 and 100% are both excluded!

Even at f=0.2, this is more mass than all known MW components

MACHO ProjectMACHO Project

WhereWhere are the are the lenses?lenses?

We need many more LMC microlensing events

SuperMachoSuperMacho

• Study microlensing towards the LMC

SuperMachoSuperMacho

• Goal: Differentiate between whether lenses are in the LMC or Halo

• Need ~50 well-characterized events• Single band: “VR” = 5200–7200Å• ~60 fields = ~21 deg2

• Half-nights every 2 nights for 3 months (Oct-Dec)

• Exposure times optimized to maximize # of stars, ranging from 20s to 200s

• = 0.1 mag at 23rd• http://www.ctio.noao.edu/~supermacho

peak @ 22 mag, u_min < 0.53 peak @ 18.9 mag, u_min =1.5 (low-amp event)

• About 50 microlensing candidates (X2<4.0)

• 25 spectra in 2003

Microlensing event candidates in 2003Microlensing event candidates in 2003

SN Ia @ z=0.25, peak mag 20.8 peak mag 23.1

• 70 candidates in 2003 alone!

Main contaminant:SNe behind the LMCMain contaminant:SNe behind the LMC

Brief History of Dark EnergyBrief History of Dark Energy

• 1990s

Wanted to measure the DECELERATION of the Universe

Use SUPERNOVAE as cosmic yardsticks

One Parameter FamilyOne Parameter Family

StandardizableStandardizableCandlesCandles

(Supernova Cosmology Project, Kim et al)

~ 0.13 mag

• Color

• Rate of decline

• Peak brightness

-- gives --

δd/d ~ 0.06

Type Ia SNeType Ia SNe

An Accelerating Universe?!An Accelerating Universe?!

Riess et. al. 1998

A Repulsive Result!A Repulsive Result!

• Expansion of Universe is accelerating!!!• Implies NEW PHYSICS!• Regions of empty space REPEL each other!

“Cosmological constant”? • Einstein’s greatest blunder… OR NOT?!!

Something going on in the vacuum?

• Characterize equation of state of dark energyKey parameter, “w”, in generalized EOS P=wρw = -1 for cosmological constant

Attacking the Questions of Dark Matter & Dark EnergyAttacking the Questions of Dark Matter & Dark Energy• “Classical” approach won’t work

Not enough telescope time Difficult to control calibrations & systematics

• LARGE SURVEYS Goal: Provide large, uniform, well calibrated, controlled, and documented datasets to allow for advanced statistical analyses

Control calibrations & systematics to <1% Larger collaborations provide both manpower and diverse expertise• Including both traditional astronomers and high-energy physicists

Dark EnergyROADMAP to understandingDark EnergyROADMAP to understanding• Today

ESSENCE, rolling search 3 months per year CFHT SNLS, more time = more Supernovae!

• Coming Soon to a telescope nearby PanSTARRs

• PanSTARRs 1 going into operations in 2006• PanSTARRs 4 moving forward

Dark Energy Survey• Camera to be built by Fermilab w/ DOE funding (2009?)

• The next BIG step LSST

• Scanning the sky repeatedly to around 24th mag

• Stepping UP Space-based work: JDEM (SNAP and/or others)

• Going after higher redshift, and higher order effects!

ESSENCEESSENCE

• GOAL: Constrain value of w to within about 10%

• Need ~200 Type Ia SNe: Populate bins of z=0.1 in range of 0.15 < z < 0.75

• Multiple bands: RI, R=200s to get out to z~0.8 Cover redshift range and SN colors

• ~32 fields = ~12 deg2

• 16 fields in half nights every 4 nights for 3 months

• http://www.ctio.noao.edu/wproject or http://www.ctio.noao.edu/essence

Today:ESSENCE + SuperMACHOToday:ESSENCE + SuperMACHO• Use a LARGE (~200 SNe), UNIFORM set of supernova light curves to allow us to study the evolution of the expansion of the universe Constrain “w”, the equation of state parameter of Dark Energy, to ~10%

• Use other half of nights to constrain possible DARK MATTER candidates The ‘SuperMACHO’ project Search the Large Magellanic Cloud for microlensing

• 30 SN+SM nights/year for 5 years (2002-2006)

Common RequirementsCommon Requirements

• Detect and follow faint transients with variability on timescales of days Detection of faint transients on complicated backgrounds

Area+Depth: Need wide field + ~4m aperture Sampling: between nightly and weekly

• Rapid transient detection for alerts and planning of follow-up observations Ability to process >20 GB/night in near real time

Detections matched against catalogs: new object?

Transient alerts <12 hours after observations for follow-up on large telescopes

The Strategy The Strategy

• Repeatable• Reliable• Wide-field• Multi-color• Imaging

• CTIO Blanco 4m + MOSAIC II• Every other night, Oct - Dec, 2002-2006

The Strategy: DetailsThe Strategy: Details

• “Rolling” Searches Continuous (3 month) search:

• Half night every other night (dark+grey) for 3 mo.• Actually visit SAME field every 4th night; adequate light curve coverage for intermediate z SNe

Multi-color search in RI (SNe) and VR (MLs)• Multi-color light curves for “free”• No CR splits

require coincidence in 2 bands AND/OR across >2 epochs SNe Equatorial fields (+5 to -30), SM in LMC

• Including fields in NDWFS Cetus, SDSS overlap, etc. Monitor 12 sq. deg. (ESSENCE), 25 sq. deg (SM) Exposure times optimized for distribution of SN z

• ESSENCE: Expect ~20 SNe / month (all types)• SuperMACHO: Expect ~3-4 microlensing events / month

ESSENCE+SuperMACHOThe data flows…ESSENCE+SuperMACHOThe data flows…• The telescope

CTIO’s Blanco 4m

• The camera MOSAIC 8Kx8K imager (67 megapixels)

• Exposures of 60s to 400s• Collect 20GB of RAW data per night• Data must be reduced and analyzed in near REAL TIME (within ~30min)

• Data ‘Reduction’ = 5x EXPANSION! Roughly 3TB per year

Hardware LayoutHardware Layout

… and flows… and flows

• much larger data flow than most other astronomical projects

• With ADDITIONAL complication of real-time reduction & alert requirement Must plan spectroscopic follow up on largest telescopes (Gemini, Keck, VLT, Magellan, …)

• We THOUGHT we were ready A few CPUs (cluster of 20 x 1GHz)A few disks (4 x 4TB “data bricks”)

• But…

Identify variability in near-real time, classify ASAPIdentify variability in near-real time, classify ASAP

• Remove instrumental artifacts Flatfield, illumination, astrometric & photometric calib

• Frame subtraction to identify transientsGeometrical registrationConvolution with varying kernelSubtractionObject identification on difference image

• Classification (SN, asteroid, etc.)Need a LOT of information to do wellUsually requires several visits

Searching for SNe, MLs, and other transientsSearching for SNe, MLs, and other transients

High-z SN Team

Web based managementWeb based management

• “Web-sniff” preliminary passEliminate most false positives

• Good candidates moved to “Alert list”Reviewed again, ranked priority

• Put on spectroscopic target listRanked by spec priority

• Updated as spectroscopy comes in

• See web pages…

Public Web AnnouncementsPublic Web Announcements

• Announcements immediately upon confirmation

• RA, Dec, magnitudes, offsets• Finder charts: PDF, PS, and FITS data!• redshift (to one decimal) when known• all SNe sent to IAU Circulars• SNe used by two projects for I-band cosmology at z=0.5 (CSP and PUC)

• Final reductions archived in NOAO Science Archive

IAU Circulars – Oct 2003IAU Circulars – Oct 2003

Discovery rates – 40 yr-1 goalDiscovery rates – 40 yr-1 goal

Year Ia II/Ib/Ic

??

2002/3 15 2 2

2003/4 37 3 14

2004/5 40 6 13

Total 92 11 32

SN Ia @ z=0.68

Initial CosmologyInitial Cosmology

Jose Luis Prieto

Data Management: DistributionData Management: Distribution• No proprietary period on survey images

Distribute RAW data ASAP after observationsDistribute REDUCED (flat-fielded) data soon after (final?) reduction

• No proprietary period on transient announcements and followup informationSN and other transients posted to web in real time, also announced via IAUCs and email

Additional spectroscopic info also posted

Future: Dark Energy CameraFuture: Dark Energy Camera

• Proposal by Fermilab, CTIO, Univ. Chicago, Univ. Illinois, NCSA, LBNL, and more each month!

• Dark Energy CAMERA 2-deg diameter imager, pi square degrees on CTIO4m

• Dark Energy SURVEY FOUR complementary science projects

• Cluster work (based on SZ work), Weak Lensing, SNe

5000 sq. deg covered in griz (cluster and lensing)

30% of time on CTIO 4m over 5 years, 2009–2014

The Data:Dark Energy SurveyThe Data:Dark Energy Survey• Each image ~ 1GB• 350 GB of raw data / night• Data must be moved to NCSA before next night begins (<24 hours) >36Mbps internationally

• Data must be processed within ~24 hours Need to inform next night’s observing

• Total raw data ~0.2 PB• TOTAL Dataset 1 to 5 PB

Reprocessing planned using Grid resources

Dark Energy Camera SN surveyDark Energy Camera SN survey

• Dark Energy Survey team to dedicate ~10% of time for SN search and science

• Strawman strategy1 hour per night for 4 months for 5 yearsriz in ~40 sq-deg3 day sampling for each field

• >2000 SNe in range 0.25 < z < 0.75• statistical accuracy of 0.02 in w

NOT including systematics!Floor probably well above

Dark Energy Camera SNeDark Energy Camera SNe

Projected constraints on WM and w from the five-year DES SN survey. A flat cosmology has been assumed. Red: the SN survey alone; blue: joint constraints from SNe + 2dF (WM = 0.278 ± 0.042) (left) and joint constraints from SNe and the SPT +DES cluster survey (right). Contours represent 1, 2, and 3 confidence levels. The curves at right represent the constraints on w after marginalization over WM.

BUT CAN WE DO THIS WITH LIMITED SPECTROSCOPY?

Simulations by G. Miknaitis, using Tonry-tool

• Hi-ho, hi-ho…Back to looking for diamonds in the data mines.