USING TRANSIENTS TO
ILLUMINATE
THE DARK UNIVERSE
R. Chris Smith
NOAO/CTIO
ESSENCE, SuperMACHO, and
the Dark Energy Survey
Today’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 illuminate
the 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 Primer
star
mass M
detector
Macho collaboration
• Gravitational amplification of the light of an
unresolved light source
• Depends on mass, velocity, and
geometry(b, D1, D2). Degeneracy!
MACHO
Project
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
Where
are the
lenses?
We need many more LMC microlensing events
SuperMacho
• Study microlensing towards the LMC
SuperMacho
• 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
• s = 0.1 mag at 23rd
• http://www.ctio.noao.edu/~supermacho
Microlensing event
candidates in 2003
• About 50 microlensing candidates (X2<4.0)
• 25 spectra in 2003
peak @ 22 mag, u_min < 0.53
peak @ 18.9 mag, u_min =1.5 (low-amp event)
Main contaminant:
SNe behind the LMC
• 70 candidates in 2003 alone!
SN Ia @ z=0.25, peak mag 20.8
peak mag 23.1
Brief History of Dark Energy
• 1990s
 Wanted to measure the DECELERATION of
the Universe
 Use SUPERNOVAE as cosmic yardsticks
Type Ia SNe
One Parameter Family
Standardizable
Candles
• Color
• Rate of decline
• Peak brightness
-- gives -δd/d ~ 0.06
s ~ 0.13 mag
(Supernova Cosmology Project, Kim et al)
An Accelerating Universe?!
Riess et. al. 1998
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 energy
 Key parameter, “w”, in generalized EOS P=wρ
 w = -1 for cosmological constant
Attacking 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 Energy
ROADMAP 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!
ESSENCE
• GOAL: Constrain value of w to within about 10%
• Need ~200 Type Ia SNe: Populate bins of Dz=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 + 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 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 followup 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
•
•
•
•
•
Repeatable
Reliable
Wide-field
Multi-color
Imaging
• CTIO Blanco 4m + MOSAIC II
• Every other night, Oct - Dec, 2002-2006
The 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+SuperMACHO
The 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 Layout
… 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 nearreal time, classify ASAP
• Remove instrumental artifacts
Flatfield, illumination, astrometric & photometric calib
• Frame subtraction to identify transients
Geometrical registration
Convolution with varying kernel
Subtraction
Object identification on difference image
• Classification (SN, asteroid, etc.)
Need a LOT of information to do well
Usually requires several visits
Searching for SNe, MLs,
and other transients
High-z SN Team
Web based management
• “Web-sniff” preliminary pass
Eliminate most false positives
• Good candidates moved to “Alert list”
Reviewed again, ranked priority
• Put on spectroscopic target list
Ranked by spec priority
• Updated as spectroscopy comes in
• See web pages…
Public 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 2003
Discovery rates –
-1
40 yr goal
Year
Ia
II/Ib/I
c
??
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 Cosmology
Jose Luis Prieto
Data Management:
Distribution
• No proprietary period on survey images
Distribute RAW data ASAP after observations
Distribute REDUCED (flat-fielded) data soon
after (final?) reduction
• No proprietary period on transient
announcements and followup information
SN and other transients posted to web in real
time, also announced via IAUCs and email
Additional spectroscopic info also posted
Future: 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 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 survey
• Dark Energy Survey team to dedicate ~10% of
time for SN search and science
• Strawman strategy
 1 hour per night for 4 months for 5 years
 riz in ~40 sq-deg
 3 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 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
s 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.