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Linking Optical and Infrared
Observations with Gravitational
Wave Sources.
Christopher Stubbs
Department of Physics
Department of Astronomy
Harvard University
[email protected]
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Some assertions
•
More celestial events have been seen at optical and IR
wavelengths than have been detected in gravity waves.
•
Next generation surveys will detect essentially all
celestially variable sources, to 22nd magnitude, with
variability that lasts more than a few days, across entire
sky*:
•
•
Supernovae, Quasars/AGN… things that go bump in the night…
•
(*except for ones hiding behind Galactic disk)
Science would benefit from better coordination between
gravity wave and optical variability community.
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Some questions
• What is the relationship between emission of gravity waves,
and optical/infrared (OIR) radiation?
• What OIR variability accompanies GW emission?
Detectable? OIR yes
OIR no
GW no
Sure, look
around…
GW yes
?
-
• How can optical/IR observations be used in conjunction with
GW data (either detections or upper limits) to add to our
understanding?
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Linking OIR and GW data
Gravity wave
view of the sky
Tough, due to OIR
source confusion
We’re pretty
good at this
This link
makes the
most sense
to me
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Optical variability
Optical view
of the sky
Image Subtraction
(High-z Supernova Team)
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Variability is helpful for GW
optical too
• Pointing accuracy for eventual GW
detections is ~ 1 degree
• Optical/IR source density is high
• If we limit attention to variable
sources, candidate list is 2-3 orders
of magnitude smaller.
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Core collapse Supernovae as
an illustrative example
25 solar mass
progenitor
at 10 kpc
SNR~100 at 10 kpc
So LIGO might see
collapse of higher
mass objects out to
1 Mpc (i.e. M31)?
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A New Mechanism for Gravitational Wave Emission in Core-Collapse
Supernovae. Ott, C. et al., PRL 96, 1102 (2006)
A super-dupernova from a 100
solar mass progenitor?
Most luminous SN ever
seen, 75 Mpc away.
Went off during LIGO’s
S5 run!
Optical signature is
huge, what GW signal?
We think we may have
detected another
example at z~0.8 in
ESSENCE survey
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N. Smith et al., astro-ph/0612617
One estimate of optical counterparts to
merging NS-NS binaries
PanSTARRS
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Sylvestre, J, ApJ 591, 1152 (2003)
Optical/IR search options
1. Look at specific galaxies
KAIT survey
2. Look at galaxy clusters
Mt. Stromlo cluster search
Wise observatory search
3. Look at the whole sky*
Killer asteroid surveys: (Spacewatch, NEAT,
LINEAR, LONEOS…)
GRB afterglow surveys: ROTSE, WASP…
Next generation: PanSTARRS, Skymapper, LSST…
All-sky cameras, both optical and IR
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Survey Figure of Merit
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   A
FOM  N / t  

 SNR   sky ()
Source flux,
signal to noise
System:
Collecting Area
Field of View
Efficiency
Site: sky brightness,
seeing
For a given site the system’s effectiveness scales as the A-Omega product, times
the fraction of time allotted to the survey.
Sensitivity to faint sources depends on aperture, not field of view.
Note this simple A-Omega product neglects issues of pixel sampling, site sky
brightness, etc.
Dynamic
range per image is typically ~6 magnitudes. Can extend dynamic range
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to ~10 magnitudes using different exposure times.
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Some OIR Survey Systems
System
Dia (m) FOV (deg) A-Omega
ConCam
0.004
180
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All sky continuous, ~6
WASP
0.1
15
2.2
Triggered, ~17
ROTSE-III
0.45
2
0.8
Triggered, ~18
Raptor
0.07
35
6
Triggered, ~16
ASAS
0.10
3
0.1
All sky, daily, ~14
LINEAR
1.0
1.4
1.9
Ecliptic, ~ 19
SDSS
2.5
1.5
14
Limited survey, ~22
VST
2.6
1
6.8
Allotted time, ~22
PS-1
1.8
2.6
22
“All-sky” Survey, ~22
LSST
8.5
3
650
“All-sky” Survey, ~24
0.1
0.006
Close galaxies, ~19
KAIT SN survey 0.8
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Mode, 60 sec 5 
Tradeoff between revisit cadence and sensitivity
What about the Infrared?
•
Wavelength dependence of extinction favors an IR
variability survey of the Galactic plane.
•
IR does better for attenuation around merging binary
pairs too.
•
Wavelengths beyond 2 microns are really tough from
the ground, due to blackbody emission from the
atmosphere.
•
UKIDSS survey has recent paper on single epoch
Galactic plane survey, but I don’t know of any plans
to do IR all-sky.
•
Absolute magnitude of type II in K band is K ~ -18.
•
A type II behind 100 magnitudes of V band extinction
would be readily detectable with ~1 m class
telescope.
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Existing surveys already enable
“optically triggered” science
Can use optical detections to run constrained “burst”
search in GW data.
Known distances means can set SI unit limits on rate of
change of quadrupole moments.
Great recent example of looking for GW signature from
external trigger is: LIGO team & Hurley, Implications for
the Origin of GRB 070201 from LIGO Observations,
(arXiv:0711.1163)
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SNe that coincided with S5
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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Some are of potential interest…
762 supernovae
during S5
411 core collapse
(spectral confirm.)
89 in named
galaxies
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Went to “virtual observatory”
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Closest Few
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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One potential search scheme
Locations known to subarcsec accuracy, plus redshifts.
This implies arrival time differences at different GW antennas are
known to dt ~ d * L/c ~ (5E-6)*(1000 km)/c ~ tens of nanosec.
Delay between optical peak flux and GW transient is unknown.
So do fixed-delay autocorrelation analysis, sliding over plausible
window in arrival time. This amounts to blending the burst
detection algorithms with known-source analysis.
Could also imagine a stacking scheme, that averages over
multiple optical trigger events (Bence Kocsis).
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Imminent (~12 mo)
• PanSTARRS 1
•
•
•
•
•
1.8 m aperture
7 square degree field
1.4 Gpix imager
Deep depletion detectors
Latitude +20
• Skymapper
• 1.35 m aperture
• 5.7 sq degrees
• Bands optimized for stellar
astronomy
• Latitude 30
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PS 1 on Haleakala
PanSTARRS first
light image of
M31, Andromeda
galaxy.
PS-1 should
detect anything of
interest in M31, in
its microlensing
survey data set,
from 2009-2011.
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PanSTARRS-1: 200 supernovae/month!
1.8m telescope, 7 square degree FOV
Telescope now in shakedown
1.4 Gpix camera, first light in Sept 2007
Image processing pipeline runs end-to-end
Operations likely to begin late 2008
Expect ~ 1 orphan afterglow visible at any time
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In the Planning/Design phase
• Dark Energy Survey
• Equip CTIO 4m with 3 sq deg camera
• 1/3 of the time, 5 year survey
• Cluster photo-z’s, SNe, Weak Lensing, LSS
• PanSTARRS 4
• Four 1.8m telescopes, PS-1 is prototype
• Large Synoptic Survey Telescope
• 8.4m aperture
• 9.6 sq degree field
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Large Synoptic Survey Telescope
Highly ranked in Decadal Survey
Optimized for time domain
scan mode
deep mode
10 square degree field
6.5m effective aperture
24th mag in 20 sec
>20 Tbyte/night
Real-time analysis
Simultaneous multiple science goals
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LSST Merges 3 Enabling Technologies
• Large Aperture Optics
• Computing and Data Storage
• High Efficiency Detectors
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One blind spot = The Milky Way
Spans large solid angle on the sky, Galactic center is at 18
degrees South.
LSST might not even observe at low galactic latitude, due to
high stellar densities (!).
Disk of Galaxy has high extinction in the optical due to “dust”.
This produces the “zone of avoidance” in galaxy catalogs, etc.
But the MW sources we’re seeking (from the GW context) are
going to be really bright transients in the optical/IR.
These considerations motivate an on going modest-aperture
wide angle IR survey that includes the plane of MW.
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Another blind spot: Really bright things!
A type II SN in M31 would peak at about m = 19  24.3 = 5th
magnitude.
This is really bright! LSST will saturate on objects 105 X fainter!
At present we do not have a well-thought-out strategy to hand off
objects across the system of telescopes of different apertures, as
they rise and fall in brightness. There are calibration challenges
due to mis-matched filters and detector efficiencies vs.
wavelength.
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All-sky cameras exist already
ConCam project
R. Nemiroff, MTU
http://nightskylive.net/index.php
Is anyone mining this open-access
data set to search for bright (nearby)
transients?
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Some Opportunities
• Undertake “pointed” GW analysis to look for transient signals
associated with known SNe. Maybe even co-add?
• Ensure optical coverage of all local group galaxies, especially
our own, to detect bright transients. Although rare, let’s not miss
it!
• Undertake frame subtraction processing of ConCam data set,
and other similar all-sky imagers, taking care to not suppress
saturation-level sources.
• Consider in more detail the likely OIR signatures of inspiraling
GW sources, and coordinate with large-aperture surveys
(PanSTARRS, LSST…).
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Some Open Questions
Won’t most detectable GW sources have
accompanying OIR variability? How detectable is this?
Is there merit in establishing coordination and data
reduction pipeline for existing all-sky survey programs?
Drawing a lesson from GRB science, where xray and
optical data did better jointly than separately, how can
we best merge xray, OIR, neutrino and gravity wave
data?
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Summary
Optically triggered GW analysis will deliver real science from
upper limits, and eventually linking detections to optical
counterparts will aid interpretation:
Characterize astrophysics of sources
Independent determination of both redshift and distance
Optical all-sky surveys (down to faint flux levels) will soon be in
operation. We should be able to correlate optical variability with
inspiraling compact object pairs, assuming OIR emission, even
if variability is subtle.
We are less well instrumented/organized for early detection of
bright SNe in the local group of galaxies. SN 1987A in LMC
was found by eye! Two decades later, this would likely again be
the case.
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