Download LIGO Listens for Gravitational Waves

Following Up Gravitational Wave
Event Candidates
Roy Williams (Caltech),
Peter Shawhan (U Maryland),
for the LIGO Scientific Collaboration
and Virgo Collaboration
LSST All Hands Meeting 2012 August 14
LIGO-G1200782
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Sources of Gravitational Waves
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Compact binary coalescence
Stellar core collapse
Bill Saxton,
NRAO/AUI/NSF
e.g. neutron stars or black holes
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Neutron stars
Periodic from bump
Non-periodic from flare
Casey Reed/PSU
h(t)
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Cosmic strings
)
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► Early Universe
Like CMB
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and others…
The challenge: Expected strain amplitudes at Earth are 10–21 or less
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A Full-Size GW Detector
LIGO Hanford Observatory (Washington state, USA)
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Advanced LIGO will be a Vast Improvement
Image courtesy Beverly Berger and atlasoftheuniverse.com
Best estimate: will
detect dozens of
mergers per year*
*”Rates paper” 1003.2480
Factor of ~10 better amplitude sensitivity than initial detectors
 Factor of ~1000 greater volume of space
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Advanced Detector Network, ~2015 and Later
GEO-HF
KAGRA
Advanced LIGO
600 m
4 km
4 km
3 km
3 km
4 km
Advanced
LIGO
LIGO-India
Advanced VIRGO
(proposed)
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Global GW Observatory
Data courtesy LIGO/LSC http://www.ligo.org/science/GW100916/
Sky localization by
time differences
Need at least 3 operating
detectors to localize signals
Coordinate science runs and downtimes
when possible
ROUGH GUIDE to typical error region areas:
2 detectors: ~1000 square degrees (annulus)
3 detectors: tens/hundreds square degrees
4 detectors: ~10 square degrees
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Impact of Follow-up Observations
Finding an optical/radio/X-ray/neutrino transient will put the GW
event candidate in an astronomical context
Much more science!
May be able to confidently detect a somewhat weaker GW event (spectral)
Localize in a host galaxy (or outside!)
Compare GW and electromagnetic emissions: strength, time, etc.
Allow better parameter estimation from the GW data
Need to manage probability of false (unrelated) associations
Classification of transients will be essential
Should have a handle on the normal population of similar transients
In 2009–2010:
Program active for 10 weeks of LIGO-Virgo joint observing
Nine event candidates were followed up by at least one telescope
Including two by Swift (XRT & UVOT)
[ Evans et al., arXiv:1205.1124 ]
No stand-out candidates, unfortunately
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Supernova vs Binary Inspiral
CC Supernova is a detonation
 BRIGHT
Can be seen to edge of Universe
Binary Coalescence is an impact
 Fainter
But bright along jet axis (= short GRB)
Metzger and Berger
1108.6056
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upper limit
Post merger accretion
Van Eerten/MacFadyan
1102.4571
Figs: Metzger and Berger
observation
On Axis
LSST is Essential
The range of
existing SGRB
optical afterglows …
indicates that
observations with
LSST are essential.
Off Axis
Isotropic kilonova
Metzger and Berger
1108.6056
-- Metzger and Berger
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LIGO Hanford
GEO 600
Virgo
LIGO Livingston
Transfer data
Swift: NASA E/PO, Sonoma State U., Aurore Simonnet
Rapid Alerts for Follow-up Observations
KAGRA
LIGO-India
Send info
to observers
GW
data
Analyze data,
identify triggers,
infer sky position
Estimate background
Validate
Trigger
database
Select event
candidates
Goal: Catch a counterpart that would have been missed
(or detected only later)
Missed GRB, orphan afterglow from off-axis or “failed” GRB, kilonova, …
 Localize accurately, compare GW & EM emissions
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Communication with Follow-up Observers
Assemble event candidate information
Type of signal, significance, time, sky map, estimated physical params (?)
Format as a VOEvent, for instance
Send alert to observers
Plan to use standard channel(s) like GCN/TAN, VOEventNet
May have revised / refined information to distribute later
LSC and Virgo committed to releasing public alerts in the long run
Early on, work with partners through MOUs until a few GWs are detected
Policy: http://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=89391
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Observing Partners During 2009–2010
XRT
UVOT
1.2 m
2m
LSST, 6.7m
1.3 m
1m
1m
APERTURE
Mostly (but not all) robotic wide-field optical telescopes
Many of them used for following up GRBs, surveying for supernovae and
other optical transients
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Observing Partners During 2009–2010
25 sq deg
20×20°
3.4
7.3 sq deg
sq deg
3.4
3.4
sq deg
sq deg
XRT
UVOT
LSST
9.4 sq deg
3.4
sq deg
3.4
sq deg
FIELD OF VIEW
5.7
sq deg
3.4
sq deg
Mostly (but not all) robotic wide-field optical telescopes
Many of them used for following up GRBs, surveying for supernovae and
other optical transients
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Event of 20100916 the “Big Dog”
Coherent WaveBurst probability sky map:
The
“Big Dog”
Top 1000 pixels reported
• total area: 160
129 sq deg
• est. containment: ~19%
Phase rings
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Galaxy Prior
Probably (maybe not*) GW
sources stay near their
places of birth …
Use positions of
known galaxies within
50 Mpc
White et al., CQG 28,
085016
Star formation proxy = blue
light luminosity
Galaxies not so useful at 200
Mpc – too many.
False positives are
concentrated on the galaxies
* Fong et al 1012.4009
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Follow-up for Big Dog
nearby
galaxies
SkyMapper
TAROT,
ROTSE
Images taken within 44
min after event, 2 min
after LIGO event, and on
subsequent nights
… turned out to be blind injection 
Zadko
Swift
Zadko
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Summary
Gravitational wave detectors are operated as a global network
Data combined and analyzed coherently
Advanced LIGO and Virgo upgrades are in progress
First science runs planned for 2015–16
Might be years to full sensitiviy and good localization
KAGRA and LIGO-India to join too
Have begun a program of producing and sending rapid alerts
Supports both prompt and delayed follow-up observations
Many lessons learned from the 2009–10 science run
Now preparing an improved future program with easy MOU
Transition to public alerts planned after detection of 4 GW events