Date post: | 15-Dec-2015 |
Category: |
Documents |
Upload: | melanie-shrewsberry |
View: | 215 times |
Download: | 1 times |
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
))) Sources of Gravitational Waves
► Compact binary coalescence ► Stellar core collapsee.g. neutron stars or black holes
► Neutron stars ► Cosmic stringsPeriodic from bumpNon-periodic from flare
► Early UniverseLike CMB
The challenge: Expected strain amplitudes at Earth are 10–21 or less
2
h(t)
Bill
Sax
ton,
N
RA
O/A
UI/
NS
F
Cas
ey R
eed/
PS
U
)))
► and others…
4
))) Advanced LIGO will be a Vast Improvement
4
Factor of ~10 better amplitude sensitivity than initial detectors Factor of ~1000 greater volume of space
Best estimate: will detect dozens of
mergers per year*
*”Rates paper” 1003.2480
Imag
e co
urte
sy B
ever
ly B
erge
r an
d at
laso
fthe
univ
erse
.com
)))
5
Advanced Detector Network, ~2015 and Later
GEO-HF
Advanced VIRGOAdvanced LIGO
Advanced LIGO
4 km4 km
4 km
600 m
3 km 3 km
LIGO-India (proposed)
KAGRA
))) Global GW Observatory
Sky localization by time differences
Da
ta cou
rtesy LIG
O/LS
C h
ttp://w
ww
.ligo.org
/science
/GW
100
916/
ROUGH GUIDE to typical error region areas:2 detectors: ~1000 square degrees (annulus)
3 detectors: tens/hundreds square degrees
4 detectors: ~10 square degrees
Need at least 3 operating detectors to localize signals
Coordinate science runs and downtimes when possible
7
))) 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) associationsClassification 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)
No stand-out candidates, unfortunately
[ Evans et al., arXiv:1205.1124 ]
Mult
i-mes
seng
er
astro
nom
y
7
8
))) Supernova vs Binary Inspiral
Binary Coalescence is an impact
Fainter
But bright along jet axis (= short GRB)
CC Supernova is a detonation
BRIGHT
Can be seen to edge of Universe
Metzger and Berger1108.6056
9
))) LSST is Essential
The range of existing SGRB optical afterglows … indicates that observations with LSST are essential.-- Metzger and Berger
On
Axi
sO
ff A
xis
observation
upper limit
Post merger accretionVan Eerten/MacFadyan1102.4571
Isotropic kilonovaMetzger and Berger1108.6056
Fig
s: M
etzg
er a
nd B
erge
r
10
))) Rapid Alerts for Follow-up Observations
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
LIGO Hanford
LIGO Livingston
GEO 600
Virgo
LIGO-India
KAGRA
GW data
Analyze data, identify triggers,infer sky position
Estimate background
Trigger database
Select event candidates
Validate
Transfer data
Send infoto observers
Sw
ift:
NA
SA
E/P
O,
So
no
ma
Sta
te U
., A
uro
re S
imo
nn
et
))) Communication with Follow-up Observers
Assemble event candidate informationType of signal, significance, time, sky map, estimated physical params (?)
Format as a VOEvent, for instance
Send alert to observersPlan 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 runEarly on, work with partners through MOUs until a few GWs are detectedPolicy: http://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=89391
11
12
))) Observing Partners During 2009–2010
XRTUVOT
APERTURE
2 m
1 m
1.2 m
1.3 m
1 m
Mostly (but not all) robotic wide-field optical telescopesMany of them used for following up GRBs, surveying for supernovae and other optical transients
LSST, 6.7m
13
))) Observing Partners During 2009–2010
FIELD OF VIEW
XRTUVOT
20×20°
7.3 sq deg
9.4 sq deg
25 sq deg
3.4 sq deg 3.4
sq deg
5.7 sq deg
3.4 sq deg
3.4 sq deg
3.4 sq deg
3.4 sq deg
Mostly (but not all) robotic wide-field optical telescopesMany of them used for following up GRBs, surveying for supernovae and other optical transients
LSST
))) Event of 20100916 the “Big Dog”
Top 1000 pixels reported• total area: 129 sq deg• est. containment: ~19%
14
Coherent WaveBurst probability sky map:
The “Big Dog”
Phase rings
160
15
))) 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
))) Follow-up for Big Dog
nearby galaxies
TAROT,ROTSE
SwiftSkyMapper
Zadko
Zadko
16
Images taken within 44 min after event, 2 min after LIGO event, and on subsequent nights
… turned out to be blind injection
Summary
Gravitational wave detectors are operated as a global networkData combined and analyzed coherently
Advanced LIGO and Virgo upgrades are in progressFirst 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 alertsSupports 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