5th Annual Report on GWA-WG2
Joint operation of antennas and network data analysis
M.A. Bizouard2, L. Bosi3, G. Cella5, J. Clark8, A. Corsi, E. Cuoco20, S. D`Antonio4, S.
Fairhurst16, S. Frasca4, G. Frossati 6, G. Guidi7, I.S. Heng8, A. Krolak9,
F. Marion1, B. Mours1, A. Sintes10, A. Ortolan11, A. Pai12, M.A. Papa12, A. Parameswaran12,
I. Pinto13, G.A. Prodi14, T. Regimbau15, E. Robinson18, J. Romano16, F. Salemi17,
B.S. Sathyaprakash16, P. Sutton16, C. van den Broeck16, A. Vecchio18, A.Vicerè7, M. Visco19,
A.deWaard6, G.Woan8
1
CNRS/IN2P3/LAPP, Annecy, France and EGO, Cascina, Italy
2
LAL/IN2P3, Orsay, France
3
INFN and Università di Perugia, Italy
4
INFN Sezione di Roma1, Roma, Italy
5
INFN Sezione di Pisa, Italy
6
University of Leiden, The Netherlands
7
INFN and Universita di Firenze/Urbino, Firenze, Italy
8
University of Glasgow, Great Britain
9
Polish Academy of Sciences, Warsaw, Poland
10
Universitat de les Illes Balears, Palma de Mallorca, Spain
11
INFN Laboratori Nazionali di Legnaro, Italy
12
Max-Planck-Institut für Gravitationsphysik Albert-Einstein-Institut, Golm, Germany
13
INFN and Università del Sannio, Benevento, Italy
14
INFN and University of Trento, Italy
15
CNRS/Observatoire de la Côte d'Azur, Nice, France
16
Cardiff University, Great Britain
17
INFN and University of Ferrara, Italy
18
University of Birmingham, Great Britain
19
CNR/IFSI and INFN Roma, Roma, Italy
20
EGO, Cascina, Italy
Coordinators: G.M. Guidi (INFN, Urbino University), I.S. Heng (Glasgow University)
1.Introduction
The GWA-WG2 focus on promoting information exchange between gravitational
wave data analysts and astronomers has continued into the final year of the project. This year,
in addition to supporting ongoing searches, a search for gravitational waves associated with
glitches in radio frequency pulses from neutron stars was performed. The results of the analysis stressed the importance of using all available information, from simulations and observations, to improve the sensitivity of the gravitational wave search and provide better interpretation of the results.
The ongoing support for joint analysis between the LIGO Scientific Collaboration,
which includes GEO 600, and the Virgo collaboration has helped produced results from the
joint analysis of the S5/VSR1 run. Members from both collaborations came together and
worked hard to learn about the methods and philosophies of their data analysis approaches.
The preliminary results of this work were presented at the GWDAW13 meeting in January,
2009.
To increase interaction between the supernova simulation, neutrino and gravitational
wave communities, a workshop was organized in Cascina which brought together representatives from all three communities. The focus of the workshop was on neutrino transport in
core-collapse supernovae which affects the simulations for gravitational wave emission from
core-collapse supernovae. From the gravitational wave point of view, the discussions from
this workshop provided insight into the physics employed by the simulators. There was also
discussion and exchange of information on the interpretation of results from the different
communities.
2.Status of planned tasks
2.1. Support the joint analysis of data from LSC-Virgo
The joint data analysis by LSC and Virgo collaboration, after the first tests done over
limited periods of time, has started the full analysis of the S5/VSR1 run. This joint run started
on 18th May 2007 and ended on 1st October 2007, summing the second part of the LIGO S5
run and the Virgo VSR1 run.
The joint analysis of S5/VSR1 data for gravitational wave signals from coalescence of
compact binary objects has focused on the so called low mass range. The total binary mass is
then supposed to be between 2 and 35 solar masses. For this mass region, the inspiral part of
the gravitational wave signal is the most important one for the detection by the LIGO and Virgo interferometers. An accurate study of the Virgo noise characteristics has been done in order
to joint analyze the data; these studies have been for example reported in the poster “A PQ
veto for burst and binary inspiral searches using data from Virgo's first scientific run” by MA
Bizouard, and the presentation “Data quality and vetoes for the gravitational wave burst and
inspiral analyses in Virgo's first Science Run” by N Leroy at the Gravitational Wave Data
Analysis Week 13 (GWDAW13 – see http://cgwa.phys.utb.edu/gwdaw13/index.html), January 2009 - these studies serve both to the coalescing binaries and transient un-modeled GW
searches. The analysis has been performed with the standard pipeline used by LSC, which
however had to be adapted to analyze data from 4 interferometers with different characteristics. The work has pushed to revise and propose new methods to be used in the analysis. Several LSC/Virgo presentations have focused on this work; see for example the talk “Status of
the First Search for Gravitational Waves from Compact Binary Coalescences with Joint LIGO-Virgo data” held by J Clayton at GWDAW13. This work is still ongoing. In other searches for GW from compact binary systems, Virgo data have not been used, but the analysis has
gathered researchers from LSC and the Virgo community. In fact, the two collaborations are
now really working together for the analysis of data, both for what regards the actual analysis
as for the development of analysis methods to be used for the next joint data takings.
The search for transient un-modeled gravitational on joint S5/VSR1 data has been
concluded and the collaborations are now working on the final review to be able to publish
soon a paper. The work has been presented by P Shawhan at the GWADW13 (GravitationalWave Burst Searches using LIGO-GEO S5 and Virgo VSR1 data). For the joint all-sky
searches, three pipelines have been used, two previously developed by LSC collaboration and
one by the Virgo collaboration. A new upper limit calculation technique has been developed in
order to be able to combine the results from all pipelines to produce a single upper limit. Other searches for transient signals are on the way, as for example for ring-down signals from oscillating Black holes.
The searches for Continuous waves from pulsars and for the stochastic backgroung of
GW are using at the moment LIGO and Virgo data separately to produce scientific results, but
some method studies are presently under conclusions and will be the base to pursue the analysis using both instruments. However, the analysis of data is done by the two collaborations
jointly.
Finally, a lot of effort has been put in the preparation of the next joint run, which
should start in spring-summer 2009. The work has focused especially on the development of
tools to be able to do real-time searches which will give the possibility to exchange with the
astronomical community possible GW events to be followed by electromagnetic astronomical
observatories – see for example the talk “Real-time searches for un-modeled gravitational
waves burst in the next LIGO-Virgo joint science run” by J Rollins at GWDAW13.
2.2. Support the search for gravitational waves in association with observations in
the electromagnetic spectrum
Radio frequency pulses from pulsars arrive at very regular time intervals. Occasionally, the time between pulses is significantly reduced (often referred to as timing "glitches").
This is thought to be associated with quakes in the neutron star's crust which subsequently
excited the normal modes of the neutron star and cause it to momentarily rotate faster. As neutron star normal modes oscillate, energy is radiated away as gravitational waves.
A joint search for gravitational waves associated with glitches in pulsar timing was
performed by J Clark and IS Heng. A glitch was observed in the Vela pulsar by the Hartebeesthoek radio observatory in South Africa in August 2006. The analysis was performed using data from the two Hanford detectors in the LSC. With some interaction between J Clark
and a contact from Hartebeesthoek radio observatory, S Buchner, the time of the glitch was
refined to within 100 seconds. However, to be conservative, a time window of 1000 seconds
centered on the glitch observation time was set as the on-source period (period when a gravitational wave signal might be observed). The analysis was performed using a Bayesian search
method that was developed and discussed within WG2 and with astrophysicists at previous
WG2 meetings.
While no gravitational waves were observed by the analysis, the importance of incorporating information from theoretical models was stressed. An upper limit on the emission on
gravitational waves from the Vela glitch was set for all possible combinations of signal parameter values. However, if we restrict the signal parameters to values allowed by all known
models for a neutron star's structure (equation of states), the upper limit is 4 times better. It
was also noted that, through closer work with observational and theoretical astronomers, a
better prior on the signal parameters can be determined. The improved prior will increase the
sensitivity of future gravitational wave searches associated with pulsar glitches.
The results of this analysis are currently being written up for submission to a journal.
2.3. Promote the exchange of knowledge between theoretical and DA studies
A workshop on “Supernovae, neutrinos and gravitational waves” was organised on
November 26 in Cascina, Italy – see
http://agenda.infn.it/conferenceTimeTable.py?confId=811 for the link at the scientific program of the workshop.
The workshop focused on the very important subject of generation of GW from Supernovae and the possibility of detection using the Data Analysis methods currently implemented by the GW community or under development. Moreover, a particular attention has
been given to the generation and detection of neutrino signals from these events in connection
with the possibility of performing joint neutrino-GW detection.
The theoretical aspect has been examined in the two opening talks by two experts in
the field whose work makes use of numerical simulations of the astrophysical events to be
able to extract informations about the multiple signals which these events can give (“ The
gravitational wave signal of core collapse supernovae” by E Mueller and “Neutrino signals
from core-collapse events” by T Janka).
Detection of neutrino emitted by supernovae has been the subject of the talk by A Ianni (“SN neutrino detection and perspectives”) who gave a clear view of the present results and
of the working experiments which are in place.
The second part of the workshop focused on the possibility of the joint detection of
GW and neutrino emitted by supernovae (SN neutrinos as an external trigger for GW search”
by G Pagliaroli and a more general talk by S Chatterji who described the GW Data Analysis
methods for transient un-modeled signals like the ones expected from the SN explosions.
Other than from neutrinos from core collapse supernovae, neutrinos of high energy can
be emitted by extragalactic events like binary mergers of compact objects. Currently several
experiments are being developed to be able to detect this type of signals, and the GW community is working to be able to use them for the connected GW signals. On this subject, two
talks, one describing one of these experiments (“The Antares Neutrino telescope: Status Report”, by B Baret), and one on the possibility of joint analysis (“Towards joint searches of GW
and high-energy neutrinos” by E Chassande-Mottin) has been held.
2.4. Preparation of the science case for future detectors
Preparation of the science case for future gravitational-wave detectors is being actively
pursued, with particular emphasis on third-generation ground-based observatories such as the
proposed Einstein gravitational-wave Telescope. The latter will be more sensitive to both
lower (down to a few Hz) and higher (up to 10 kHz) frequencies than existing and planned
observatories such as Advanced LIGO, Virgo, and future upgrades of GEO600.
In the high frequency regime, third-generation detectors are expected to give insight
into neutron star structure. Neutron star quasi-normal modes are assumed to lie in the 1-4 kHz
region, with frequencies and amplitudes that strongly depend on the neutron star equation-ofstate. Neutron stars might also be able to undergo free precession, depending on how strongly
superfluid vortices are ``pinned" to the crust. The gravitational-wave spectrum of fastspinning and precessing neutron stars may provide valuable information on the interaction
between core and crust, and on the properties of the crust itself.
The increased sensitivity at low frequencies will be of interest in the study of the coalescence of stellar mass compact objects such as neutron stars and light black holes, which,
depending on the detector design, may be visible up to redshifts of z ~ 5. This would allow for
a detailed mapping of the mass distribution of such objects over cosmological distances,
which in turn would give us valuable information about stellar evolution in general. It would
also enable us to solve the enigma of gamma ray bursts (GRBs). If short, hard GRBs are associated with compact binary coalescences involving neutron stars, then detailed models could
be tested by constraining the opening angle of the gamma ray ``beam", and by measuring the
promptness of gravitational-wave emission compared with that of the gamma rays. Compact
binary coalescences could also be used as ``standard sirens", analogous to the standard candles of conventional cosmology but in a way that is independent of the cosmic distance ladder.
Finally, very advanced instruments will make it possible to put general relativity to
stringent tests in the strong-field regime. Techniques developed for the space-based LISA to
check for deviations from general relativity in the inspiral process and to constrain parameters
associated with alternative theories of gravity are likely to carry over to third-generation
ground-based detectors. Similarly, it may be possible to test the black hole uniqueness theorem by tracking the motion of stellar mass objects spiraling towards intermediate mass black
holes.
3.Other tasks
IS Heng has performed an investigation into the parameter space covered by gravitational wave signals generated by core-collapse supernova simulations. This work first began
as a result of discussions between IS Heng and H Dimmelmeier at the 2nd ENTApP-GWA
joint meeting in October 2007. Principal Component Analysis was used to create a set of orthogonal basis vectors by decomposing the signal waveform catalogue generated by each series of core-collapse supernova simulations. The study found that the signal waveforms were
very similar and required very few basis vectors to reconstruct the waveforms well. This
meant that the parameter space covered by each simulation is degenerate and one can reduce
the computational cost of any analysis by using the smaller subset of basis vectors instead of
all waveforms in the entire catalogue. This work has been written up as a paper which has
been submitted to the journal Classical and Quantum Gravity.
4. Conclusions
GWA-WG2 has actively worked with its members and the data analysis methods developed from many years of discussion and information exchange are now being applied to
joint search for gravitational waves using LSC and Virgo data. Meetings with theorists and
observational astronomers have enhanced the gravitational wave searches and enriched the
results derived from these searches. There are now much more collaboration between traditional astronomers, observing in the electromagnetic spectrum, and the gravitational wave
community.
As this collaboration progresses, not only will gravitational wave searches be improved but there will also be better interpretation of results from these searches. This will
eventually lead to an era of multi-messenger astronomy, where astrophysical phenomena are
characterised by observations in both the electromagnetic and gravitational wave spectrum.
5. List of publications and conference proceedings
1. I.S. Heng: http://arxiv.org/abs/0810.5707