1. Upper limits on gravitational wave bursts
radiated from stellar-core collapses in our Galaxy
Masaki Ando (Department of Physics, University of Tokyo)
Tomomi Akutsu, Tomotada Akutsu, Koji Arai, Youichi Aso, Mitsuhiro Fukushima, Kazuhiro Hayama, Nobuyuki Kanda, Kazuhiro Kondo, Norikatsu Mio, Shinji Miyoki, Shigenori Moriwaki, Shigeo Nagano, Shuich Sato, Masaru Shibata, Hideyuki Tagoshi, Hirotaka Takahashi, Ryutaro Takahashi, Daisuke Tatsumi, Yoshiki Tsunesada, Toshitaka Yamazaki,
and the TAMA collaboration
Overview
Predicted waveforms of stellar-core collapse　　　
TAMA300 data : Data Taking 9
Data analysis　 : Excess power filter
Fake reduction
Galactic simulation : Signal injection simulation
Upper limit for Galactic events
(90% C.L.)
Galactic event rate :
5 x 103 events/sec
4 x 10–4 Moc 2/sec
GW energy rate :
Target waveform
Observation with the TAMA300 detector
Targets: Burst gravitational waves
from stellar-core collapses
TAMA300, an interferometric GW detector in Japan
Baseline length : 300m
Fabry-Perot-Michelson inter-
ferometer with power recycling
Placed at National Astronomical
Observatory in Japan
Relativistic, axisymmetric numerical simulation
by Dimmelmeier et al.
DT6
Noise floor level drift
DT8
26 waveforms
Amplitude h rss : 4 x /Hz1/2 (at 8.5kpc)
Energy E tot : 9 x 10-8 Moc2
9 observation runs,
Total data : ~3000 hours
DT9
H.Dimmelmeier et al,
Astron. Astrophys. 393 (2002) 523.
Data Taking 9
Nov. 28, – Jan. 10, 2004
558 hours of data
　　Noise level : 2x10-21 /Hz1/2
This analysis …
2nd half : 200 hours
(Christmas, new-year holidays)
Better noise level
Stable environment
Short burst waves Spike wave ~1msec
Duration time <30msec
(optimal direction, polarization)
Data-analysis methods
Galactic simulation
Burst filter: Excess-power filter
Evaluate signal power in given time-freqency regions
Monte-Carlo simulation
　　Random events
　　Inject signal to real data
　　Analyze data with same codes
Investigate
‘what happens with real signals’
 compare with obs. results
Time- Frequency plane
(spectrogram)
Raw Data (time series)
Fourier
transform
Position : Somewhere in Galaxy
Exponential Disk model
Freq. sum
Galactic-event
distribution
R = (x 2+y 2) ½, Rd : 3.5 kpc, hd : 325 pc
Few assumptions for signal …
time-frequency bands
Robust for waveform uncertainties
Total power
in given T-F region
Time ： Somewhere in DT9 (200hr)
Detector angular depend.
Source :
26 Dimmelmeier waveforms
Random angle
Source angular depend.
Signal !!
Selected parameter:
Dt = 12.8 [msec]
Df = 2300 [Hz]
Effective distance
Data conditioning
Upper-limit results
Line removal
AC line, Violin mode line,
Calibration line
Without Line Removal
Event candidates
Event-selection threshold : SNR>2.9
Method
FFT 72sec data
Reject line freq. components
Inverse FFT
Detection efficiency : 1x10-5
Observation result : 7x10-2 events/sec
Upper limit
With Line Removal
Assume a Poisson distribution
for the observed event number
N obs  N ul
Normalization (whitening)
　　 Normalize each spectrum
by 30-min. averaged noise spectrum
Veto of fake events
Time-scale selection
Galactic event rate
Burst signal < 100 msec
Most detector noises > a few seconds
Effective to long-duration noises
5 x 103 events/sec
GW energy rate
4 x 10–4 Moc 2/sec
Veto with monitor channels
(90% C.L.)
Correlated bursts in
intensity monitor channel
Effective to short spikes
False-dismissal rate: less than 2%
(estimated by signal-injection tests)
Reference: M.Ando et al., Phys. Rev. D 71, (2005)