K.Somiya Detection of blackhole ringdown signals using quasi normal mode harmonics (Status talk of A04:15H00778) 5th annual symposium of the innovative area Dec. 2016 Tokyo Institute of Technology K.Somiya and S.Atsuta K.Somiya

BH inspiral and ringdown In GW150914 the inspiral signal is clear while the ringdown is not so clear (ringdown freq ~ 250Hz). -> Is it possible to increase the SNR for the ringdown? -> Is it possible to detect BH only from its ringdown signal?

aLIGO current sensitivity and KAGRA's goal sensitivity We recently changed a design of the suspension and the thermal noise peak moved away from the ringdown frequency of 60Ms BH. A 60Ms ringdown is quite suitable for the current aLIGO sensitivity.

Can we detect a QNM alone? gravitational wave time It is not easy to distinguish a signal from nonstationary noise as decaying sine waves are too common in the nature. Using not only the 22 mode but also its harmonics, we may be able to increase the SNR for the ringdown.

Ringdown signal decay rate and amplitude (Average spin before collision) Leaver 1985 Kamarestos 2012 QNM frequencies was derived long time ago. QNM amplitudes can be estimated now with NR.

What is the best way to use HOMs? (a) coincidence search (b) MF with HOMs Data Data Matched filter with a wave with 22+33 modes Matched filter with a 22 mode Matched filter with a 33 mode Compare the arrival time (a) would be no good as SNR with 33-mode alone is low We have selected (b)

What can we expect from the MF with HOMs? Detection probability may increase False-alarm rate may decrease Signal-to-noise ratio may increase

Permutation test with aLIGO data Download the data around GW150914 (no signal) Shuffle the data to exclude non-Gaussian noise Include ringdown signal at 22 and 33 modes Matched filter with 22 mode only or with 22+33 modes

Analysis method Code : Matlab Data length : 1 sec Signal amplitude : given so that SN~3 with 22 mode MF Signal waveform : decay sine Mass ratio before collision : 1.4Ms/60Ms Harmonics mode : 33 only Initial phase difference : fixed to zero

If parameters for 33 mode are unknown, the ROC curve Results 1: ROC curve *ROC=Receiver Operating Characteristics Blue: 22-mode only Red: 22+33 modes detection probability detection probability Higher-order mode parameters are unknown Higher-order mode parameters are given false alarm rate false alarm rate If parameters for 33 mode are unknown, the ROC curve is not so different from the one with 22 mode only. If parameters for 33 mode were known, the ROC curve would be improved with the 33 mode.

Results 2: Signal-to-noise ratio Blue: 22+33 SNR / 22 SNR Red: mean SNR improves with the 33 mode included.

Summary and future work We investigated the possible advantage of using higher-order harmonics of QNM in the ringdown signal analysis with aLIGO Gaussian noise ROC curve does not change much if HOM parameters are not given; does improve it the parameters are given SNR improves even if the HOM parameters are not given Analysis with non-Gaussian noise is to be done

Acknowledgement This study is supported by MEXT Grant-in-Aid for Scientific Research on Innovative Areas 24103005, A04 “多様な観測に連携する重力波探索データ解析の研究”

Supplementary

KAGRA sensitivity << Old curve (calculated in 2013) The peak at 120Hz is for vertical suspension thermal noise Recoil mass is suspension from the intermediate mass New curve (calculated in 2016) >> Sapphire suspension is longer Temperature is 23K Vertical isolation by Sapphire blade spring Recoil mass is suspended from the intermediate recoil mass