Isolated NSs as sources of transient GWs. STAMP pipeline - Data analysis methods

Transcription

1 Isolated NSs as sources of transient GWs Intermediate duration ( long bursts ) GWs, O(s) - O(weeks) STAMP pipeline - Data analysis methods Searching for transient gravitational waves from isolated neutron stars using STAMP Stefanos Giampanis University of Wisconsin - Milwaukee gstef@gravity.phys.uwm.edu Abstract Isolated (non-accreting) neutron stars (NSs) are expected to emit continuous gravitational waves (GWs) via a number or mechanisms (non-axisymmetric distortions, free precession, velocity perturbations in the star s fluid). Transient GWs from isolated NSs are also plausible via similar mechanisms. These include GWs due to instabilities occurring at early stages in the NSs evolution, such as r-modes and bar-modes; GWs due to magnetically induced deformations in young fast rotating magnetars; and GWs associated with electromagnetic glitches. Depending on the process the duration of the GWs can vary from minutes to weeks and possibly months. STAMP, the Stochastic Transient Analysis Multi-detector Pipeline, is a unique tool for searching for such signals in data from current and future generation gravitational wave detectors. The STAMP Pipeline STAMP, the Stochastic Transient Analysis Multidetector Pipeline is a cross-correlation based multidetector data analysis pipeline designed for detecting long gravitational-wave transients [1]. STAMP uses time-frequency patterns in the cross-correlation power between multiple detectors. These transients can span any duration from seconds to weeks. STAMP does not assume a signal model but, instead, employes different pattern-recognition techniques. Secular bar mode instabilities Newly formed rapidly rotating neutron stars (NSs) can become dynamically or secularly unstable via bar-mode (l = m = 2) instabilities driven by gravitational radiation. After the core collapse of a massive star or accretion induced collapse of a white dwarf, the proto-ns settles into an axisymmetric secularly unstable equilibrium state if the ratio of its rotational energy T to the gravitational potential energy W, β = T/ W, exceeds a threshold β > βsec.14. The star is dynamically unstable if β > βdyn.27. Dynamic instabilities have extremely short growth times (O(ms)). Secular instabilities, on the other hand, are interesting GW sources for STAMP. Depending on β, the NS s mass, radius GWPAW, Milwaukee WI, January 26-29, 211. LIGO-G11137 and polytropic index, the growth time of a secularly unstable bar mode can be approximately written as [2] τgw M1.4 3 R4 1(β βsec) 5 s, for < β βsec 1. The larger β is the shorter the growth time of the instability; hence the stronger the associated GW emission. The GW components can be expressed as [2, 5]) h+ = h[f(t); fmax,m,r]cosφ(t)(1 + cos 2 θ)/2 (1) h = h[f(t); fmax,m,r]sinφ(t)cosθ (2) where M, R are the mass and radius of the NS, Φ is the GW phase and θ is the angle between the rotation axis of the NS and the line of sight from earth. h [strain] x x 1 22 f [Hz] t [sec] Figure 1: Example of a GW from a 1.4 solar mass NS at distance d =8kpc, with a 2 km radius, polytropic index n =1and θ =3. The GW emission initially occurs at 15 Hz and lasts O(1) sec. Top inset: frequency evolution of GW. f (Hz) time (s) Figure 2: Example of STAMP s SNR map using Fig. 1 s synthetic waveform and noise similar to LIGO S5 s run. h + h x SNR r-mode instabilities Like bar-modes the instability in r-modes is driven by gravitational radiation reaction (CFS instability); the GW emission mechanism is due to a time varying current quadrupole; r-modes are (always) secularly unstable; the emitted GWs are quasi-sinusoidal at frequencies (l 1)(l +2) fr ν l=2 = 4 ν, (3) l +1 3 where ν is the spin frequency of the NS. The growth time of r-modes can vary over several orders of magnitude and is very sensitive to temperature and the dissipative effects of viscosity. Owen et. al.[3] estimate an initial linear growth phase 1 3 sec and a slowly varying frequency 1kHz. After that initial phase the emitted GW (as the NS is spinning down due to gravitational radiation) decreases in amplitude and frequency over a much longer time. Young magnetars Magnetars are NSs with high magnetic fields. Their spin down and bright emission activity is believed to be powered by their magnetic field. In the presence of poloidal/toroidal magnetic fields the NS becomes oblate/prolate with an magnetically induced ellipticity Q [6]. 2 Bpole(G) Q k 1 4 (4) 1 16 k O(1) depends on the EOS, Bpole is the amplitude of the dipolar surface magnetic field at the pole. In an axisymmetric NS with a quadrupole ellipticity Q if the magnetic axis does not coincide with the rotation axis, deviating by an angle α, the associated GW emission occurs at frequency ν, the NS spin frequency, if α is small. The GW amplitude h is given by h 4G I Q sin α (5) rc 4(2πν)2 where r is the distance to the NS, c is the speed of light and G is the Newton s constant. Due to dissipative processes α goes to zero as the rotation rate decreases due to the NS spinning down emitting GWs. This damping timescale can vary from months to years depending on the magnetic field, induced ellipticity, rotational period and dissipation process. The transient GW can spend a significant portion of its lifetime within the frequency range of GW detector if the young NS is born rotating at high frequencies (.1 1 khz). Transient GWs associated with NS glitches Sudden spin-ups (more commonly referred to as glitches ) are observed in the emitted EM spectrum of several known NSs. A two fluid model, consisting of an interior normal fluid, a superfluid and a crust is normally employed in phenomenological studies of the observed glitches [4]. Prix et. al. [7] assume a differentially rotating superfluid and crust and calculate the available kinetic energy ( glitch energy) when non-differential rotation is restored. The latter is hypothesized to occur at the time of a glitch while a differential rotation is built up between two glitches. Whether the available glitch energy is transferred from the superfluid to the crust exerting a strain onto it (hence an observed EM glitch ) or is directly channeled in GW emission (via an internal instability) remains a matter of study. Nevertheless, the emitted GWs are of transient nature with duration times comparable to observed relaxation times of EM glitches. The GW signal is quasi-sinusoidal with a well-defined slowly varying frequency. References [1] E. Thrane et. al. arxiv: v1 [2] D. Lai and S. Shapiro, APJ, 442, (1995) [3] B. Owen et. al., Phys. Rev. D 58, 842 (1998) [4] A. G. Lyne, S. L. Shemar, and F. G. Smith, MNRAS 315, (2) [5] D. Lai, arxiv:astro-ph/1142v1, (21) [6] L Gualtieri, R Ciolfi and V Ferrari, arxiv: v1 [7] R. Prix, S. Giampanis, and C. Messenger, LIGO-P112

2 NASA EM Followup of LIGO-Virgo Candidate Events Lindy Blackburn for the LIGO Scientific Collaboration and Virgo Collaboration NASA Goddard Space Flight Center We describe an offline, targeted search of archive data from several NASA high-energy EM instruments for prompt and afterglow EM signals about the time of LIGO-Virgo GW events. FERMI GBM 2 kev-4 MeV 65% FOV RXTE ASM 1-1 kev 3% FOV 4 CHAPT LIGO-Virgo trigger time and sky location SWIFT BAT 2 kev-15 kev 15% FOV FERMI LAT 2 MeV-3 GeV 2% FOV

3 Low-latency Selection of Gravitational-wave Event Candidates for Wide-field Optical Follow-up Observation! Amber Stuver for the LSC and the Virgo Collaboration! LIGO & Virgo have been recently operated as a multi-messenger event generator.! Humans do final event event vetting and decision making regarding EM observing requests.! This poster presents the EM follow-up infrastructure from event generation and focusing on the human vetting process. LIGO-G111-v3!!!!!!!!

4 Localization of gravitational wave sources with network of advanced detectors M. Drago for the cwb group Joint observations with GW detectors, electromagnetic (EM) telescopes or neutrino detectors can allow a multi- messenger investigation of the astrophysical source and may improve the confidence of the first direct detection of GWs. We investigate the direction resolution of GW detector networks using Coherent Waveburst algorithm, considering simulated data of 2 nd generation interferometers: Advanced LIGO, Advanced Virgo, Large Cryogenic Gravitational Telescope and LIGO- Australia. The major challenge is to establish unambiguous association between a GW signal and possible EM counterpart pointing to the GW candidate source, with an uncertainty within the EM instrument field of view (typically < few square degrees) performing the sky localization in real time with low latency to allow the observations of EM transients arxiv: [astro- ph.im] 26 Jan 211

5 Rapid Sky Localization from Partial Monte Carlo Markov Chains.4 True!! final (deg) Runtime (hours).4 True!! final (deg) Runtime (hours) B. Farr, V. Raymond, M. van der Sluys, I. Mandel, W. Farr, V. Kalogera, C. Röver, N. Christensen

6 Sky Localization of NS-NS and NS-BH Inspirals With GW Interferometer Networks. MCMC analysis of sky localization for astrophysical compact binary populations using different networks (aligo, Virgo, LCGT, AustralianLIGO). AustralianLIGO dramatically reduces sky errors (~ by a factor of 5). For specific trigger scenarios, 5% of NS-NSs are localized: < 5 sq. deg. with networks including AustralianLIGO. < 15 sq. deg. with only aligo+virgo. Poster #28 Samaya Nissanke (JPL/Caltech), Neal Dalal (CITA), Daniel Holz (LANL), Scott Hughes (MIT), Jon Sievers (CITA).

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8 Summed Parallel Infinite Impulse Response (SPIIR) Filters For Low-Latency Gravitational Wave Detection Shaun Hooper1, Linqing Wen1, David Blair1, Jing Luan2, Shin Kee Chung1 and Yanbei Chen2 1 The University of Western Australia, 2California Institute of Technology Prompt Optical Follow-Up Inspiral Waveform as a Summation of Sinusoids ( a)... (b)... (c ) (d) (e ) Time-Domain GW Detection Method FIR yk = kj= N bj xk j Computationally expensive IIR yk = a1yk 1 + bxk Computationally cheap Real Time Filter Output same as Matched Filter 1 9 IIR filter output Matched filter output SNR Shaun Hooper et. al 15 SPIIR Filters For Low-Latency Gravitational Wave Detection (LIGO - G113) t τ c (ms) 1 15 Mail: hoopes1@student.uwa.edu.au

9 Compact binary coalescence searches with low latency: why and how (P31, M1) P. Ajith, K. Cannon, B. Daudert,. Fotopoulos, M. Frei, C,. Hanna, S. Hooper, D. Keppel, A. Mercer, S. Privitera, A. Searle, L. Singer, A. Weinstein Low-latency GW triggering will aid rapid EM followup Techniques: principal component analysis conditional SNR reconstruction multi-rate filtering short FFTs streaming architecture

10 gstlal Burst search with gstreamer pipeline! "#$ GWPAW211

11 Generate bank of templates Matchfilter data Generate bank of templates Matchfilter data Data-find H1 H2 L1 V1 Coincidence test: time, waveform parameters Candidate event (pass) Coherent stage: phase and amplitude consistency check Generate bank of templates Matchfilter data Generate bank of templates Matchfilter data Discard (fail) Coherently searching for perturbed black-hole ringdown signals with a network of gravitational-wave detectors Coherently searching for perturbed black-hole ringdown signals with a network of gravitational-wave detectors Dipongkar Talukder and Sukanta Bose Department of Physics and Astronomy, Washington State University, Pullman, WA , USA Abstract We present results in Gaussian data from a template-based multi-detector coherent search for perturbed-black-hole ringdown signals. Like the past coincidence ringdown searches in LIGO data, our method incorporates knowledge of the ringdown waveform in constructing the search templates. Additionally, it checks for consistency of signal amplitude and phase with the signals times-of-arrival at the detectors. The latter feature is common to both of our method and the CoherentWaveBurstalgorithm,andcanhelpbridgethegapinperformance between the coincidence search and the coherent WaveBurst search for ringdown signals. [LIGO Document Control Center Number: LIGO-G1136-x.] Gravitational waves from perturbed black holes Several ground-based interferometric observatories, such as LIGO and Virgo, have collected data so that astronomers can search for gravitational-wave (GW) signals in them. One such signal is that arising from a perturbed black hole, which can result from the coalescence of a compact binary. This signal is initially in the form of a superposition of quasi-normal modes. However, at late times the waveform, which is known as a ringdown, isexpected to be dominated by a single mode. The optimal method for searching such a signal buried in detector noise is to match-filter the detectors output with theoretically modeled waveforms. The coherent network statistic is optimal for detecting these signals in stationary, Gaussian noise [1, 2]. But in real noise, which is non-gaussian and nonstationary, additional discriminators of noise artifacts are required for obtaining a (near-)optimal statistic. Here, we describe a hierarchical method for coherently searching ringdown signals in a network of detectors that is aided by such discriminators. The ringdown waveform The central frequency and the decay time of the quasinormal mode oscillation can be predicted with good accuracy by black-hole perturbation theory. The plus and cross polarizations of a ringdown waveform can be expressed in terms of the central frequency f and the quality factor Q as h+(t) = A r (1 + cos2 ι) e πf t Q cos(2πft), h (t) = A t r 2cosιe πf Q sin(2πft), where A is the amplitude, r is the distance from the source and ι is the inclination angle of the source. We consider here only the dominant mode i.e, the most slowly damped mode, l = m =2. The strain produced in the detector is then h(t) =h+(t)f+(θ, φ, ψ)+h (t)f (θ, φ, ψ), where F+, are the detector antenna-pattern functions, with ψ being the wave-polarization angle and (θ, φ) being the sky-position of the source. Asearchbasedonmatched-filtering In GW data analysis, the data from multiple detectors is match-filtered with templates derived from theoretical waveforms to test the presence or absence of signals in the data. Filtering the data s(t) with a template h(t;µi) characterized by the source parameters µi yields the signal-tonoise ratio (SNR) statistic given by ρ(h) = s, h, h,h where s, h denotes the noise-weighted scalar product of the data and the template. Far from the source, the ringdown template can be expressed as h(t) =e πf t Q cos(2πft ϕ). For each template, triggers that have SNRs greater than apre-definedthresholdareretained. Thesetriggersare used for determining coincidence across different detectors. This method is the so-called coincidence multidetector search [3-5]. Figure 1: A schematic diagram of the coincidence and coherentstages in the ringdown search pipeline. Coherent statistic Unlike the coincident multi-detector search statistics that have been employed so far, the coherent statistics are different in the sense that they check for the consistency of the signal amplitudes and phases in the different detectors with their different orientations and with the signal arrival times in them [1, 2]. The coherent search statistic for two coaligned detectors with different noise power spectral density is the coherent SNR, given by ρ coh = C1 σ1 + C2 σ2, σ1 2 + σ2 2 (ρ1σ1) 2 +(ρ2σ2) 2 +2(ρ1σ1)(ρ2σ2)cos(Φ1 Φ2), where σ I is the template-norm and C I is the matched-filter output against a circular-polarization template in the Ith detector. For non-stationary artifacts, however, additional discriminators are required. One such construct is the null-stream statistic [6], which is η = C1/σ1 C2/σ2 1/σ /σ2 2 for two co-aligned detectors. For more detectors at different sites and with different orientations, the above expression will involve antenna factors and time-delays. Coincidence statistic Slides Injections H1L1 doubles in double time Coherent statistic Figure 2: The scatter plot of coincidence and coherent statistic values for injection triggers, denoted by red pluses, and background (or slide) triggers, represented by black asterisks. Here we present only the weak injections. All background triggers have been retained. Note that there are more found injections that are louder than the loudest background trigger when the statistic used is the coherent one instead of the coincidence one.. Results To study the utility of the coherent statistics, we ran the ringdown search pipeline (see Fig. 1) on the NINJA-2 (simulated) data set for the 4km-long LIGO detectors in Hanford (H1) and Livingston (L1) and for the duration of approximately a week. A total of 226 signals were present in the simulated data, of which 217 were found by the ringdown pipeline. A total of 143 background triggers, obtained through time-slide experiments, were found. Figure 2showsascatterplotofthecoincidenceversuscoherent statistic for the found injection and slide triggers. In Fig. 3 we compare efficiency of finding injection triggers using coincidence and coherent searches. Note that only amplitude consistency is applied in this analysis. Fraction of injections found louder than loudest background Efficiency of injection finding in the H1L1 doubles in double time 1 Coherent search Coincidence search Injected distance (Mpc) Figure 3: Here we compare the efficiencies of finding signals in H1- L1 using coincidence and coherent searches. All injection and background triggers were found in (double) coincidence in H1 and L1. Note that the average (vertical) error bar in each distance bin is.25. Discussion As discussed above, we show that the coherent search performs better than the coincidence search at least in stationary, Gaussian data. We expect its performance to be boosted for triple-site searches, where the phase consistency test can be applied. We will do so next [7], once the coincidence stage of the three-site search has been implemented. There we plan to compare the performance of the coherent ringdown search with that of the Coherent Wave- Burst [8]. Acknowledgements We thank Paul Baker, Sarah Caudill, Neil Cornish, Jolien Creighton, Gregory Mendell and Fred Raab for helpful discussions. This work was supported in part by NSF grant PHY References [1] S. Bose, A. Pai and S. V. Dhurandhar, Int. J. Mod. Phys. D 9, 325(2),[arXiv:gr-qc/21]. [2] A. Pai, S. Dhurandhar and S. Bose, Phys. Rev. D 64, 424 (21) [arxiv:gr-qc/978]. [3] J. D. E. Creighton, Phys. Rev. D 6, 221 (1999) [arxiv:gr-qc/99184]. [4] B. P. Abbott et al. [LIGO Scientific Collaboration], Phys. Rev. D 8, 621(29)[arXiv: [gr-qc]]. [5] Lisa M. Goggin, Phd thesis, Caltech, May 28 [arxiv: [gr-qc]]. [6] Y. Gürsel and M. Tinto, Phys. Rev. D 4, 3884(1989). [7] D. Talukder et al., work in progress. [8] S. Klimenko, I. Yakushin, A. Mercer and G. Mitselmakher, Class. Quant. Grav. 25, 11429(28). Current (coincidence) search does not check for the consistency of the amplitudes and phases of the signals in the detectors due to a putative ringdown source with their observed time-delays. What happens to the performance of the search when these checks are applied? (Dipongkar Talukder and Sukanta Bose) 1/1