ICGC 2019

				Talks Selected for Workshop -1


Title	First name		Last name	Affiliation	Abstract	Duration
Mr.	BHASKAR		BISWAS	IUCAA	We use gravitational wave (GW) and electromagnetic (EM) observations of GW170817 to constrain the extent of pressure anisotropy in it. While it is quite likely that the pressure inside a neutron star is mostly isotropic, certain physical processes or characteristics, such as phase transitions in nuclear matter or the presence of strong magnetic fields, can introduce pressure anisotropy. In this work, we show that anisotropic pressure in neutron stars can reduce their tidal deformability substantially. For the anisotropy-pressure model of Bowers and Liang and a couple of relativistic EOSs -- DDHÎ´ and GM1 -- we demonstrate that this reduction in spherical neutron stars with masses in the range of 1 to 2 MâŠ™ can be 23% to 46%. This suggests that certain EOSs that are ruled out by GW170817 observations, under assumptions of pressure isotropy, can become viable if the stars had a significant enough anisotropic pressure component, but do not violate causality. We also show how the inference of the star radius can be used to rule out certain EOSs (such as GM1), even for high anisotropic pressure, because their radii are larger than what the observations find.	Talk (12+3)

Dr.	Abhirup		Ghosh	Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam-Golm	One of the most remarkable predictions of General Relativity (GR), the no-hair conjecture, states that a stationary black hole (BH) is completely described by its mass, spin angular momentum and electric charge, which means that the frequencies of the gravitational radiation (quasi-normal-modes [QNMs]) from a perturbed BH is uniquely determined by these parameters. As a consequence, observation of multiple QNMs in the post-merger signal of a binary black hole (BBH) coalescence is a test of the Kerr nature of the BBH remnant. Based on this, we have developed and implemented a test of the no-hair theorem using spinning multipolar inspiral-merger-ringdown waveforms calibrated to numerical relativity (NR) simulations (as already developed within the effective-one-body formalism, or EOBNR), where the complex QNM frequencies are treated as free parameters and directly estimated from the data. We have further demonstrated the test on actual gravitational wave (GW) observations by the Advanced LIGO-Virgo detectors, as well as NR simulations of BBH events in Gaussian noise. Unlike other tests which try to fit a superposition of exponentially damped sinusoids to the BBH ringdown signal and hence, presume the ability to correctly estimate the time at which the GW signal starts to be dominated by the QNMs of a perturbed BH, our model, by construction, automatically includes time and phase shifts among QNMs, which also makes it well suited to consistently combine information from several observations, and thus obtain tighter constraints on possible deviations from GR.	Talk (12+3)

Mr.	Surajit		Kalita	Indian Institute of Science, Bangalore	The abstract is based on my recent arXiv paper 1905.02730. Gravitational wave is the ripple in spacetime, formed due to distortion in the curvature of the spacetime, and propagates at the speed of light. It is emitted if the system has a non-zero quadrupole moment. Recent detection of gravitational wave from nine black hole merger events and one neutron star merger event by LIGO and VIRGO shed new light in the field of astrophysics. Apart from this, there is another type of gravitational wave, known as continuous gravitational wave, which is continuously emitted at a certain frequency and amplitude. On the other hand, in the past decades, discoveries of super-Chandrasekhar white dwarfs as well as massive neutron stars were great astrophysical success, although they were inferred indirectly from other observations. Continuous gravitational wave can be one of the prominent alternate ways to detect these compact objects directly. In my presentation, I will show that magnetic field is one of the prominent physics to form super-Chandrasekhar white dwarfs and massive neutron stars. If such compact objects are rotating with a fixed angular frequency following certain conditions, they can efficiently emit gravitational radiation and these gravitational waves can be detected by some of the upcoming detectors, e.g. LISA, BBO, DECIGO, Einstein Telescope etc. This will certainly be a direct detection of super-Chandrasekhar white dwarfs as well as massive neutron stars.	Talk (12+3)

Mr.	Sayak		Datta	IUCAA	We propose a method to test the nature of the binary components in inspiral. Whether the components in a binary are a black hole or not can be probed by observing the phasing of these waves, which carry information about its mass and spin multipole moments. We use tidal heating of the binary components to distinguish black hole with other compact objects. Using these results we argue that it might be possible for LIGO and LISA to probe if the components in a binary have a horizon or not. We also discuss how our results can be used to test the No-hair theorem from the inspiral phase of such systems.	Talk (12+3)

Ms.	Nidhi		Saini	University of Delhi, Delhi	Fast Radio Bursts, also known as FRBs, are extragalactic, highly intense radio pulses of around millisecond duration. A natural explanation for an FRB can be thought of like a radio flash produced from the dying magnetosphere of a collapsing supra-massive Neutron Star (NS) as it turns into a Black Hole (BH) (Falcke & Rezzolla, 2014). We predicted that a Magnetar collapse under the Blandford-Znajek (B-Z) mechanism scenario can eventually lead to a repeating FRB. Similarly, the oscillations in the electron layer above the surface of a Strange Quark Star (SS) can also produce a repeating FRB (Das Gupta & Saini, 2018). A back-of-the-envelope calculation of a magnetar imploding into a Kerr BH shows that such an event produces a high Gravitational Wave (GW) luminosity of the order ~ 10^(56) ergs/s corresponding to a GW amplitude of ~ 10^(-18) if the FRB is at a distance of 1 Gpc. A striking similarity between the rate of FRB and supernovae Ib/c which are associated with Gamma Ray Bursts (GRBs) suggests that only those magnetars whose implosion gives FRBs, having kick velocities either aligned or anti-aligned with the spin axis of the magnetar, will be seen as GRBs. Recently, we found a negative correlation in the brightness temperature of FRBs with Dispersion Measure (DM). Moreover, the Source Count plot for the available 84 FRBs shows two distinct distribution of FRBs.	Talk (12+3)

Prof.	CS		Unnikrishnan	Tata Institute of Fundamental Research	Title: Experiments to Ascertain the True Relativistic Nature of the Propagation of Gravitational Waves and Light Abstract : The fundamental physical postulate that distinguished the theories of relativity is about the nature of the propagation of light. The general theory of relativity inherits this feature through the space-time basis of the theory. However, classic experiments involving the Michelson interferometer or cavities are two-way experiments do not directly restrict the true one-way propagation. Most one-way experiments are not capable of addressing the issue either because they are dependent on the convention in synchronizing clocks. Important space-time labelling systems like GPS and many precision tests of gravity that use light as the physical entity for tests are dependent on the fundamental postulate on the propagation of light. After showing the ambiguity arising from the synchronization convention, and some critical problems with the earlier experiments, I will describe a new class of experiments that address the one-way propagation of relativistic waves in free space and in terrestrial gravitational fields. These experiments avoid the clock synchronization ambiguity preserve the inertial nature of the reference frames used. Most importantly, these are the first experiments that employ a well-verified Galilean reference as comparison, which avoid hidden theoretical assumptions. I will present the results on the true one-way speed relative to slow inertial frames of reference. This then allows to fix the nature of propagation of gravitational waves. The results have clear implications to consistent alternatives to general relativity. Follow up experiments in preparation using pulses from a fiber femto-second laser, in an interferometric configuration, will be mentioned. References: 1. C. S. Unnikrishnan, Physics in the ‘Once-Given’ Universe, in Recent Developments in Theoretical Physics, p 99, (Eds. S. Ghosh and G. Kar, World Scientific, 2010) 2. C. S. Unnikrishnan, Int. Jl. Mod. Phys (Conf. series) 30, 1460267 (2014). 3. C. S. Unnikrishnan and G. T. Gillies, Gravitational waves at their own gravitational speed, International Journal of Modern Physics D27, 1847015 (2018). 4. C. S. Unnikrishnan, New Class Experiments on the True Relativistic Nature of the Propagation of Light, GR22 Conference, Valencia (2019).	Talk (12+3)

Ms.	Sayantani		Datta	Research Scholar	PARAMETRISED TESTS OF GENERAL RELATIVITY USING SINGULAR VALUE DECOMPOSITION.\n\nSayantani Datta, M. Saleem, K.G Arun and B. S. Sathyaprakash.\n______________________________________________________________\nLIGO observations of binary black holes have been used to test the post-Newtonian formalism by deforming one or more coefficients in the perturbative expansion of the orbital phase away from general relativity. In this work we use singular value decomposition to express the orbital phase in terms of the principal components of the post-Newtonian coefficients. The principal components are necessarily uncorrelated and hence optimally capture any deviation of the phase evolution from general relativity. Using Bayesian inference we obtain bounds on the principal post-Newtonian coefficients for binary black hole mergers GW170608 and GW151226.	Talk (12+3)

Dr.	Fatemeh		Nouri	IUCAA	Title: STUDY OF THE NONLINEAR MODE-TIDE COUPLING OF COALESCING BINARY NEUTRON STARS WITH RELATIVISTIC CORRECTIONS. Abs: Recently a new hydro instability has been introduced as a result of the nonlinear coupling of the neutron star's tidal field to pairs of p-mode and g-mode of its companion neutron star in a binary system (PG instability). This instability is important, because it can influence the inspiral phase of the neutron star binary mergers by extracting orbital energy, which leaves an observable imprint on the gravitational wave signal. So far, all the p-g instability studies have been formulated in the Newtonian perturbation theory. Because of its potential importance, the details of the instability should be further investigated, especially it is necessary to include the relativistic equations, and study their effects on the instability's criterion, growth rate and saturation. To achieve this goal, we have developed a couple of numerical codes to derive the relativistic eigenmodes of the stellar oscillations, and relativistic tidal displacement. We use these results in addition to the other relativistic corrections to compute the mode-tide coupling strength (MTCS) for different equations of state. We compare our results with the previous works, and discuss how important the relativistic effects are for the mode-tide coupling instability. Moreover, we extend our work to derive the MTCS over a reasonable range of eigenmodes to study how likely it is to trigger the instability as a result of higher-order mode-tide couplings.	Talk (12+3)

Dr.	Golam	M	Hossain	IISER Kolkata	Title: Revisiting equation of state for white dwarfs within finite temperature quantum field theory\n\nAbstract: The effects of fine-structure constant on the equation of state of degenerate matter in the white dwarfs are computed in literature using non-relativistic considerations ab initio. Given special relativity plays a key role in the white dwarf physics, such computations are therefore unsatisfactory. After reviewing the existing literature, here we employ the techniques of finite temperature relativistic quantum field theory to compute the equation of state of degenerate matter in the white dwarfs.\nIn particular, we compute the leading order corrections due to the fine-structure constant and the finite temperature. Using a fairly general consideration we show that the fine-structure constant corrections involve an apriori undetermined parameter whose determination may shed light on the underlying structure within the degenerate matter.	Talk (12+3)

Dr.	Disha		Sawant	IIT Bombay	Long duration bursts in ET:\nThe standard Gravitational waves search comprises of modeled (with waveform template bank) as well as unmodeled sources. Especially for unmodeled sources, it is still difficult to distinguish signals from instrumental noise with high confidence. Among such sources, we are focussing on non-axisymmetric Accretion Disc Instability (ADI) which leads to material spiraling into the central stellar-mass BH, emitting GWs. The strategy behind the upcoming Einstein Telescope (ET) project is to build an observatory that overcomes the limitations of current detector sites by hosting more than one GW detector. It will consist of three nested detectors, each composed of two interferometers with arms 10 kilometres long. One interferometer will detect low-frequency gravitational wave signals (2 to 40 Hz). We propose that the ADI induced GWs can be considered as excellent candidates for exploring ET capabilities.	Talk (12+3)

Ms.	Krishnendu		N V	Chennai Mathematical Institute	Title: Constraints on the binary black hole nature of GW151226 and GW170608 from the measurement of spin-induced quadrupole moments\n\n\n\n According to the â€œno-hairâ€� conjecture, a Kerr black hole (BH) is completely described by its mass and spin. In particular, the spin-induced quadrupole moment of a Kerr BH with mass m and dimensionless spin Ï‡ can be written as Q = âˆ’Îº m3 Ï‡2 , where ÎºBH = 1. Thus by measuring the spin-induced quadrupole parameter Îº, we can test the binary black hole nature of compact binaries and distinguish them from binaries comprised of other exotic compact objects, as proposed in [Krishnendu et. al., PRL 119, 091101 (2017)]. Here, we present a Bayesian framework to carry out this test where we measure the symmetric combination of individual spin-induced quadrupole moment parameters fixing the anti-symmetric combination to be zero. The analysis is restricted to the inspiral part of the signal as the spin- induced deformations are not modeled in the post-inspiral regime. We perform detailed simulations to investigate the applicability of this method for compact binaries of different masses and spins and also explore various degeneracies in the parameter space which can affect this test. We then apply this method to the gravitational wave events, GW151226 and GW170608 detected during the first and second observing runs of Advanced LIGO and Advanced Virgo detectors. We find the two events to be consistent with binary black hole mergers in general relativity. By combining information from several more of such events in the future, this method can be used to set constraints on the black hole nature of the population of compact binaries that are detected by the Advanced LIGO and Advanced Virgo detectors.	Talk (12+3)

Mr.	Nirban		Bose	IIT Bombay	Is eccentricity a crucial player in pinning down the binary black hole formation channel? \n\nCompact binary systems with black holes are primary sources of interferometric gravitational wave detectors. Though it was believed that the binaries are expected to circularize before entering the interferometric band, recent models indicate that binary sources with appreciable non-zero eccentricity are possible in the dense stellar environment like globular cluster or galactic nuclei. Different formation channel gives different distribution for the binary population. The important formation channels of eccentric binary black holes (eBBH) include dynamical encounters between binaries and a third body, or the secular Kozai Lidov mechanism where the third body induces periodic oscillations of eccentricity of the inner binary. In this work, we show that given we optimally detect the eccentric binaries one can indeed distinguish between various source eBBH distributions and hence their formation channels. We focus on stellar mass black holes and found that in the standard lambda CDM cosmology, with the sensitivity of the advanced ground based gravitational wave detectors, we expect to see a significant number of eBBH mergers in the sensitive frequency band of these detectors. The importance of the results in this work also necessitates the development of an eBBH template bank with higher eccentricities and full inspiral-merger-ringdown templates.	Talk (12+3)

Dr.	Vivek		Venkatraman Krishnan	Max Planck Institute for Radio Astronomy	Title: Gravitational dynamics of relativistic binary pulsars\n\nAbstract: Pulsars in relativistic binary systems are excellent probes of fundamental physics and binary evolution. Long term measurements of pulse arrival times from such pulsars enable theory-independent measurements of relativistic parameters that can then be used for testing different theories of gravity such as General Relativity and scalar-tensor theories of gravity. Assuming a theory of gravity, such experiments also provide highly precise measurements of neutron star masses and insights on their\nequation of state. In this talk, I will provide an introduction to pulsar timing, present recent results from long term timing campaigns of different relativistic binary pulsars including the first observations of Lense-Thirring precession in a binary pulsar system and a possible supra-massive pulsar in an eccentric binary system.	Talk (12+3)

Mr.	Shreejit	Prafulla	Jadhav	Student	LIGO data is pestered by a large number of glitches, i.e., noise transients originating from non-astrophysical sources. These transients pass the analysis pipeline by mimicking parts of the expected astrophysical signal, thereby causing false alarms. To improve the confidence in low-significance events like LVT151012, vetoing these unwanted events is very important. We use transfer learning with InceptionV3 to distinguish gravitational wave chirp signals originating from compact binary coalescences (CBCs) from other noise transients. We analyse continuous wavelet transform (CWT) maps of background events and check the probability of them being 'chirp-like'. We design a new statistic using these probability values and achieve considerable reduction in the background, thus increasing the significance of candidate events. We implement our technique as an extension of PyCBC and show that the false alarm rate (FAR) for events like LVT151012 can be improved by a factor of ∼685.	Talk (12+3)

Mr.	Vaishak		Prasad	IUCAA, Pune, India	Title: "The relation between the ingoing g ravitational waves at the horizon and the outgoing gravitational waves at null infinity" ( to be submitted) Authors:VaishakPrasad, Anshu Gupta, Badri Krishnan, Sukanta Bose Abstract: In the dynamical horizon formalism is a framework where one can study the strong gravity regime of black holes in a quasi local manner. In this formalism, there exists an exact expression for the amount of energy falling into a dynamical horizon of black hole due to the influx of gravitational waves and the dominant effect is due to the shear of the outgoing null normal at the horizon. There is also evidence from numerical relativity that the shear at the dynamical horizon is strongly correlated with the outgoing gravitational wave strain (Ashtekar, Krishnan 2004). This motivates us to study the relation between the shear of the apparent horizon with the waveform of outgoing gravitational waves at null infinity. In this work, we study non-spinning binary black hole merger simulations of various mass ratios using numerical relativity to explore the relation between the infalling gravitational waves at the apparent horizon of black holes and the outgoing gravitational waves from the system at null infinity. We study how well a particular waveform model for the outgoing gravitational waves describe the shear of the individual dynamical horizons of the black holes during the inspiral phase of the merger. Previous studies and details on Numerical Simulations: The previous study (Anshu et. al. 2018) was carried out using the numerical simulations of three quarter of the last orbit prior to the merger of a non-spinning, equal mass black hole binary focusing on the post-merger effects. Since then we have performed several additional simulations for varying mass ratios with and without spins for binary black hole systems starting 5-6 orbits prior to the merger focusing on the inspiral phase behavior as well. This study is one of the follow up works among the series of works and analysis undertaken to initiate Numerical Relativity activities in India. All the simulations have been performed on IUCAA HPC cluster ’Perseus’, using a publicly available numerical relativity code Einstein Toolkit (www.einsteintoolkit.org) .	Talk (12+3)

Dr.	Archisman		Ghosh	Leiden University	Bright and dark sirens: gravitational-wave cosmology with or without electromagnetic counterparts\n\nGW170817 with its coincident optical counterpart led to a first \standard siren\" measurement of the Hubble constant independent of the cosmological distance ladder. The Schutz \"galaxy catalogue\" approach which is expected to work in the absence of uniquely identified hosts has also started bringing in its first estimates. In this talk we report the latest results of the gravitational-wave measurement of the Hubble constant and discuss the prospects with observations during the upcoming runs of the Advanced LIGO-Virgo detector network."	Longer talk (25+5)

Dr.	Apratim		Ganguly	ICTS-IFR	Massive astrophysical compact halo objects (MACHOs) are viable compact dark matter (DM) candidates, the presence of which in the interstellar medium will lead to lensing of electromagnetic (EM)/gravitational-wave (GW) signals. Various EM lensing searches have constrained the DM density fraction, f_DM, in the form of MACHOs better than f_DM < 10^(âˆ’5) in the mass range < 10^(-16) M_sun and > 10^5 M_sun. On the other hand, LIGO-Virgo detectors (10Hz < f < 100Hz) are well suited to probe MACHOs in the mass range 10 âˆ’ 10^5 M_sun via GW lensing. The lensed lens waveform will have a frequency dependent magnification/demagnification in the wave-optics limit (Î»_(GW) âˆ¼ R_(Sch)^(lens) ), which is true for MACHOs. In this talk, we will discuss how the search of lensing signature in GW events observed by LIGO-Virgo can be used to put better constraints on f_DM.	Talk (12+3)

Dr.	Sukanta		Bose	IUCAA, WSU	I will talk about how gravitational wave observations of compact binaries with neutron stars can be used to constrain neutron star equation of state. It is based on: https://arxiv.org/abs/1705.10850; https://arxiv.org/abs/1904.04233 .	Longer talk (25+5)

Mr.	SUNIL		CHOUDHARY	IUCAA	The LIGO detector data contains many noise artefacts apart from the GW signals. We look at the data analysis techniques that help us identify the signal buried in noise. Matched filtering is a method that uses cross-correlation to detect a hidden signal in noisy data. This is done by cross-correlating detector data with thousands of existing templates over the entire parameter space and looking for the highest matched-filtering value, denoting the possible existence of a GW (Gravitational Wave) signal. A large matched filtering value is not sufficient for claiming a detection as large noise events and glitches can also produce high values. The traditional chi-square test or power chi-square is a statistic that helps in differentiating a astrophysical signal from a glitch. This test works well in low and intermediate mass range BBH signals. However, we show that as we go above intermediate mass range BBH systems, traditional chi-square test fails to differentiate between the glitches and the astrophysical signals. More specifically the glitches which escape the filter of traditional chi-square are blip glitches, very sharp high power transient noises.\nIn our study we use the generic chi-square formalism to formulate a new chi-square statistics that is sensitive to blip-glitches. First we show that blip glitches can be successfully mimicked by the sine-gaussian waveforms. Then with the help of sine-gaussian waveforms as our basis we develop a chi-square statistics which successfully distinguishes the high mass BBH signals from the blip glitches.	Talk (12+3)

Dr.	Aditya		Vijaykumar	International Centre for Theoretical Sciences, Bengaluru	Advanced gravitational-wave (GW) observatories are expected to observe thousands of binary black hole mergers in the next few years, and the detection rates will go up by several orders of magnitude with the advent of third generation observatories like the Einstein Telescope and Cosmic Explorer. The reconstructed three-dimensional location of these mergers will probe the large-scale structure of the Universe, analogous to the current galaxy surveys using optical telescopes. GW and optical surveys are likely to provide complementary information --- GW observations are likely to access very large redshifts ($z sim 10-15$) inaccessible by optical telescopes, although with much poor precision on the source location. We explore the possibility of probing large scale structures from the correlation function and power spectrum of the distribution of binary black hole mergers using the second and third generation of gravitational-wave observatories.	Talk (12+3)

Dr.	Rakesh		Kabir	University of Delhi	The mainstream technique used for signal detection in gravitational wave data is match-filtering, which uses waveform templates. This technique is computationally expensive. Here we use wavelet transforms and convolution neural networks (CNNs) to train a model which is capable of identifying and extracting gravitational wave signals in the data from Advanced LIGO. Further, the extrapolation ability of the trained CNNs has been studied by testing on simulated signals (using available waveform approximants) of different eccentricities, spins and signal strengths than they were trained on.\n\nNote: This is re-submission of my abstract after correction of typographical errors.	Talk (12+3)

Mr.	Varun		Srivastava	Syracuse University	We discuss how to optimize the third-generation gravitational-wave detector to maximize the range to detect core-collapse supernovae. Based on three-dimensional simulations for core-collapse and the corresponding gravitational-wave waveform emitted, the corresponding detection range for these waveforms is limited to within our galaxy even in the era of third-generation detectors. The corresponding event rate is two per century. We find from the waveforms that to detect core-collapse supernovae with an event rate of one per year, the gravitational-wave detectors need a strain sensitivity of 3$times10^{-27}~$Hz$^{-1/2}$ in a frequency range from 100~Hz to 1500~Hz. We also explore detector configurations technologically beyond the scope of third-generation detectors. We find with these improvements, the event rate for gravitational-wave observations from CCSNe is still low, but is improved to one in twenty years.	Talk (12+3)

Dr.	Shasvath		Kapadia	International Centre for Theoretical Sciences (ICTS-TIFR)	Estimating the rates of compact binary mergers from gravitational-wave (GW) data produced by the LIGO-Virgo network of ground based detectors is an important science target of the LIGO-Virgo collaboration (LVC), given that such rates could help inform the construction of models of stellar mass binaries. In this talk, we describe the Poisson-statistics-based formalism used to compute these rates. From data acquired during the first and second observing runs (O1 and O2) and analyzed by the GstLAL pipeline, we estimate posterior probability distributions on the astrophysical rates of mergers for three distinct classes of compact binaries, as well as assign source-specific astrophysical probabilities to candidate events. We find the rate of binary black hole mergers and binary neutron star mergers, at 90% confidence, to be 9âˆ’100/Gpc^3/yr and 97âˆ’3140/Gpc^3/yr, respectively, and a 90% upper limit on the rate of neutron star black hole mergers to be 610/Gpc^3/yr.	Talk (12+3)

Dr.	Muhammed		Saleem	Chennai Mathematical Institute	Title: Constraining the properties of electromagnetic counterparts of binary neutron star mergers. \n\nPeople: M. Saleem, Resmi Lekshmi, K.G. Arun, Sreelakshmi Mohan.\n\nAbstract: The electromagnetic (EM) follow-up studies of the binary neutron star (BNS) merger GW170817 showed that BNS mergers can be accompanied by relativistic structured jets. As per the recent merger rate estimates obtained using the Advanced LIGO-Virgo observations, tens to hundreds of BNS merger detections are expected over next few years. Here, assuming the short GRBs to have Gaussian structured jets, we investigate the detectability of prompt gamma ray emission as counterparts to the gravitational wave detections of BNS mergers and obtain the joint BNS-GRB detection rates. We show how the detection or non-detection of a GRB counterpart with a BNS merger detection will lead to constraints on the intrinsic GRB properties. We use this method to obtain bounds on the properties of a possible GRB counterpart of the recent LIGO-Virgo candidate S190425z.	Talk (12+3)

Dr.	Arman		Tursunov	Silesian University in Opava, Czech Republic	Title: Fifty years of energy extraction from rotating black holes Abstract: A fascinating process mining the rotational energy of black hole heralded by Roger Penrose half a century ago has risen today in its magnetically empowered version of mid 1980s from a purely thought experiment of academic interest to a realistic powering mechanism for various high-energy astrophysical phenomena. I will show that magnetic Penrose process (MPP) operates in three regimes of efficiency, depending on the magnetization and charging of spinning black holes in astrophysical settings. This can make MPP responsible for powering engine of such phenomena as ultra-high-energy cosmic rays, relativistic jets, fast radio bursts, AGNs, etc. Further, it leads to a number of important observable predictions, which I will discuss.	Talk (12+3)

Ms.	SRASHTI		GOYAL	International center of theoretical sciences Bangalore	Extracting gravitational wave polarizations from strongly lensed signals of the binary black hole mergers.\n\n\n\nAccording to general theory of relativity, gravitational waves (GWs) can have only two independent polarizations. However, in a generic metric theory of gravity, GWs can have up to six polarizations (tensor, vector and scalar modes). Thus, extracting the polarization states of GWs is a powerful test of general relativity. The present day three detector LIGO-Virgo network is not capable of breaking the degeneracies between these polarizations. However, if the GWs undergo strong lensing by galaxies or galaxy clusters, the same event can be observed multiple times, with a time delays of minutes to months between the observations. This is equivalent to observing the same event with additional detectors, which will break the degeneracies between different polarization states. Here we use a Bayesian model selection method to constrain the presence of additional polarizations using GW observations of strongly lensed binary black hole mergers.	Talk (12+3)

Dr.	Kailash	Chandra	Sahu	Space Telescope Science Institute	Title: Detecting Isolated, Stellar-Mass Black Holes through Relativistic Deflection\n\nAbstract: All stars with initial masses of larger than 20 solar mass are expected to end their lives as black holes. Yet, not a single isolated\nblack hole has been unambiguously detected to date. Relativistic deflection is the only available technique capable of detecting isolated black holes and measuring their masses. I will discuss the technique, and our two HST programs underway aimed at the first detections of isolated, stellar-mass black holes through this technique.	Talk (12+3)

Mr.	Amit		Reza	Indian Institute of Technology Gandhinagar (IITGN)	Highly faithful interpolation of gravitational-wave signals from compact binaries using radial basis function\n\nAyatri Singha, Amit Reza, Anand. S. Sengupta\nIIT Gandhinagar, Gujarat - 382355\n\nDevelopment of a computationally efficient numerical framework to perform parameter estimation for reconstructing compact-binary gravitational wave (GW) sources is crucial. Evaluating the posterior probability distribution of the source parameters involves computing millions of waveforms over the parameter space which are then used to evaluate the likelihood ratio. Existing waveform interpolation schemes such as Chebyshev interpolation, rely on a grid-based sampling of the parameter space. Such schemes do not scale well for high-dimensional parameter spaces as the number of sampled points increases steeply with the dimensionality of the parameter space. We present an efficient numerical interpolation scheme based on radial basis functions where one can randomly sample the parameter space for input points. We show that in such a strategy the required number of input waveforms for interpolation is moderate for higher dimensional parameter spaces and is hence computationally efficient. Also, this scheme can be directly applied for interpolating the likelihood function directly and thus be a useful tool for rapid parameter reconstruction. We illustrate this new interpolation scheme using non-spinning TaylorF2 waveforms over the 2D chirp-mass and symmetric mass ratio parameters. In this case, we find a very high level (> 0.99) of faithfulness for the interpolated waveforms. The method can be extended for the likelihood time-series interpolation and the results are also shown.\n\nKeywords: Gravitational waves, Singular value decomposition, Radial basis function	Talk (12+3)

Mr.	Soumen		Roy	IIT Gandhinagar	Title:- Detection of non-quadrupole modes of gravitational waves from multiple inspiralling blackholes\n\nAuthors:- Soumen Roy, Anand S. Sengupta, and K. G. Arun\n\nInstitute:- Indian Institute of Technology Gandhinagar, Gujarat 382355, India\n\nAbstract:- The measurement of non-quadrupole modes of gravitational wave signals from compact binary coalescences is of central importance for astrophysics and fundamental physics with wide-ranging implications. As the non-quadrupole modes carry much less power compared to the dominant quadrupole mode and visible only for binaries consisting of unequal masses with an orbital geometry that is not face-on, their detection is very challenging. We present a novel method to combine the energy from multiple events to enhance the signal-to-noise ratio of the subdominant modes of the inspiral regime of the signal and thereby increase the chances of their detection. The stacking is done using the time-frequency representations of the data, utilizing the set of intrinsic parameters (mass, spin, and orbital parameters) inferred from the measurement of the dominant mode. Our studies suggest a â‰¥ 99% chance of detecting these subdominant modes from O(100) events seen in advanced LIGO, at a false alarm probability of 1%.	Talk (12+3)

Dr.	Anshu		Gupta	Consultant, Gravitational Wave Physics Group, IUCAA, Pune	Title: Numerical simulations of general relativistic rotating stars in 3D: extraction of gravitational radiation through excited quasi-radial oscillation modes. Abs: For a non-rotating object, one of the main modes describing the internal structure of the body is radial oscillations. In the presence of rotation, there are no radial modes but quasi-radial modes. Studies have been done earlier for quasi-radial modes under Cowling approximation i.e. while keeping spacetime fixed. In the current study we have performed the full general relativistic hydro-dynamical time evolution numerically, using the initial data for a rotating neutron star. Extraction of the fundamental modes and of its overtones are carried out for the multiple sequences of constant angular momentum using the method of 2D-FFT data [1] at the several frequency peaks observed in the FFT of central density. Further, gravitational radiation associated with quasi-radial oscillations (l=0 mode of fundamental frequency) is computed based on the approach undertaken in [2]. Results and methods would be presented.	Talk (12+3)