ICGC 2019

				Posters Selected for Workshop-1



Title	First name		Last name	Affiliation	Abstract
Mr.	Indu	Kalpa	Dihingia	IIT Guwahati	We study dissipative two-temperature accretion flow around a Kerr black hole following semi-relativistic approach. We consider flow to be consist of ions and electrons. The ions heat up due to the viscous heating and transfer a part of its energy to the electrons via Coulomb coupling. Finally, electrons radiate these energies via different radiative processes. We consider the toroidal magnetic field to be the dominating magnetic field component in the accretion disk. So, along with the bremsstrahlung, flow is associated with the synchrotron radiations, and the Comptonization process further strengthens the synchrotron radiations. We calculate the global transonic accretion solution and enact the transonic shock solutions to calculate the emission spectrum of the accretion disk. Initially, we calculate the individual emission spectrum for every radiative process and combine them to obtain the corresponding total emission spectrum and the spectral index of the accretion disk. We study the dynamics of shock location $(X_s)$, compression ratio $(R)$, and the spectral index with accretion rate $(dot{m})$ and magnetic field strength and find ample pieces of evidence that these two mechanisms are responsible for the observed spectral state transition in astrophysical sources.

Dr.	Indrani		Banerjee	Indian Association for the Cultivation of Science	Title: Decoding signatures of extra dimensions and estimating spin of quasars from the continuum spectrum\n\nAuthors: Indrani Banerjee , Sumanta Chakraborty and Soumitra SenGupta\n\nAbstract: Continuum spectrum emitted by the accretion disk around quasars hold a wealth of information\nregarding the strong gravitational field produced by the massive central object. Such a strong gravity\nregime is often expected to be the ideal place to look for deviations from general relativistic predictions.\nOne possible avenue, which may lead to deviations from general relativity, corresponds to the presence\nof extra dimensions. Since extra dimensions are well motivated from the perspective of high energy\nphysics, it is instructive to investigate the effect of more than four spacetime dimensions on the black\nhole continuum spectrum, an effective astrophysical probe to the strong gravity regime. To explore\nsuch a scenario, we compute the optical luminosity emitted by a thin accretion disk around a rotating\nsupermassive black hole albeit in the presence of extra dimensions. The background metric resembles\nthe Kerr-Newman spacetime of general relativity where the tidal charge parameter, inherited from\nextra dimensions, can also assume negative values. The theoretical luminosity computed in such a\nbackground is contrasted with optical observations of eighty quasars. The difference between the\ntheoretical and observed luminosity for these quasars is used to infer the most favoured choice of\nthe rotation parameter for each quasar and the tidal charge parameter. This has been achieved by\nminimizing/maximizing several error estimators, e.g.,chi-squared , Nash-Sutcliffe efficiency, index of agreement\netc. Intriguingly, all of them favour a negative value for the tidal charge parameter, a characteristic\nsignature of extra dimensions.

Mr.	Subhajit		Barman	Indian Institute of Science Education and Research Kolkata	Title: "Perturbative approach to the entanglement entropy and the area law". Abstract: "Among many derivations, the area law of entanglement entropy is frequently understood using the concept of coupled harmonic oscillators, where the Gaussian nature of the ground state wave-function simplifies the computation and provides the eigenvalues of the reduced density matrix. However, not all quantization procedures give these Gaussian wave-functions, and polymer quantization is one of them. Therefore, we have treated coupled harmonic oscillators perturbatively and obtained the area law of entanglement entropy in both Fock and polymer quantization. We have observed that for two coupled harmonic oscillators the entanglement entropy decreases in high-frequency regimes in polymer quantization keeping the coupling strength fixed, while in Schrödinger quantization it is unchanged. On the other hand, the effect of these high-energy regimes lowers the slope of the area curve in polymer quantization."

Dr.	Arun	Kumar	Pandey	Department of Physics and Astrophysics,Delhi University North Campus, University Road	It is known that there is asymmetry in the number density of different neutrino species in the standard model of particle physics. In the presence of the asymmetric, distribution of the number densities, turbulence is created which in turn leads to the production of the magnetic fields. These generated magnetic fields show helical behavior. Because of the helical nature, magnetic energy transfers from small scale to large scale. Therefore, we predict that these magnetic fields generated by this\nmechanism may be one of the possible tools to produce the magnetic fields. Since these magnetic fields could create a non-zero anisotropic energy-momentum tensor, they can act as a source for the Gravitational waves (GWs). We have shown that the GWs generated via this mechanism will be detected in experiments like IPTA.

Ms.	Bhaswati		Mandal	Indian Association for the Cultivation of Science	Extra dimensions, which led to the foundation and inception of string theory, provide an elegant approach to force-unification. With bulk curvature as high as the Planck scale, higher curvature\nterms, namely f (R) gravity seems to be a natural addendum in the bulk action. These can not only pass the classic tests of general relativity but also serve as potential alternatives to dark matter and dark energy. With interesting implications in inflationary cosmology, gravitational waves and particle phenomenology it is worth exploring the impact of extra dimensions and higher curvature in black hole accretion. Various classes of black hole solutions have been derived which bear non-trivial imprints of these ultraviolet corrections to general relativity. This in turn gets engraved in the continuum spectrum emitted by the accretion disk around black holes. Since the near horizon regime of supermassive black holes manifest maximum curvature effects, we compare the theoretical estimates of disk luminosity with quasar optical data to discern the effect of the modified background on the spectrum. In particular, we explore a certain class of black hole solution bearing a striking resemblance with the well-known Reissner-NordstrÃ¶m de-Sitter/anti-de Sitter/flat spacetime which unlike general relativity can also accommodate a negative charge parameter. By computing error estimators like chi-square, Nash-Sutcliffe efficiency, index of agreement, etc. we infer that optical observations of quasars favor a negative charge parameter which can be a possible indicator of extra dimensions. The\nanalysis also supports an asymptotically de Sitter spacetime with an estimate of the magnitude of the cosmological constant whose origin is solely attributed to higher curvature terms in higher dimensions.

Ms.	SHILPA		SARKAR	ARYABHATTA RESEARCH INSTITUTE OF OBSERVATIONAL SCIENCES (ARIES), NAINITAL	Title : Two-temperature advective transonic accretion flows around black holes. Abstract : Accretion onto black holes are one of the most energetic processes happening in the Universe. This process provides us with the explanation of the huge amount of energy liberated and high luminosities observed in AGN's, X-ray binaries etc. Modeling of these accretion-flows is necessary to obtain a proper picture of the processes and phenomena going on. Since electrons are the ones which radiate via processes like synchrotron, bremsstrahlung and inverse-Compton scattering, therefore the electron gas and proton gas, present in the ionized plasma of the accretion disk, are supposed to settle down at two different temperatures, hence the name two-temperature. Not much work has been done in two-temperature accretion flows, so we addressed this problem in greater details in the pure general-relativistic regime. The problem with two-temperature flow is that, there is one more variable than the number of equations. Assuming axis-symmetry, we have four equations of motion, while there are five flow variables: v_r, v_\phi, electron temperature (Te), proton temperature (Tp) and density. Solving the equations of motion for a given set of constants of motion, we find that no unique solution exists unlike in the case of one-temperature flows or in other words the solutions are degenerate. So, for different combinations of the flow variables we get different kinds of transonic solutions with drastically different topologies, but for the same set of constants of motion. In addition, there is no known principle dictated by plasma physics which may constrain the relation between these two-temperatures in any of the boundaries. We removed the degeneracy with the help of second-law of thermodynamics. We show that only one of the solutions among all, has the maximum entropy and therefore is the correct solution, thus eliminating degeneracy. As far as we know no methodology of obtaining unique transonic two-temperature solutions has been reported so far in literature. This is the first time we have attempted towards obtaining the general-picture of the physical solutions.

Dr.	Ritabrata		Biswas	The University of Burdwan	Title : Threshold Drop in Viscous Dark Energy Accretion Density\n\nAbstract : Recent researches of galactic cores tell us that supermassive black holes are residing at each of them. We got several evidence even. Besides, dark matter halo is expected to be distributed all over in our universe. Galactic structures are supposed to be formed out of dark matter clustering. Some examples of supermassive black holes in the central regions of high redshift galaxies say that supermassive black holes have completed their construction in a time less than it generally should be. To justify such discrepancies, we are forced to model existences of black hole mimickers and exotic phenomena acting near the supermassive black holes. We are motivated by this to study the nature of exotic matters, especially dark energy near the black holes. We choose modified Chaplygin gas as dark energy candidate. Again form the description of gravitational wave or the attenuation of it when it is tunnelling through cosmological distances helps us to measure the shear viscosity of the said medium. Delayed decaying models of dark matters also suggest that dark energy and viscosity may come up as a byproduct of such decay or interactions. We consider viscous nature of the medium, i.e., the dark energy. To do so, we choose alpha-disc model as proposed by Shakura and Sunyaev. We study the variations of densities through accretion and wind branches for different amount of viscosity regulated by the alpha parameter, spin parameter and different kind of accreting fluids, viz, adiabatic fluid and modified Chaplygin gas. We compare these results with each other and some existing density profiles drawn from observational data based simulations. We follow our result to support data observed till date. Specifically, we see the wind to get stronger for dark energy as accreting agent and accretion to have a threshold drop if viscosity is taken along with the repulsive effects of dark energy.

Prof.	SARMISTHA		BASU	Behala College, Kolkata, West Bengal, India	Gravitational waves are a prediction of the early universe Abstract: The gravitational waves originated from a pair of merging black holes. The gravitational wave background is a random gravitational wave signal produced by a large number of weak, independent, and unresolved sources. It is a possible target of gravitational wave detection experiments. The observational astronomy uses gravitational waves to collect observational data about sources of detectable gravitational waves such as binary star systems composed of white dwarfs, neutron stars, and black holes; and events such as supernovae, and the formation of the early universe shortly after the Big Bang. Observers detecting this radiation today are able to see the Universe at a very early stage on what is known as the `surface of last scattering'. Photons in the cosmic microwave background have been travelling towards us for over ten billion years, and have covered a distance of about a million billion billion miles. The cosmic microwave background radiation, corresponding to radiation from a blackbody at a temperature of nearly 3 K, is the greatly redshifted remnant of the hot universe as it existed about 380,000 years after the Big Bang. During the first 380,000 years of the universe, radiation and matter formed an opaque plasma called the primordial fireball. The detection of such a background would have a profound impact on early- universe cosmology and on high-energy physics. Keywords: white dwarfs, neutron stars, supernovae, redshifted

Mr.	Shailesh		Kumar	Indian Institute of Information Technology Allahabad	Title : BMS like symmetries for Impulsive Gravitational Waves ; \n\nAbstract:\n\nBlack holes are arguably one of the most intriguing objects in nature that has offered many outstanding phenomena. One of the interesting aspects of black hole spacetime is to see how spacetime symmetries affect the near and far region physics of black holes. Recently it has been shown that BMS-like symmetries appear as soldering freedom when we glue two spacetimes along a null surface. Gluing of two spacetimes across a null surface also produces impulsive gravitational waves (IGWs) having a Dirac delta function type pulse profile along the surface. This kind of shock waves are usually produced in astrophysical phenomena. I will discuss some measurable effects of such shock waves (IGWs) on test particles. It is found that these IGWs leave footprints that depend on BMS-like symmetry parameters upon passing through the test particles. This is reminiscent of the gravitational memory effect originally discovered in far region.

Mr.	Pradeepkumar	Ramrathi	Yadav	Birla Institute of Technology and Science, Pilani	Majority of LMXBs have been observed to be rotating in a narrow frequency range with a time period in the millisecond range. A few attempts have been made to understand such interesting behaviors, namely existence of upper cut-off frequency in accreting neutron stars of these X-ray binaries, which include coupling of NS magnetosphere with the accretion disk, gravitational radiation, etc. There was a proposal that asymmetric electron capture by an accreting NS can produce\nquadrupole moment (QM) which in turn can generate gravitational waves (GWs) to compensate the spin up caused by adding angular momentum due to accretion. In this talk, we shall discuss the role of pre-existing QM of an accreting NS as a natural explanation for such behavior. We assume the existence of triaxiality (i.e., ellipticity) of a NS. The magnitude of ellipticity can be set from the requirement of the maximum strain a NS can sustain against stress due to elastic deformation. We have shown that the value of triaxiality and hence the quadrupole moment we obtain from the above criteria can be sufficient to maintain the torque balance by the accreting stars. Our proposal seems to provide a natural explanation toward the existence of upper cut off frequency\namong the LMXBs.

Dr.	Nagendra		Kumar	Postdoctoral Fellow, Department of Physics, IISc, Bangalore	Title : A continuous-jet Leptonic model for Blazars SED â€“ its application to GRBs\n\nAbstract:\nBlazars (FSRQs and BL Lacs objects) are the radio loud and gamma-ray bright active galactic nuclei (AGNs) with a highly collimated relativistic jet of plasma aligned at close angles to our line of sight. The broadband spectral enrgy distributions (SEDs) of blazars show two hump (in vF_v plot): a low-energetic hump extends radio to optical/ X-rays, generated by synchrotron process inside the jet, and a high-energetic hump extends X-rays to gamma-ray, generated by inverse Compton IC process in Leptonic model. Depending on seed-photon source, IC process is subdivided into synchrotron self Compton (SSC) and external Compton (EC, here seed photons are other than synchrotron photon). FSRQs and low synchrotron peak (LSP) BL Lacs exhibit a Compton dominance (CD, the ratio of luminosities at gamma-ray peak to synchrotron peak) SEDs, i.e., CD >1. Further, the radio to gamma-ray emission is Doppler boosted, e.g. in One-zone model.\nRadio imaging of blazars show a powerful, highly collimated relativistic jet. Motivated by this, we studied the broadband SED in a steady continuous conical jet, primarily an anisotropic relativistic flow along the jet axis. For anisotropic flow, we considered two velocity components for electrons, one along the jet axis in conically forward direction while the other is a random component perpendicular to the jet axis where the average random speed is less than average forward speed electrons. We calculated the broadband SED using synchrotron and IC processes assuming a cylindrical (of radius R and length L) emission region inside the jet. Here, in IC process photons will get upscattered by both components of electron velocity, and to compute the IC spectrum we used a Monte Carlo approach.\nWe found, in a steady continuous conical jet assuming leptonic emission scenario and anisotropic flow in helical magnetic field with broken power-law electrons distribution, one can modeled the blazars SED successfully as well as general short and high amplitude variability; the radiation is beamed, but not by bulk Doppler boosting, and is unaffected from the pair-production. Our formalism and set-up also allow to investigate the effect of the geometry and dimension of emission region on observed broadband spectra. We found that the SEDs of LSP blazars (CD >1) can be explained by considering SSC only with a low value of R/L (< 0.01). Our model has degeneracy between non-thermal electron number density (n_e) and length of the emission region (L) which allow us to reproduce any variability (even order of 1s) in terms of particle density. Example: The SED of CD =10 can be modeled by (synchrotron + SSC) only with R/L=0.0001 in single scattering limit and 1s gamma-ray variability would be explained with n_e = 10^{22} cm^{-3}. Our model is able to explain, the SEDs of CD >1 in SSC process, and any short variability. It can be a plausible radiation mechanism for GRBs SED which is further supported by theirs polarization studies.

Ms.	Unnati		Kashyap	Indian Institute of Technology Indore	Compact objects in binary systems exhibit the most extreme strong field gravity effects as the gravitational curvature and potential nearby jointly reaches maximally high values. Theories of gravity can be tested by comparing the predictions and the observational signatures present in the surrounding, specifically in the accretion disk. The emission from the accretion disk is mainly in the X-ray band and can be of very high luminosities associated with a strongly variable nature. Understanding the accretion mechanism and the evolution during various phases of the active state can shed light on the gravitational effects on the compact object. We report the analysis of broadband AstroSat observations of the poorly studied accreting neutron star Low Mass X-ray binary 4U 1724-30 in 2017 which corresponded to the low-luminosity non-thermally dominated state of the source. All of the X-ray broadband spectra can be modeled by blackbody radiation plus power law (possibly suggesting non-thermal Comptonization). The timing variabilites were also investigated to probe the origin of disk and coronal fluctuations and their dependence on mass accretion. The spectro-temporal analysis and time lag properties of the broadband emission was carried out to uniquely derive information about the complete radiative emission behavior and its evolution. This unprecedented broadband study will be instrumental to understand the nature of physical processes occurring in the accretion flow as well as corona.

Mr.	Amitesh		Singh	Department of Mechanical Engineering,National institute of Technology,Surat, Gujarat, India-395007	Gravitational waves are produced by collision of black holes, by the event of supernovae, coalescing neutron stars, also due to asymmetric and wobbly rotation of neutron stars. Omicron-LIB (oLIB), coherent wave burst (cBW), and Bayes Wave follow up are the algorithms which filter the gravitational wave strain data from the noise and glitches. The data is taken from LIGO GWOSC. Bayes Wave algorithm is used to obtain the training data set for our Machine Learning model. We input the training set to the Machine Learning Model which characterizes the GW data and finds the type of source (Binary Black hole mergers , Binary Neutron star mergers, Supernova remnant, Gamma ray bursts).

Mr.	Koustav		Chandra	IIT Bombay	Probing extra modes of gravitational wave polarisation modes using gravitational wave observations\nKoustav Chandra, Archana Pai\n\nAbstract \nThe detection of gravitational waves has provided us with an opportunity to test general relativity in the strong field regime. In the absence of detailed calculations of waveforms from modified theories of gravity, most tests performed so far are consistency test. In this paper, we discuss the possibility of using the network of ground based interferometer to directly measure extra modes of polarisation of gravitational waves in a model-independent way using transient signals from astrophysical sources. We use the fact that for sources observed with at least three detectors, it is in principle possible to distinguish the different polarisation modes owing to detectorsâ€™ different antenna pattern for different polarisations.

Mr.	Avijit		Chowdhury	Indian Institute of Science Education and Research Kolkata	Title: A study of the quasi normal modes of a charged spherical black hole with scalar hair and its superradiant stability.\n\nAbstract: In this work we study the quasinormal modes of charged and uncharged massive scalar fields and also of charged Dirac fields against the background of a charged spherical black hole endowed with a scalar hair. Special emphasis has been given to the case where negative scalar charge dominates over the electric charge of the black hole which mimics an Einstein-Rosen bridge. Except for the complete monotonic behaviour of the damping (imaginary part of the quasinormal frequency) against the charge of the black hole as opposed to the existence of a peak for the pure Reissner- NordstrÃ¶m case, the qualitative behaviour does not appreciably change due to the presence of scalar hair. The system also appears to be stable against superradiance irrespective of the mass of the test scalar field.

Ms.	SUCHETA		DATTA	St.Xavier	In this paper, we have considered a toy model of an anisotropic universe and studied the propagation of gravitational waves in such a universe. The consideration of this toy model simplifies the analysis and helps us to illustrate the effects of anisotropy. Incorporating linear perturbations on this anisotropic background, we have considered the synchronous, transverse, traceless gauge conditions and evaluated the perturbations of the Ricci tensor. The energy-momentum tensor is that of a perfect fluid, for which the Einstein's field equations are determined in presence of perturbations. We arrive at the set of linearized Einstein's equations explicitly and find solutions for gravitational waves propagating along the direction of anisotropy. We also study the propagation along a direction perpendicular to the direction of anisotropy. Subsequently we have validated the assumption of the tracelessness of the linear perturbations. Finally we determine the amount of tidal acceleration caused by the propagation of gravitational waves in this background spacetime. [ arXiv:1908.06743 ]

Ms.	Sangita		Chatterjee	Jadavpur University	Title: Gravitational-wave emission from a binary merger.\nAbstract: Supermassive black holes in our galactic centers are likely to contain large massive accretion disk. This disk may exert a non-negligible hydrodynamic drag on the compact objects rotating around the central black hole. Hence, the gravitational wave signal emitted from an extreme and intermediate-mass ratio inspirals may be modified due to the modified motion of orbiting companion by the influence of hydrodynamic drag of the disk. In the present work, we investigate this issue using full general relativistic formalism. We wish to estimate precisely the change of the amplitude and frequency of the gravity wave signal due to the effect of the accretion disk and find out the possible error introduced in the estimation of the mass of the central black hole.

Dr.	Oindrila		Ganguly	Physical Research Laboratory, Ahmedabad	We extend the study of dynamical black holes to the domain of analogue models of gravity for reasons of theoretical curiosity and observational advantages. \nIn a general analogue model, we construct a dynamical acoustic black hole spacetime with longitudinal symmetry. We identify its degenerate evolving horizon and marginally outer trapped surface, calculate a dynamical surface gravity for the same using the inaffinity property of outgoing longitudinal null geodesics and argue that this should be related to the temperature of thermal Hawking radiation emitted from the horizon. Experimental realisation of our proposed non-stationary acoustic spacetime and observation of Hawking radiation from a local horizon can lend invaluable insight into the study of physical dynamical spacetimes in general relativity.

Mr.	Dhruba	Jyoti	Gogoi	Dibrugarh University	Title: Polarization Modes of Gravitational Waves in Hu Sawicki Model and Rastall Gravity\n\nAbstract: Detection of Gravitational Waves (GWs) by LIGO and VIRGO collaborations has opened a new way to test Extended Theories of Gravity (ETGs). Recent events GW170814 and GW170817 have ruled out some ETGs and put a very strong constraint on General Theory of Relativity and other remaining/surviving ETGs. In this study, we have selected two of such surviving ETGs. We have checked the polarization modes of GWs in Hu Sawicki model of f(R) gravity and Rastall theory of gravity from the properties of geodesic deviation and using Newmann Penrose formalism. The Hu Sawicki model has been studied under the metric formalism. The study shows that the polarization characteristics of GWs in f(R) gravity are different from those obtained in Rastall gravity. In Hu Sawicki model of f(R) gravity, four polarization modes of GWs viz., tensor plus, tensor cross, breathing and longitudinal modes of polarization are obtained. Whereas in Rastall theory of gravity, no massive mode of polarization is found. The study in principle can help to discriminate between these two ETGs.

Ms.	JYATSNASREE		BORA	DIBRUGARH UNIVERSITY	Title: Comparison of radial oscillation frequencies of strange star for\nvarious Equation of States (EOSs)\n\nAbstract: We study the properties of radial oscillations of a special type of compact star i.e. of strange star for three different EOSs viz., MIT Bag model EOS, polytropic EOS and linear EOS. For the MIT Bag model we used the bag constants B = (148M eV ) 4 , for the polytropic EOS, the polytropic index (1 + 1/n) is taken as 1.5 and for linear EOS, the linear constant n is taken as 0.463. The Tolman-Oppenheimer-Volkoff (TOV) equations for strange stars are solved numerically to get eigenfrequencies of the star for each modelâ€™s\nEOS. For each EOS we found 22 lowest radial eigenfrequency modes, which show a sharp model dependency. The comparison of the results for these EOSs show that polytropic EOS has the lower value of fundamental f -mode and pressure p-mode than that of MIT Bag model and linear EOSs. Whereas linear EOS shows larger oscillation frequencies.

Mr.	Dhruba	Jyoti	Gogoi	Dibrugarh University	Title: Polarization Modes of Gravitational Waves in Hu Sawicki Model and Rastall Gravity\n\nAbstract: Detection of Gravitational Waves (GWs) by LIGO and VIRGO collaborations has opened a new way to test Extended Theories of Gravity (ETGs). Recent events GW170814 and GW170817 have ruled out some ETGs and put a very strong constraint on General Theory of Relativity and other remaining/surviving ETGs. In this study, we have selected two of such surviving ETGs. We have checked the polarization modes of GWs in Hu Sawicki model of f(R) gravity and Rastall theory of gravity from the properties of geodesic deviation and using Newmann Penrose formalism. The Hu Sawicki model has been studied under the metric formalism. The study shows that the polarization characteristics of GWs in f(R) gravity are different from those obtained in Rastall gravity. In Hu Sawicki model of f(R) gravity, four polarization modes of GWs viz., tensor plus, tensor cross, breathing and longitudinal modes of polarization are obtained. Whereas in Rastall theory of gravity, no massive mode of polarization is found. The study in principle can help to discriminate between these two ETGs.

Mr.	Akash		Garg	Department of Physics, Jamia Millia Islamia	Modeling the temporal behavior of Blackhole X-ray binary G RS 1915+105" - Several Galactic Black hole binaries possess variability such as Quasi-periodic oscillations(QPOs) in X-ray luminosity. The radiative components which produce such QPO phenomena can be understood from their energy and frequency-dependent temporal behavior. In order to do that one has to determine the correlations that exist between the energy-dependent fractional r.m.s. and time lags and variations in time-averaged spectral parameters. However, the spectral parameters so obtained needs to be further recasted into physical ones to develop a better understanding of accretion geometry. In this work, we are developing a model where oscillations in physical parameters associated with the underlying radiation processes can produce seen qualitative temporal variability in the binaries. As an example, we are using observation of 竏ｼ 3-4 Hz QPOs in GRS 1915+105, observed by ASTROSAT/LAXPC in the wide energy band of 3.0-80.0 KeV. Its time-averaged spectrum can be modeled by thermal Comptonized emission from hot coronae near the Black hole along with blackbody emission from the outer truncated disk. We �ｬ］d that the time-delays between the response of variations in coronal heating rate, truncated disk radius and inner disk temperature can reproduce the energy-dependent behavior of QPOs and their harmonics

Dr.	ALOKE	KUMAR	SARKAR	CMPRC, Phys. Dept., Jadavpur University, Kolkata 700032	A Phenomenological Study on Diffraction of Gravity Wave by Mass Cluster\n\nA.K. Sarkar\n\nGravity Wave(GW) is the propagation of ripples in spacetime curvature on scales smaller than characteristics scales of background spacetime. Following prediction of general theory of relativity that moving bodies may emit GW whose frequencies are dependent on orbital parameters . GW diffraction by star clusters has gained tremendous impact on cosmological studies. In this phenomenological study GW emitted by massive or super massive body near galactic centre considered as source and star cluster between source and observation centre as diffracting object. In this simple preliminary study finite cluster is considered like 3-D crystalline lattice with stars as lattice points. The overall parameters are considered consistent with appropriate diffraction effect.This over simplified analysis ignored shear distortion of source and diffracting object. Correction due to dynamics within the cluster over the results from static cluster is also attempted. The overall results obtained are compared and found to be encouraging.

Ms.	Sandhya		Jagannathan	University of Delhi	Magnetic fields are present on galaxy cluster scales as indicated by Faraday rotation observations. These fields can play a major role in the dynamics of galaxy clusters. We study their effect on the estimation of gas mass through the modification of the hydrostatic equilibrium condition and further study its impact on the gas mass fraction. We also study its impact on unrelaxed and relaxed galaxy clusters separately. For our analysis, we have used predetermined number density and temperature profiles of 35 galaxy clusters consisting of 22 unrelaxed and 13 relaxed clusters. We also employ the Navarro, Frenck and White profile (NFW) to determine the total mass. We infer from our analysis, that for X-ray determined total masses, the magnetic field effect at r500 is less than 1 % whereas for NFW determined total masses, the effect of the magnetic field increases slightly to be closer to 1 %. On the whole, we conclude from our analysis that the effect of magnetic field on the gas mass fraction of galaxy clusters can be neglected. This being especially true for relaxed clusters.

Prof.	SARBARI		GUHA	Department of Physics, St. Xavier	In this paper we have examined the validity of a proposed definition of gravitational entropy in the context of accelerating black hole solutions of the Einstein field equations, which represent the realistic black hole solutions. We have adopted a phenomenological approach proposed in Rudjord et al [20] and expanded by Romero et al [21], in which the Weyl curvature hypothesis is tested against the expressions for the gravitational entropy. Considering the C-metric for the accelerating black holes, we have evaluated the gravitational entropy and the corresponding entropy density for four different types of black holes, namely, non-rotating black hole, non-rotating charged black hole, rotating black hole and rotating charged black hole. We end up by discussing the merits of such an analysis and the possible reason of failure in the particular case of rotating charged black hole and comment on the possible resolution of the problem. [arXiv:1908.06763v1]

Mr.	Shashwat		Singh	Department of Mechanical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat	The Gravitational Waves (GW) are the traversing solution of General relativity. These waves originate from different astrophysical bodies that perturb the space-time. Such perturbations are observed and recorded by the LIGO-VIRGO setup that generates signals corresponding to the same. These signals usually are mixed with the noise that affects the transient change in the GW signal through which any astrophysical event could be predicted. We have used a deep learning method with two deep convolutional neural networks mentioned as Deep Filtering Method used for end-to-end time-series signal processing. It is designed for classification specifically the detection of GW signals in noisy time-series data streams collected by the LIGO-VIRGO setup. The results are further tested for the astrophysical events using an Artificial Neural Network (ANN) that will collect the transient Gravitational-Wave signal as the input from the previous Deep Filtering Method and predict the properties of the astrophysical event. The same predictions are to be used to cluster the event and their corresponding Gravitational-wave signature. The data used for training the model include O2 16 KHz (detectors placed at Hanford, Livingston and Louisiana beginning from 2016-11-30 16:00:00 to 2017-08-25 22:00:00) and O1 16KHz (detectors placed at Hanford, Livingston beginning from 2015-09-12 00:00:00 to 2016-01-19 16:00:00) and for testing datasets includes all the so far discovered Gravitational-Wave signatures. The results obtained have good accuracy in predicting the properties of the astrophysical event of their respective Gravitational-wave signature.

Mr.	HIMANSHU		SWAMI	IISER, MOHALI	BREAKING NEUTRINO MASS HIERARCHY USING GRAVITATIONAL INDUCED FLAVOR OSCILLATIONS: \n\nWe study gravitational interference effect in neutrino flavor in the background of Schwarzschild geometry. For this purpose, we employ weak lensing in Schwarzschild background for two neutrino flavour case. It is observed that for certain trajectories, flavor transition probability has a sensitivity on absolute masses of neutrinos rather than just \mass square difference\". This is in contrast to neutrino oscillation in flat spacetime. We discuss feasibility of this result in probing the absolute masses of neutrinos in lensing experiments. In particular we estimate the time scale for observing the mass dependent oscillations considering the Sun as a gravitational source."

Ms.	PARVEEN		BANO	SAMBALPUR UNIVERSITY	Intensity of Gravitational wave emitted from r-mode instability of Neutron Star :-\n\n\nThe r-mode oscillations are the surface current on the Pulsar Neutron star (NS) to which the Coriolis force provides the real dynamics [1, 2], as a result of which the Pulsar become a continuous source of Gravitational waves (GW) by the Chandrasekhar-Friedman-Schutz (CFS) mechanism. The instability due to the continuous emission of GWs is counterbalanced by the viscous effects of the NS core. However, the angular velocity Ï‰ of the r-mode is a function of angular velocity of the NS â„¦ and temperature T. If â„¦ of the NS exceeds a critical value â„¦c(T), then the r-mode become unstable as the viscous mechanism could no more counterbalance the instability due to emission of GWs. Thereby the amplitude of the r-mode, Î±, go on increasing till it attains a saturation value. At this point the Pulsar NS emits a massive GW emitting itâ€™s energy and angular momentum and spin-down to the region of stability. The intensity of the GW emitted is calculated for 1.4 and 1.8 Mâ—‹ NS models and it has been found that the lateral strain exerted by these GWs lie below the range of the LIGO. The future improvements in LIGO can provide information on these GWs emitted under r-mode instability and hence can give meaningful information on many elusive aspects of equation of state (EOS) of isospin asymmetric dense matter [3]. The EOS used in the study of GW from r-mode instability has been checked with the deformability Î› data extracted from the last detected event of two neutron star merger GW170817 [4, 5, 6], and the predicted Î› of the EOS lies within the range extracted from the data of the event by LIGO-Virgo collaboration.\n\nReferences :\n[1] Andersson N 1998, Astrophys. J 502 708.\n[2] Lindblom L, Owen B J and Morsink S M 1998, Phys. Rev. Lett. 80 4843.\n[3]S P Pattnaik, T R Routray, X ViÃ±as, D N Basu, M Centelles, K Madhuri and B Behera, J. Phys. G: Nucl. Part. Phys. 45 (2018) 055202.\n[4] Abbott B P et al (Virgo, LIGO Scientific) 2017 Phys. Rev. Lett. 119 161101.\n[5] Abbott B P et al (Virgo, LIGO Scientific) 2017 Astrophys. J 848 L12.\n[6] Abbott B P et al (Virgo, LIGO Scientific) 2018 Phys. Rev. Lett. 121 161101.

Mr.	Prasanna	Mohan	Joshi	Indian Institute of Science, Education and Research(IISER), Pune.	The LIGO and VIRGO Detectors have conducted two observation runs, in which a total of ten binary black-hole mergers and neutron star mergers have been detected. The next observation run is expected to detect many more sources. Search algorithms involve cross-correlation of data from detectors with a template and searching with a template bank in parameter space. This method works very well, if noise in the detector data is Gaussian and stationary. That is actually not the case. The data is extremely noisy and contains a lot of glitches. These glitches produce false \ntriggers which need to be identified and weeded out.\nIn this project, we will be exploring vetoing techniques which differentiate between triggers due to glitches and due to signal. Several of these glitches are viable to modeling in which case optimal vetoing techniques can be designed. We will explore such optimal techniques theoretically and also with simulated and real data.

Mr.	Anshu		Gupta	Consultant, Gravitational Wave Physics Group, IUCAA, Pune	Title: Orbital merger of binary black holes surrounded by scalar field cloud. Abs: In general relativity, non-existence of mass-less scalar fields in a static, spherically symmetric, asymptotically flat space-time has been known for a long time. However, multiple studies have shown that relaxing the static condition could lead to scalar field configurations in quasi-bound states on non-static backgrounds. Among those are, configurations of massive scalar fields surrounding a black hole [1]. These configurations could be classified somewhere between boson stars and black hole systems which are among the potential candidates of 'black hole mimickers'. Quasi-stationary solutions of such self-gravitating scalar fields around black holes[2], collapsing stars and accreting black holes have been studied in the last few years. In the current work, focus is on the orbital merger of binary black holes surrounded by scalar field cloud. While numerically evolving such configurations, we notice the difference in waveforms as compared to the binary black hole mergers in absence of scalar fields around it. We find larger deviation in the waveforms for scalar field with the larger mass $\mu$ and higher field strength $\phi_0$. Its impact on the gravitational wave signals detected through ground based and space based detectors due to such sources would be discussed.
Mr.	Abdul		Quddus	Department of Physics, Aligarh Muslim University	We have studied the properties of a neutron star (NS) in the presence of weakly interacting massive particles (WIMPs) dark matter. The dark matter (DM) is considered inside the core of a neutron star, which softens equations of states (EOSs) of NS. Consequently, the properties of NS such as mass-radius relation, tidal deformability, and moment of inertia decrease. The studied properties are compared with the GW170817 data. We have also studied the universality relations to constrain the parameters of DM Lagrangian density. In this study, we have used recently generated IOPB-I, FSUGarnet, and NL3 parameter sets within relativistic mean-field formalism to predict EOS of NS in the presence of DM.	Shifted to Workshop 1