AR-2019-2020

and needs to be cleaned up by deconvolution. The deconvolution procedure involves the inversion of the beam matrix which is expressed in terms of basis functions. So far in the literature, two bases have been used: (i) the pixel basis, and (ii) the spherical harmonic basis. In this project, P. Upadhyaya, Sanjeev Dhurandhar and Shivraj Kandhasamy propose to explore a third basis which is natural to the problem - namely, the point spread functions themselves. The point spread functions are intersections of the sky sphere with cones determined by the baseline joining the detectors. We expect this approach to lead to an efficient handling of the problem. Time-delay interferometry for LISA (Laser Interferometric Space An- tenna) The review article written by M. Tinto and Sanjeev Dhurandhar dated earlier of 2014 has been now updated after the discovery of gravitational waves. The update was necessary, because the design of LISA has changed in recent years for various reasons such as technological advances. The article now incorporates the changes from the current experimental design. On another front, more insights on the mathematics have been added, for example, how this work relates to the famous Hilbert’s syzygy theorem, etc. Our current experience with real data from ground-based detectors has shown why it is important to adopt an approach in which the statistical constructs from the data analysis are free from singularities. The algebraic-geometric approach described in the article is inherently singularity free. Cosmic Magnetic Fields Characterising the dynamo in a radiatively inefficient accretion flow The MRI driven dynamo in a radiatively inefficient accretion flow (RIAF) using the mean field dy- namo paradigm was explored by Prasun Dhang, Abhijit Bendre , Prateek Sharma, Kandaswamy Subramanian . Using singular value decomposition (SVD), the least squares fitting dynamo coef- ficients α and γ were obtained, by comparing the time series of the turbulent electromotive force and the mean magnetic field. This study is the first one to show the poloidal distribution of these dynamo coefficients in global accretion flow simulations. Surprisingly, a high value of the turbulent pumping coefficient γ was obtained, which transports the mean magnetic flux radially outward. This would have implications for the launching of magnetised jets which are produced efficiently in presence a large-scale poloidal magnetic field close to the compact object. A scenario of a trun- cated disc beyond the RIAF, where a large scale dynamo-generated poloidal magnetic field can aid jet-launching close to the black hole was explored. Magnitude of all the calculated coefficients decreases with radius. Meridional variations of α φφ , responsible for toroidal to poloidal field con- version, is very similar to that found in shearing box simulations using the ‘test field’ (TF) method. By estimating the relative importance of α -effect and shear, it was concluded that the MRI driven large-scale dynamo, which operates at high latitudes beyond a disc scale height, is essentially of the α − Ω type. Generation of large scale magnetic fields due to helicity and shear Coherent large-scale magnetic fields and mean differential rotation are two common features of most astrophysical objects, such as the Sun, stars, galaxies, etc. Magnetic fields in these systems are maintained by turbulent dynamo action, where the standard paradigm for large-scale component involves amplification of weak seed fields due to helical turbulence in shear flows. The alpha-effect, which in idealized settings, is a measure of net kinetic helicity and arises naturally in systems with rotation and stratification, plays a crucial role in driving large-scale dynamos in a variety of systems. In a recent work, Nishant Singh , together with Naveen Jingade, studied the mean field dynamo action in a background linear shear flow by employing pulsed renewing flows with fixed kinetic helicity and non-zero correlation time. They used plane shearing waves in terms of time-dependent