AR_final file_2018-19

and Parizath Deb Roy. Generation of sheath in magnetized plasma under the impact of slow rotation In this study, we have tried to investigate the gener- ation of sheath in magnetized plasma rotating with a uniform angular velocity about an axis making an angle with the direction of plasma acoustic wave propagation. In a marked contrast to the earlier studies, here the simultaneous impact of slow ro- tation and external magnetic field have been taken into consideration. Previous studies have revealed that the Coriolis force generated from rotation has a tendency to produce an equivalent magnetic field effect as and when the ionized medium rotates. The variations of sheath potential with normalized dis- tance for different values of angles of rotation as well as for different values of Mach number have also been investigated for typical plasma parame- ters. This work has been done in collaboration with Jaydeep Paul, and Apratim Nag. Sudipta Das A new parametrization of dark energy equation of state leading to double exponential potentia We show that a phenomenological form of energy density for the scalar field can provide the required transition from decelerated ( q > 0) to accelerated expansion ( q < 0) phase of the universe. We have used the latest type Ia supernova (SNIa) and Hub- ble parameter datasets to constrain the model pa- rameters. The best fit values obtained from those datasets are then applied to reconstruct ω φ ( z ), the equation of state parameter for the scalar field. The results show that the reconstructed forms of q ( z ) and ω φ ( z ) do not differ much from the standard ΛCDM value at the current epoch. Finally, the functional form of the relevant potential V ( φ ) is derived by a parametric reconstruction. The corre- sponding V ( φ ) comes out to be a double exponen- tial potential, which has a number of cosmological implications. Additionally, we have also studied the effect of this particular scalar field dark en- ergy sector on the evolution of matter overdensi- ties. This work has been done in collaboration with Abdulla Al Mamon, and Manisha Banerjee. Abhirup Datta The galaxy cluster pipeline for X-ray temperature maps: ClusterPyXT ClusterPyXT is a new software pipeline to gen- erate spectral temperature, X-ray surface bright- ness, pressure, and density maps from X-ray ob- servations of galaxy clusters. These data products help to elucidate the physics of processes occur- ring within clusters of galaxies, including turbu- lence, shock fronts, non-thermal phenomena, and the overall dynamics of cluster mergers. Cluster- PyXT automates the creation of these data prod- ucts with minimal user interaction, and allows for rapid analyses of archival data with user defined parameters and the ability to straightforwardly in- corporate additional observations. In this work, we describe in detail the use of this code and release it as an open source Python project on GitHub. This work has been done in collaboration with B. Alden, E. J. Hallmann, D. Rapetti, and J. O. Burns. Study of diffuse emission in cluster MACSJ0417.5- 1154 from 76 MHz to 18 GH We present new radio observations of the mas- sive and X-ray luminous galaxy cluster MACS J0417.51154, at 1.387 GHz and 18 GHz, from the Giant Metrewave Radio Telescope (GMRT) and the Australia Telescope Compact Array (ATCA) respectively. We estimate diffuse emission in the central region of the cluster at 1.387 GHz and 18 GHz. We combine these data with previously pub- lished results and present the spectrum of diffuse emission from 76 MHz to 18 GHz. This is possibly a unique study of the radio halo emission in galaxy cluster over this wide range of frequencies. Such studies lay the prospects of future studies with ra- dio telescopes with wide-range of frequencies like the Square Kilometre Array (SKA). Our 1.387 GHz data, with 2 ′′ angular resolution, provides a better estimate of point source emission than previous L- band observations, which is crucial, given the claim of sharp steepening of the radio halo spectrum at 0.61 GHz reported earlier. We find that the spec- trum of the radio halo has a spectral index fit up to 18 GHz, and yields a spectral index between 76 MHz and 18 GHz that fits the available data better than earlier L-band observations. We discuss possi- ble reasons for the peculiar spectral characteristics of the diffuse emission. This work has been done in collaboration with Pritpal Sandhu, Ramij Raja, ( 184 )