AR_final file_2018-19

shadow is affected due to charge as well as spin. The shadow is a dark zone covered by a deformed circle, and the size of the shadow decreases with an increase in the charge q when compared with the five-dimensional Myers-Perry black hole. Interest- ingly, the distortion increases with charge q . The effect of these parameters on the shape and size of naked singularity shadow of five- dimensional EMCS black hole is also discussed. This work has been done in collaboration with Muhammed Amir, and Balendra Pratap Singh. Tuhin Ghosh Non-Gaussianity study of diffuse Galactic emission at 408 MHz The redshifted 21 cm signal from epoch of reion- ization gets contaminated by diffuse Galactic emis- sion, especially by the synchrotron emission. We use 408 MHz map and studied if there exists a clean sky region where the Galactic synchrotron emis- sion can be approximated by a Gaussian random field. Most of the existing component separation methods assume foreground emission to be Gaus- sian. We apply two statistical tools-binned bispec- trum estimator and Minkowski functional to show that the assessment of foreground emission being Gaussian is valid only at low brightness tempera- ture T < 25 K and at angular scales of 3 degrees or less. For high brightness regions ( T > 25 K ), non-Gaussianity of foreground emission needs to be taken into account in the component separation methods. This work has been done in collabora- tion with Sandeep Rana, J. S. Bagla, and Pravabati Chingangbam. Testing statistical isotropy of the Planck CMB map using Minkowski Tensors Minkowski Tensors (MTs) are recently used to study the statistical isotropy of temperature fluc- tuations of the Cosmic Microwave Background Ra- diation (CMBR). Minkowski Tensors are tensorial generalizations of the scaler Minkowski Function- als. Due to its tensorial nature they contain addi- tional morphological information of structures, in particular about shape and alignment. We have calculated MFs directly on the sphere and com- pute the net alignment of the structures seen in the Planck CMB data. We do not find any significant deviation between the data and statistical isotropic CMB simulations. We further check the alignments obtained from the beam-convolved CMB maps at individual Planck frequencies to those in the corre- sponding Planck end-to-end simulations. We find no significant departure between the data and the simulations across all Planck frequencies, except for mild 2 σ departure in the 30 GHz channel. We sus- pect that the mild departure could originates from inaccurate estimation of the instrumental beam at 30 GHz in the Planck end-to-end simulations. Rupjyoti Gogoi Modelling the mid-infrared polarization in dust around young stars The presence of crystalline silicates has been de- tected in the circumstellar environment of several young stars in the recent past, and there is evidence of silicon carbide (SiC) detection in the envelope of pre-main sequence star SVS13. In this work, we have attempted to probe the presence of SiC in the dust around protoplanetary discs in a sample of young stars. We have modelled the linear polariza- tion of composite dust grains in the mid-infrared (MIR: 8 to 13 µ m) using silicates as the host with various inclusions of SiC and graphites using the Discrete Dipole Approximation (DDA) and the Ef- fective Medium Approximation (EMA) T-Matrix methods. We have then compared our modelling results with polarimetric observations made in the protoplanetary discs surrounding two Herbig Be stars and one T-Tauri star with particular empha- sis towards the 10 µ m silicate feature using Canari- Cam mounted over the Gran Telescopio Canarias (GTC). We report the possible existence of SiC in the outer disc/envelope around one star in our sam- ple, which has been interpreted based on the shape, size, composition, and fraction of inclusions by vol- ume in our dust grain models. This work has been done in collaboration with Gautam Saikia, Ranjan Gupta, and Deepak B. Vaidya. Influence of energy-dependent particle diffusion on the X-ray spectral curvature of MKN 421 The X-ray spectral curvature of blazars is tradition- ally explained by an empirical log-parabola func- tion characterized by three parameters, namely the flux, curvature, and spectral index at a given en- ergy. Since their exact relationship with the un- derlying physical quantities is unclear, interpreting the physical scenario of the source through these parameters is difficult. To attain an insight on ( 191 )