AR_final file_2018-19

viz., the perihelion precession of the planet Mer- cury and the deflection of light by the Sun. In connection to mathematical analysis, we consider static and spherically symmetric dyon black hole, which carries both the electric and magnetic charge simultaneously, which are encoded it by the param- eters λ 0 and β 0 . We constrain these two parameters using the solar system tests and obtain the permis- sible range from theoretical analysis based on our model, and later on compare them with the avail- able observational data. This study has been done in collaboration with Sabiruddin Molla, Amna Ali, and Saibal Ray. Shantanu Rastogi Radiative transfer modelling of atmospheric CH4 for satellite measurements in the 1.66 µ m spectral window Atmospheric methane is the second most important greenhouse gas after carbon dioxide and has signif- icant impact on the atmosphere and climate. Con- tinuous estimation and prediction of atmospheric CH4 concentrations is important for understand- ing the associated global climate change. To con- strain suitable spectral window and detector res- olutions for satellite instruments, spectral simula- tions have been performed considering tropical at- mospheric conditions. The study is focused on the 1.66 micron spectral region having CH4 bands that are suitable for its detection and estimation. Both CH4 concentration and spectral resolution are var- ied to identify optimum spectral resolution limit. The R branch peak at 1.6456 ∼ µ m is found to be the most sensitive and suitable for CH4 estimation. A concentration retrieval scheme is proposed, and it is interpreted that the spectral resolution should not be worse than 0.2 nm. This study has been done in collaboration with P. Prasad, and R. P. Singh. C.D. Ravikumar Establishing the spectral turnover of blazar PKS 2155-304 as an outcome of radiative losses Synchrotron emission from high energy electrons following a broken power-law distribution is usu- ally held responsible for the observed broad-band optical/UV and X-ray spectra of blazars. How- ever, one of the long outstanding problems has been that the observed spectral index change is signif- icantly different from the expected 0.5. Recent, high-quality observations of blazars suggest that their local spectra may not be a power law, but may contain a slight curvature that can be repre- sented by a log-parabola model. We study XMM- Newton observations spanning over 12 yr for the BL Lac PKS 2155-304, and show that the opti- cal/UV and X-ray spectra can be well represented by a broken log-parabola model. Further, such a spectrum can indicate the energy dependence of the electron escape time-scale from the main accelera- tion zone. This novel approach, besides addressing the observed difference in the photon spectral in- dices, also attempts to explain the spectral turn over in far-UV/soft X-rays as a result of the radia- tive losses. This study has been done in collabo- ration with Sitha K. Jagan, Sunder Sahayanthan, Ranjeev Misra, and K. Jena. Search for anomalous alignments of structures in Planck data using Minkowski Tensors Minkowski Tensors are tensorial generalizations of the scalar Minkowski Functionals designed to con- tain additional information of structures, like shape and alignment. We calculate Minkowski Tensors using temperature data from the Planck satel- lite, directly on the sphere and compute the net alignment in the data, extending the definition of Minkowski Tensors to random fields on curved spaces. This novel method circumvents numerical errors that can be introduced by the stereographic projection. We compare the resulting net align- ment parameter values obtained from the frequency coadded CMB temperature data, to those obtained from ΛCDM simulations of the CMB temperature sky with instrumental beam effects and residual foreground and noise. The results show very good agreement between the two within ≈ 1 σ . We fur- ther compare the alignments obtained from the beam-convolved CMB maps at individual Planck frequencies to those in the corresponding simula- tions. There is significant difference between ob- served data and simulations across all Planck fre- quencies, except for the 30 GHz channel. For the 30 GHz channel, we find ≈ 2 σ difference between the data and the simulations, which could originate from inaccuracies involved in the estimation of the instrumental beam at 30 GHz. This study has been done in collaboration with P. K. Joby, Pravabati. ( 209 )