AR_final file_2018-19

and galactic absorption. We have also probed the relation between the spectral and temporal param- eters. It is found that the fractional rms ampli- tude anti-correlates the QPO centroid frequency, whereas disk inner radius correlates the QPO cen- troid frequency. More interestingly, it is observed from the obtained values of the disk fraction and the Comptonized fraction from the time resolved spectroscopy that the maximum amount of the to- tal flux is coming from the Comptonized photons, where the Comptonized flux in the 0.7-79 keV re- gion is always > 95%. From these results, it is con- firmed that only the Comptonized photons are re- sponsible for the variability in the system. All the above mentioned results obtained from the tempo- ral and spectral analysis well agree with the LHS state behaviour of the system during the rising phase of the 2016 outburst. This work has been done in collaboration with Swadesh Chand, Gulab C. Dewangan, and Vivek Agrawal. Sunil Kumar Tripathy Bianchi-V cosmological model with dark energy anisotropy The role of anisotropic components on the dark energy and the dynamics is investigated. An anisotropic dark energy fluid with different pres- sures along different spatial directions is assumed to incorporate the effect of anisotropy. One dimen- sional cosmic strings aligned along x-direction sup- plement some kind of anisotropy. Anisotropy in the dark energy pressure is found to evolve with cosmic expansion at least at late times. At an early phase, the anisotropic effect due to the cosmic strings sub- stantially affect the dynamics of the accelerating universe. This study has been done in collabora- tion with B. Mishra, and Pratik P. Ray. Anisotropic cosmological reconstruction in f ( R, T ) gravity Anisotropic cosmological models are constructed in f(R,T) gravity theory to investigate the dynam- ics of the universe concerning the late time cos- mic acceleration. Using a more general and simple approach, the effect of the coupling constant and anisotropy on the cosmic dynamics have been in- vestigated. It is found that cosmic anisotropy sub- stantially affects the cosmic dynamics. This study has been done in collaboration with B. Mishra, and Sankarsan Tarai. Pranjal Trivedi Magnetic heating across the cosmological recombi- nation era: Results from 3D MHD simulations The origin of cosmic magnetic fields is an unsolved problem and magnetogenesis could have occurred in the early Universe. We study the evolution of such primordial magnetic fields across the cosmo- logical recombination epoch via 3D magnetohydro- dynamic numerical simulations. We compute the effective or net heating rate of baryons due to de- caying magnetic fields, and its dependence on the magnetic field strength and spectral index. In the drag-dominated regime ( z & 1500), prior to recom- bination, we find no real heating is produced. The simulations allow us to smoothly trace a new tran- sition regime (600 . z . 1500), where magnetic energy decays, at first into the kinetic energy of baryons. A turbulent velocity field is built up un- til it saturates, as the net heating rate rises from a low value at recombination to its peak towards the end of the transition regime. This is followed by a turbulent decay regime ( z . 600), where mag- netic energy dissipates via turbulent decay of both magnetic and velocity fields, while net heating re- mains appreciable and declines slowly. Both the peak of the net heating rate and the onset of turbu- lent decay are delayed significantly beyond recom- bination, by up to 0.5 Myr (until z ≃ 600 − 700), for scale-invariant magnetic fields. We concen- trate on low magnetic field strength to avoid confu- sion with magnetic field-generated density fluctua- tions. Analytic approximations are provided and we present numerical results for a range of field strengths ( ≃ 10 − 3 − 2 × 10 − 2 nG) and spectral in- dices, illustrating the redshift-dependence of dissi- pation and net heating rates. These can be used to study cosmic microwave background constraints on primordial magnetic fields. This study has been done in collaboration with Johannes Reppin, Jens Chluba, and Robi Banerjee. Vinutha Tummala Dark energy cosmological models with cosmic string We have studied the anisotropic KantowskiSachs, locally rotationally symmetric (LRS) Bianchi type- I and LRS Bianchi type-III geometries filled with dark energy, and one dimensional cosmic string in the Saez-Ballester theory of gravitation. To get physically valid solution, we take hybrid expansion ( 217 )