AR_final file_2018-19

ing water source. This study has been done in col- laboration with Shashank Shekhar, S. V. N. Rao, Suman Kumar, and Diwan Singh. Magnetar signature the U curve This work looks at some definitive signatures of magnetars, in particular, of period closures ac- companied by a decline of X-ray radiation in two models. We review some of the previous works which are based on the well-known dynamo model in which the star is born with a period of a few milliseconds at high temperatures. In such a con- vection regime, the dynamo mechanism can am- plify the magnetic fields to the magnetar value. This is in contrast to a screened core model which posits that a high-density phase transition occurs in the inner core of magnetars that dynamically aligns all the neutron magnetic moments produc- ing a large magnetic field in the core. The accom- panying change of flux gives rise to shielding or screening currents in the surrounding high conduc- tivity plasma that do not permit the field to exit to the surface. Ambipolar diffusion then transports the field to the crust dissipating energy in neutri- nos and X-rays. The upwelling field cleaves the crust resulting in flares and X-ray radiation from Ohmic dissipation in the crust till the screening currents are damped and the surface polar field at- tains its final value. In the dynamo model, the polar magnetic field decreases with time, whereas in our screened model it increases to its final value. One consequence is that in the latter model, as a function of time and period, the ratio of the dipole radiation loss, E to the X-ray luminosity, LX, is a U curve, indicating that it is the exponential decline in LX that brings closure to the spin periods that are observed for magnetars. This work has been done in collaboration with Dipankar Bharracharya, Sameer Patel, Sajal Gupta, and Prasanta Bera. Parijat Thakur Investigating extra-solar planetary system Qatar-1 through transit observations We report the results of the transit timing variation (TTV) analysis of the extra-solar planet Qatar-1b using thirty eight light curves. Our analysis com- bines thirty five previously available transit light curves with three new transits observed by us be- tween June 2016 and September 2016 using the 2m Himalayan Chandra Telescope (HCT) at the Indian Astronomical Observatory (Hanle). From these transit data, the physical and orbital parame- ters of the Qatar-1 system are determined. In addi- tion, the ephemeris for the orbital period and mid- transit time are refined to investigate the possible TTV. We find that the null-TTV model provides the better fit to the (O-C) data. This indicates that there is no evidence for TTVs to confirm the pres- ence of additional planets in the Qatar-1 system. The use of the 3.6m Devasthal Optical Telescope (DOT) operated by the Aryabhatta Research In- stitute of Observational Sciences (ARIES, Nainital, India) could improve the photometric precision to examine the signature of TTVs in this system with a greater accuracy than in the present work. This analysis has been done in collaboration with V. K. Mannaday, I. Jiang, Devendra Kumar Sahu, and Swadesh Chand. Joint XMM-Newton and NuSTAR View of the ris- ing phase of the 2016 outburst of the low-mass black-hole X-ray binary H 1743-322 we have been working on the temporal and spectral study of the rising phase of the 2016 outburst of the low-mass black-hole X-ray binary H 1743-322 using the joint views by XMM-Newton and NuSTAR on March 13 and 15, 2016. H 1743-322 is a transient source and frequently shows outburst in the inter- val of ∼ 200 days. We have found low-frequency QPO along with an upper harmonic at around 0.95 and 1.15 Hz, respectively in the first observation. However, the same features are also present in the second observation but they are shifted to higher value, at ∼ 1.15 and 2.38 Hz, respectively. The inherent properties such as the quality factor and fractional rms amplitude of the QPO suggest the detected QPO to be of type C nature. We have also found that the shape of the PDS is indepen- dent of energy for both the observations. More- over, we have also studied the energy dependent variability of the characteristics frequency and the fractional rms amplitude of the QPO, upper har- monic, as well as the zero centered BLN (band lim- ited noise), which shows the lack of variability with the energy. The presence of broad iron line peaking at 6.8 keV and a reflection hump around 15-30 keV due to the Compton back-scattering is clearly visi- ble in the X-ray energy continuum. These features have been taken care with the relativistic reflec- tion model RELXILL along with the consideration for the thermal emission from the accretion disc ( 216 )