AR-2019-2020

marks based on a popular scenario, namely, the minimal supersymmetric standard model. It is, thus, shown that the radio flux from a dSph like Draco should be observable in about 100 hours at the SKA, for dark matter masses upto 4-8 TeV. In addition, the regions in the space spanned by astro- physical parameters, for which such signals should be detectable at the SKA, are marked out. This work has been done in collaboration with Arpan Kar, Biswarup Mukhopadhyaya, and Tirthankar Roy Choudhury. Constraints on dark matter annihilation in dwarf spheroidal galaxies from low frequency radio obser- vations We present the first observational limits on the pre- dicted synchrotron signals from particle dark mat- ter annihilation models in dwarf spheroidal galax- ies at radio frequencies below 1 GHz. We use a combination of survey data from the Murchison Widefield Array (MWA) and the Giant Metrewave Radio Telescope to search for diffuse radio emis- sion from 14 dwarf spheroidal galaxies. For in situ magnetic fields of 1 μ G and any plausible value for the diffusion coefficient, our limits do not constrain any dark matter models. However, for stronger magnetic fields, our data might provide constraints comparable to existing limits from gamma-ray and cosmic-ray observations. Predictions for the sensi- tivity of the upgraded MWA show that models with dark matter particle mass up to ∼ 1 . 6 TeV (1 TeV) may be constrained for a magnetic field of 2 μ G (1 μ G). While much deeper limits from the future low frequency Square Kilometre Array (SKA) will chal- lenge the LHC in searches for dark matter parti- cles, the MWA provides a valuable first step toward the SKA at low frequencies. This work has been done in collaboration with Arpan Kar, Biswarup Mukhopadhyaya, Tirthankar Roy Choudhury, and Steven Tingay. Aditya Sow Mondal and Biplab Ray- chaudhuri Study of the reflection spectrum of the bright atoll source GX 3+1 with NuSTAR We report on the NuSTAR observation of the atoll type neutron star (NS) low-mass X-ray bi- nary GX 3+1 performed on October 17, 2017. The source was found in a soft X-ray spectral state with 3 − 70 KeV luminosity of L X ∼ 3 × 10 37 ergs s − 1 ( ∼ 16% of the Eddington luminosity), as- suming a distance of 6 kpc. A positive correla- tion between intensity and hardness ratio suggests that the source was in the banana branch dur- ing this observation. The broadband 3 − 70 KeV nustar spectral data can be described by a two- component continuum model consisting of a disk blackbody ( kT disc ∼ 1 . 8 KeV) and a single tem- perature blackbody model ( kT bb ∼ 2 . 7 KeV). The spectrum shows a clear and robust indication of relativistic reflection from the inner disc, which is modelled with a self-consistent relativistic reflec- tion model. The accretion disc is viewed at an inclination of i 22 − 26 degree and extended close to the NS, down to R in = (1 . 2 − 1 . 8) R ISCO ( 6 . 1 − 9 . 1 R g or 14 − 20 . 5 km), which allows an up- per limit on the NS radius ( ≤ 13 . 5 km). Based on the measured flux and the mass accretion rate, the maximum radial extension for the boundary layer is estimated to be ∼ 6 . 3 R g from the NS surface. However, if the disc is not truncated by the bound- ary layer but by the magnetosphere, an estimated upper limit on the polar magnetic field would be of B ≤ 6 × 10 8 G. This observation has been done in collaboration with Gulab C. Dewangan Pradip Mukherjee A new action for non-relativistic particle in curved background We obtain a new form for the action of a non- relativistic particle coupled to Newtonian gravity. The result is different from that existing in the lit- erature which, as shown here, is riddled with prob- lems and inconsistencies. The present derivation is based on the formalism of Galilean gauge the- ory, introduced by us as an alternative method of analysing non-relativistic symmetries in gravi- tational background. This work has been done in collaboration with Rabin Banerjee. Constrained Hamiltonian analysis of a non- relativistic Schrodinger field coupled with Chern- Simons gravity The coupling is achieved by the recently advanced Galilean gauge theory. The calculations are re- peated with a truncated model to show that de- viation from Galilean gauge theory makes the the- ory untenable. The issue of non-relativistic spatial diffeomorphism is discussed in this context. This