DR. VIKRAM RANA

The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first mission to carry focusing high-energy X-ray telescope in space. NuSTAR, with its unprecedented combination of sensitivity, spatial and spectral resolution, turned out to be an ideal observatory to probe the hard X-ray properties of Ultraluminous X-ray sources (ULXs) and Cataclysmic Variables (CVs) as well as other X-ray binaries. ULXs are of prime interest, as they may be associated with a poorly explained regime of super-Eddington accretion onto a stellar mass black hole (BH), or even contain sub-Eddington intermediate mass BHs. Broad-band X-ray study of a sample of bright ULXs with XMM-Newton and NuSTAR revealed that all the sources in the sample show a clear cutoff at or above ~10 keV, strongly suggesting different physical origin for their X-ray emission compared to Galactic black hole X-ray binaries and supporting exotic super-Eddington modes of accretion. CVs, on the other hand, contain an accreting white dwarf as a compact object. NuSTAR provided a first direct detection of reflection component in three magnetic CVs, namely, V709 Cas, Ny Lup and V1223 Sgr. In the past, there was only an indirect evidence for the existence of reflection component based on presence of Fe fluorescence line. NuSTAR observations provided an important piece of information required to obtain a complete picture of these magnetic CVs. During this talk, the speaker will discuss recent interesting science results on ULXs and CVs using hard X-ray data from NuSTAR and simultaneous soft X-ray coverage with XMM-Newton and Suzaku.