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We report on the 2016 outburst of the transient Galactic Black Hole candidateIGR J17091-3624 based on the observation campaign carried out with SWIFT andNuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical`q'-shape in the Hardness Intensity Diagram (HID). Based on the spectral andtemporal evolution of the different parameters, we are able to identify all thespectral states in the q-profile of HID and the Hardness-RMS diagram (HRD).Both XRT and NuSTAR observations show an evolution of low frequency Quasiperiodic oscillations (QPOs) during the low hard and hard intermediate statesof the outburst rising phase. We also find mHz QPOs along- with distinctcoherent class variabilities (heartbeat oscillations) with differenttimescales, similar to the $\rho$-class (observed in GRS 1915+105).Phenomenological modelling of the broad-band XRT and NuSTAR spectra alsoreveals the evolution of high energy cut-off and presence of reflection fromionized material during the rising phase of the outburst. Further, we conductthe modelling of X-ray spectra of SWIFT and NuSTAR in 0.5 - 79 keV tounderstand the accretion flow dynamics based on two component flow model. Fromthis modelling, we constrain the mass of the source to be in the range of 10.62- 12.33 Msun with 90% confidence, which is consistent with earlier findings.

Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst : SWIFT and NuSTAR results