The data pipeline at the Payload Operation Centre (POC) of the Scanning Sky Monitor (SSM) onboard AstroSat involves: (i) fetching the Level-0 data from the Indian Space Science Data Centre (ISSDC), (ii) Level-0 to Level-1 data processing followed by Level-2 data generation, and (iii) transfer of theLevel-1 and Level-2 data back to ISSDC for dissemination of the re-packaged Level-2 data products. The major tasks involved in the generation of Level-1 and Level-2 data products are: (a) quality checks; time, alignment corrections, (b) temporal-HK plots generation, and, (c) image processing; light curve generation.The typical turn around time for this fully automated pipeline is about 25 min for one orbit data. In this paper, details of all the stages of this data pipeline are discussed.

SSM onboard AstroSat is designed to monitor X-ray sky in the energy range 2.5–10 keV to detect and locate X-ray sources in outburst. SSM with its three almost identical 1D-proportional counters mounted on a rotating platform, scans the sky in step and stare mode of operation. It observes the X-ray skyand generates light curves for X-ray sources detected. Here, we discuss the positional calibration to carry out imaging with SSM. Onboard calibration of SSM has been carried out with Crab, the standard X-ray source. SSM observations of Crab are compared with that of MAXI on ISS for cross calibration of the instrument.

The black hole binary source Swift J1753.5--0127 remained in outburst for $\sim$12 years from May 2005 to April 2017. For the most part of the outburst, the source remained in the low hard state (LHS) displaying transitions to softer states only towards the end of the outburst for short periods of time. Quasiperiodic oscillations (QPOs) were observed in the power density spectrum (PDS) only during the decay. A soft thermal component was required to model the spectrum in LHS, which does not conform to the generally accepted disc truncation theory. In this work, we attempt to obtain a clearer picture of the accretion disc geometry by studying the QPO variability using frequency-resolved spectroscopy (FRS). We obtain the QPO rms spectrum of the source during the bright-hard state and model it with physical components. We findthat the QPO rms spectrum can be described only by a Comptonization component with no contribution from the thermal disc. This indicates that the variability observed in the PDS originates in the Comptonizationcomponent and the evolution of the QPOs is likely to be a result of localization of the variabilities to different radii of the hot inner flow rather than disc truncation. The minimal variation in disc parameters also points to the existence of a stable disc throughout the outburst.