The Soft X-ray Telescope (SXT) aboard the AstroSat satellite is the first Indian X-ray telescope in space. It is a modest size X-ray telescope with a charge coupled device (CCD) camera in the focal plane, which provides X-ray images in the $\sim$0.3–8.0 keV band. A forte of SXT is in providing undistorted spectraof relatively bright X-ray sources, in which it excels over some current large CCD-based X-ray telescopes. Here, we highlight some of the published spectral and timing results obtained using the SXT data to demonstrate the capabilities and overall performance of this telescope.

Soft X-ray telescope (SXT) built on the principle of grazing incidence optics was launched onboard AstroSat on September 28, 2015, and made operational on October 26, 2015. The telescope optics consists of two conical sections of approximate paraboloid and hyperboloid mirror segments arranged in Wolter type-I design. It comprises a total of 320 mirror segments made from aluminum foil of 0.2 mm thickness coated with gold on the front (reflective) side by the replication process that was first used in the Suzaku Observatory. The mirrors focus X-rays in the energy range of 0.3–8.0 keV on to a charged coupleddevice-based focal plane camera assembly at a distance of 2 m. We present here the pre-launch, groundbased calibration, and evaluation of SXT optics carried out at the X-ray Optics Laboratory at the Tata Institute of Fundamental Research. The SXT optics assembly was calibrated and evaluated experimentally, using scans by a collimated optical beam from a laser source, as well as using a full-aperture optical beam from an inverse telescope. A collimated beam of a red laser source was used to ensure the accuracy of mounting of individual mirror segments and the full aperture beam white light-emitting diode (LED) source was used to estimate the point spread function (PSF) of all 320 mirrors together. The approximate PSF obtained during the ground calibration was around 136.6 arcsec. These results were in accordance with theresults obtained during the in-orbit calibration post launch.

In this article, first the author present a short historical introduction to the discovery of extragalactic jets in active galactic nuclei (AGN), followed by a brief overview of their observational properties which lead to their various classifications and a unification scheme based on the viewing geometry of jets in the AGN. The author largely focus on the studies of multi-wavelength emissions and modeling of spectral energy distribution of AGN, which are dominated by emission from jets, namely, blazars. The author present a few new results from the studies of a few blazars based mostly on observations with the AstroSat. The author ends with an overview of the role played by the radio jets in clusters of galaxies in creating various interesting features in the hot gas, and feedback and regulation of heating and cooling in the cores of the hot gas.