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      Permanent link:
      https://www.ias.ac.in/article/fulltext/joaa/042/0103

    • Keywords

       

      X-ray optics; soft X-ray telescope; Wolter type-I optics; AstroSat; X-ray astronomy.

    • Abstract

       

      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.

    • Author Affiliations

       

      VINITA NAVALKAR1 2 KULINDER PAL SINGH2 3 HARSHIT SHAH2 VILAS MHATRE2 VISHWAS RISBUD2

      1. Centre for Excellence in Basic Sciences, Vidyanagari Campus, Kalina, Santacruz (E), Mumbai 400 098, India.
      2. Tata Institute of Fundamental Research, Navy Nagar, Colaba, Mumbai 400 005, India.
      3. Indian Institute of Science Education and Research Mohali, Knowledge City, Sector 81, SAS Nagar, Ajitgarh, Punjab 140 306, India.

    • Dates

       
      Published
      17 September 2021
      Manuscript received
      6 August 2020
      Accepted
      22 March 2021
      Final version published online
      17 September 2021

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