Additional Calibration of the Ultraviolet Imaging Telescope on Board AstroSat

Abstract

Results of the initial calibration of the Ultra-Violet Imaging Telescope (UVIT) were reported earlier by Tandon et al. (2017a). The results reported earlier were based on the ground calibration as well as the first observations in orbit. Some additional data from the ground calibration and data from more in-orbit observations have been used to improve the results. In particular, extensive new data from in-orbit observations have been used to obtain (a) new photometric calibration which includes (i) zero-points (ii) flat fields (iii) saturation, (b) sensitivity variations (c) spectral calibration for the near Ultra-Violet (NUV; 2000−3000Å) and far Ultra-Violet (FUV; 1300−1800Å) gratings, (d) point spread function and (e) astrometric calibration which includes distortion. Data acquired over the last three years show continued good performance of UVIT with no reduction in sensitivity in both the UV channels.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

“…IC 3476 has been observed with ASTROSAT/UVIT (Agrawal 2006;Tandon et al 2020) in May 2020 using the FUV filter BaF2 (λ c = 1541 Å; ∆λ = 380 Å) during a run dedicated to the observation of a representative sample of Virgo cluster galaxies (proposal A08-003: A FUV Survey of Virgo Cluster Galaxies, PI: J. Hutchings). The observations were carried out with an integration of 12 453 s, reaching a typical surface brightness of µ(FUV) 26.8 AB mag arcsec −2 .…”

“…The field of view of the instrument has a diameter of 28 and an angular resolution of 1.5 . The data were reduced following the prescriptions given in Tandon et al (2020) using a zero point of z p = 17.771 mag and the astrometry was checked against the accurate NGVS data (Ferrarese et al 2012, see below).…”

ASTROSAT/UVIT Near and Far Ultraviolet Properties of the M31 Bulge

“…The systematic errors in converting counts/s to flux or magnitude ([11] and[10]) are small compared to the 1 N statistical errors for these narrow (1 pixel wide) elliptical areas. data, in units of flux per pixel (erg•cm −2 •s −1 •A −1 •pixel −1 ), we use units of pixels for a.…”

“…The bulge of M31 was observed by UVIT in 2017 [5] and at a second epoch in 2019. New in-orbit calibrations of the UVIT instrument have been carried out by [11] and are applied here to the 2017 and 2019 observations.…”

“…Merged images, here labelled "M", were produced for filters F172M and F148W which had data from both A and B epochs. The merged images were created by adding the counts images for A and B, adding the exposure maps for A and B, then dividing the counts images by the exposure images to create a count/s image from which fluxes can be extracted using the UVIT calibrations (updated in [11]).…”