Photometric Calibration of the Swift Ultraviolet/Optical Telescope

Understand

We present the photometric calibration of the Swift UltraViolet/Optical Telescope (UVOT) which includes: optimum photometric and background apertures, effective area curves, colour transformations, conversion factors for count rates to flux, and the photometric zero points (which are accurate to better than 4 per cent) for each of the seven UVOT broadband filters.

• The calibration was performed with observations of standard stars and standard star fields that represent a wide range of spectral star types.
• The calibration results include the position dependent uniformity, and instrument response over the 1600-8000A operational range.
• Because the UVOT is a photon counting instrument, we also discuss the effect of coincidence loss on the calibration results.