Overview of UVOT

The UVOT (Roming, et al. 2005, SSRv, 120, 95) is a modified Ritchey-Chrétien telescope with a 30 cm aperture and an f-number of f/12.72. It operates in the wavelength range of 1600-6000 Å, although there is some low-level response in between 6000 Å and 8000 Å. It is mounted on the optical bench with the BAT and the XRT as shown in Figure 8 and co-aligned with the XRT. An 11-position filter wheel houses the UV and optical grisms, a 4-times magnifier, broadband UV and optical filters, a clear ``white-light'' filter, and blocking filter. Photons register on a micro-channel plate intensified charged-coupled device. These can operate in a photon counting mode and are capable of detecting very low light levels. When flown above the atmosphere the UVOT possesses the equivalent sensitivity of a 4 m ground-based telescope, capable of detecting a 22nd magnitude B star in 1000 seconds using the white-light filter. An outline of the UVOT's characteristics can be found in Table 7.

Figure 9: UVOT's placement on the Swift optical bench.

Table 7: Characteristics of the UVOT.

UVOT Parameter	Value
Telescope	Modified Ritchey-Chrétien
Aperture	30 cm diameter
f-Number	f/12.72
Detector	Intensified CCD
Detector Operation	Photon Counting
Field of View	$17 \times 17$ arcminutes
Detection Elements	$256 \times 256$ pixels
Sampling Elements	$2048 \times 2048$ pixels after centroiding
Telescope PSF	approximately 2.5 arcseconds FWHM
Wavelength Range	1600-6000 Å
Filters	11
Sensitivity	B = 22.3 in white light in 1000 s
Virtual Pixel Scale	0.502 arcseconds
Timing Resolution	11.0329 ms
Gain	1.0 count ADU$^{-1}$
Readout Noise	0.0 count s$^{-1}$ pixel$^{-1}$
Dark Current	$7 \times 10^{-5}$ count s$^{-1}$ pixel$^{-1}$