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Any system which will be dedicated to the search for simultaneouls optical counterparts of GRBs must adhere to unique design requirements which may include:

LOTIS Single Camera Assemble

  1. A large field-of-view in order to maximize the probability of covering the entire 3-sigma error box.
  2. High sensitivity in order to maximize the probability of detecting optical emmission or to place tight constraints on GRB central engine models.
  3. Complete automation in order to respond rapidly to a GRB trigger while gamma-rays are still being emitted.
  4. Low cost in order to efficiently use the available funding.

The LOTIS system utilizes short focal length optics to maximize the field-of-view. The telescope consists of a 2 x 2 array of commercially available Canon EF 200 mm f/1.8L telephoto lenses. Each lens has an effective aperture of 11.1 cm (4.37 in) with a unique multi-element design which corrects for both spherical and chromatic aberation. Guassian fits to the image of a point source yielded an average 1-sigma width of 6 microns at the focal plane.

LOTIS Four Camera Assemble
The LOTIS cameras use Loral 442A 2k x 2k CCDs as the imaging sensors. These CCDs provide a focal plane area of 3.1 cm x 3.1 cm which coupled with the optics corresponds to a field-of-view for each camera of 8.8° x 8.8°. The total field-of-view for the telescope array (allowing for overlap) is therefore 17.4° x 17.4°. The CCD pixel size of 15 µm x 15 µm results in a pixel resolution of 15 arcsec.

The readout electronics were designed and fabricated at LLNL. In addition to the CCD board each camera enclosure houses a ADC (Analog-to-Digital Converter) board and a computer control board.

LOTIS Loral CCD The CCD board consists of a socket for the CCD, clock drive circuitry, the first stage signal amplifier/buffer, and a temperature monitor. The clock drive voltages are regulated with levels that are resistor programmable. The aplifier gain value was selected to obtain the optimum desired sensitivity for the CCD. The amplifier provides a low impedance drive of the CCD signal which is routed to the ADC board.
The ADC board provides the second stage signal amplification, CDS (Correlated Double Sampling) circuitry, and analog-to-digital conversion. The 12 bit ADC sampling rate is fixed at 500k samples/sec as a compromise between low noise operation and CCD readout speed. This sampling rate results in an 8 second readout time. The parallel digital output of the ADC is buffered and routed to the computer control board.

The computer control board provides all the control signals for the CCD and ADC boards.

LOTIS Clamshell Housing
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