Slewing

The spacecraft will slew to a new target when directed to by the pre-programmed observing sequence. It will also slew to a new target whenever the BAT detects a new GRB with a FoM that is greater than that of the current observation.

The peak slew rate of the spacecraft is one degree per second, so XRT observations will typically begin approximately 90 seconds after the BAT trigger (median start time).

When a slew starts the XRT will end the current observation and start taking calibration frames. When these are complete, it will switch to Windowed Timing mode for the remainder of the slew. See the XRT Operation and Control section of this Technical Handbook for a description of the XRT's modes.

The UVOT will not collect data during a slew. When the slew is complete the UVOT requires three seconds to settle. During this period the target is in the UVOT's field of view, at which time observations will begin. However, the target's location is only known to BAT accuracy (3 arcminutes). The UVOT finding chart is not produced until after the UVOT has settled. The UVOT cathode voltage will ramp up during this period of settling, so photometry on this data can not be calibrated in the standard manner.