for all ACIS observations (including TG) we moved from 8"x8" to 16x"16"
starting cycle 25 and for some cycle 24 observations.
We started using this occasionally with the PEA Patch ~ May 18. It is now the default for Cycle 25.
From the POG:
6.12 Dither
Unless specially requested, the spacecraft is dithered in a Lissajous pattern during all observations. For observations with ACIS, the default dither pattern now spans 32 arcsec peak to peak in both the Y and Z directions. Note that for subarrays smaller than 126 pixels, the dither spans 32 arcsec peak to peak in the long direction, but only 16 arcsec peak to peak in the short direction. The dither serves two purposes: (1) to provide some exposure in the gaps between the CCDs, and (2) to smooth out pixel-to-pixel variations in the response. The effect of dither is removed during high-level ground processing of the data. The exposure time in the gaps between chips (and at the outside edges) will be less than that for the remainder of the field. Default dither parameters are listed in Table 5.4.
From Scott Wolk:
for all ACIS observations (including TG) we moved from 8"x8" to 16x"16" starting cycle 25 and for some cycle 24 observations.
We started using this occasionally with the PEA Patch ~ May 18. It is now the default for Cycle 25.
From the POG: 6.12 Dither Unless specially requested, the spacecraft is dithered in a Lissajous pattern during all observations. For observations with ACIS, the default dither pattern now spans 32 arcsec peak to peak in both the Y and Z directions. Note that for subarrays smaller than 126 pixels, the dither spans 32 arcsec peak to peak in the long direction, but only 16 arcsec peak to peak in the short direction. The dither serves two purposes: (1) to provide some exposure in the gaps between the CCDs, and (2) to smooth out pixel-to-pixel variations in the response. The effect of dither is removed during high-level ground processing of the data. The exposure time in the gaps between chips (and at the outside edges) will be less than that for the remainder of the field. Default dither parameters are listed in Table 5.4.