10.1.3 Filters

Imaging with HAWC+ can be performed in either TOTAL INTENSITY or POLARIZED INTENSITY modes. The dual-beam nature of HAWC+ allows simultaneous measurement of both total and unpolarized intensity (Stokes parameters I, Q, and U) in the POLARIZED mode since the total intensity is given simply by the sum of the signal in the two polarization beams (neglecting circular polarization). The HWPs that allow modulation of the polarization can also be removed from the optical path such that the beam passes through an open pupil for TOTAL mode. There is a slight gain in total sensitivity in this mode as the HWP transmission is < 100% and additional overhead is required to account for rotating the HWP.

Both observing modes can utilize any one of five optical filters. Each passband includes a bandpass filter and a number of low-pass cut-off filters. Figure 10-2 shows transmission profiles including all filters for all bandpasses. The effective wavelengths and bandwidths averaged over the total filter transmission are given in Table 10-1.

HAWC+ filter transmission profiles

Figure 10-2: HAWC+ filter transmission profiles.

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