Detailed description of photometer sensitivity calculations and sensitivity numbers are provided in the corresponding Observers' Manuals (see PACS Observers' Manual Section 3.4.4 and SPIRE Observers' Manual Chapter 3).
In this section, sensitivity numbers are given specific for the Parallel Mode (Table 2.1). The Parallel Mode AOT (see section 2.5) allows to influence the depth of the observation only in one way: the observer can only choose the scan speed: 60"/s (fast mode) or 20"/s (slow mode). In Table 2.1, the second column summarizes sensitivities for the fast mode and the third column reports sensitivities for the deeper slow mode. To a first order, the sensitivity in scan mode scales with the inverse of the square root of the on-source observation time (the source crossing time), therefore the gain in depth if changing from fast to slow mode is about a factor of 1.7.
Table 2.1 reports 1-σ instrument noise for a point source: values are applicable to all Parallel Mode observations irrespective of the map size. Note the difference between "Nominal" and "Orthogonal" scan directions, due to the different scan leg separation (see Section 2.9)
Table 2.1. The SPIRE PACS Parallel Mode 1-σ instrument noise for a point source, calculated for the two scan speeds and for a single map coverage. Units are mJy in beam.
Scan direction | Nominal | Orthogonal | ||
|---|---|---|---|---|
Scan speed | 60"/s | 20"/s | 60"/s | 20"/s |
SPIRE 500 µm | 15.0 | 8.7 | 14.4 | 8.3 |
SPIRE 350 µm | 10.5 | 6.0 | 10.0 | 5.8 |
SPIRE 250 µm | 12.6 | 7.3 | 12.1 | 7.0 |
PACS 130-210 µm | 47.0 | 27.3 | 45.2 | 26.3 |
PACS 85-130 µm | 24.7 | 14.3 | 23.8 | 13.8 |
PACS 60-85 µm | 21.0 | 12.2 | 20.2 | 11.7 |