PVPhotFlux PACS Photometer photometric calibration MPIA PACS Commissioning and PV Phase Plan Review 21 st – 22 nd January 2009, MPE Garching Markus Nielbock (MPIA) Marc Sauvage (CEA/SAp)

M. Nielbock, M. Sauvage – PVPhotFlux Instrumental background PACS photometer (PHOT) two bolometer arrays – blue detectors: 4 x 2 matrices of 16 x 16 pixels – red detectors: 2 matrices of 16 x 16 pixels additional optical elements – filter wheel – mirrors (external and internal) – chopper

M. Nielbock, M. Sauvage – PVPhotFlux PHOT photometric calibration topics PACS Calibration Document (PCD) requirements 3.2 mainly covered by observations of PVPhotFlux proposal partly fulfilled by interdependent PCD requirements partly covered by related observations of other PV PHOT proposals

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Determination of detector responsivity establish relation between voltage output and absolute sky brightness internal calibration sources (CS), celestial standards measure irradiation power vs. detector signal fully covered by PVPhotBol (PHOT detector characterisation)

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Monitor stability of detector responsivity identify amplitude and timescales of responsivity drifts possible significantly contributing sources: – internal stray light (incl. self-emission) – temperature changes between individual cooling cycles – variation in efficiency of cryo pumping – bias voltage supply – thermal conductance – particle irradiation – interference by other satellite components calibration targets used: – internal CS – stable celestial flux standard (S/N ≥ 20), repeatedly during PV phase

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Monitor stability of detector responsivity Implementation: – internal CS ◦ calibration block during slew to target prior to AOR execution ◦ chopping between two CSs having different temperatures ◦ minimised or no down time for satellite – celestial flux standard ◦ point-source AOR on ε Car (5 repetitions, always visible, ~10 Jy) ◦ estimated time required: 0.5 h Status: fully defined and implemented Analysis: SPG (pipeline), additional work based on SOVT-2 results

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Calibrate non-linearity characterise the non-linear range of PHOT detectors non-linearity for very bright sources calibration targets: very bright flux standards (e.g. bright stars, asteroids) Implementation: – point-source photometry with reduced gain (avoid electronic saturation) – flux grid of celestial flux standards (2, 10, 50, 200, 500, 1000 Jy) – measure all three filters (simultaneous coverage where possible) – accuracy goal: S/N ≥ 30 – caveat: difficult to find bright and non-variable sources – estimated time required: 1.3 h Status: fully defined and implemented (some discussion on target selection) Analysis: SPG (pipeline), additional work based on SOVT-2 results

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Establish full system linearity calibrate the linear approximation verify valid flux range of linear approximation of detector response calibration targets: celestial flux standards Implementation: (similar to PCD req ) – point-source photometry with default gain setting – flux grid of celestial flux standards (20 mJy to 200 Jy) – measure all three filters (simultaneous coverage where possible) – accuracy goal: S/N ≥ 30 – estimated time required: 5.0 h Status: fully defined and implemented Analysis: SPG (pipeline), additional work based on SOVT-2 results

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Noise and minimum detectable flux establish NEP depending on detector biasing internal calibration sources fully covered by PVPhotBol (PHOT characterisation) independent confirmation of minimum flux may be desirable – not only depends on detector properties – easy to implement (standard point-source AOT) – easy to analyse (SPG, pipeline) – suitable weak calibration targets from ISO GBPP / ISOPHOT Cohen – observe set of targets to minimise impact of flux uncertainties – estimated time required: approx. 10 h

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Full system flat field determine (in)homogeneity of PHOT FOV and temporal variation detector and optical flat field indistinguishable calibration targets: internal CS, point source or small extended source Implementation: – internal CS ◦ calibration block during slew to target prior to AOR execution ◦ chopping between two CSs having different brightness (temperatures) ◦ minimised or no down time for satellite ◦ individual CS illumination pattern available from FOV scans

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Full system flat field Status: fully defined and implemented – celestial flux standard ◦ scan map AOR all three filters on NGC 6543 and Arp 220 ◦ covering all detector pixels redundantly ◦ estimated time required: 2.9 h Implementation: Analysis: SPG (pipeline), additional work based on SOVT-2 results

M. Nielbock, M. Sauvage – PVPhotFlux PCD req Telescope background and stability telescope will be major flux source determine spatial and temporal stability of telescope contribution assessed by frequent field-of-view scans with chopper fully covered by PVPhotSpatial fulfilled by PCD req (FOV characterisation)

M. Nielbock, M. Sauvage – PVPhotFlux Summary PV plan regarding the photometric calibration of the PACS photometer is fully prepared as it is currently defined. All relevant calibration requirements (PCD) are met. required observation time in total: 9.6 h Interdependent requirements are partly covered by different calibration programmes (PVPhotBol, PVPhotSpatial). Optional additional observations (lower flux limit check) are easy to implement and may add another 10 hours.