CEA DSM Dapnia SAp Flux calibration of the Photometer Koryo Okumura, Marc Sauvage, Nicolas Billot, Bertrand Morin DSM/DAPNIA/Sap

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer2 Stable signal for a better photometry How stable is the signal? –Response? –Offset? Response variation is quite small – less than 0.1% Offset is the main component of the drift seen in the noise spectral density –about some hundreds of micro volts in 3 hours

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer3 Response and offset monitoring

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer4 Drift seen in low frequency measurements

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer5 Linearity and non-linearity of the response 1 % of responsivity loss for ≈ 0.1 pW/pixel ≈ 3 Jy/pixel

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer6 Flat field derivation using data from ILT3 (1) OGSE BBCS2CS1 Chopper scan Median value for each pixel on this interval 2 OGSE BB fluxes 2 median images 1 responsivity image Responsivity =, Flat_field = Responsivity image Responsivity

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer7 Flat field derivation using data from ILT3 (2) Chopper scan on OGSE of the field of view measurements are used Median 2D image is considered to have a flat flux level at the central chopper interval Difference of 2 median images of different fluxes (pixel to pixel response to a uniform brightness distribution through the central field-of-view distortion) This divided by the flux difference computed from OGSE temperatures provides a pixel to pixel responsivity 2D map The average over the valid pixels gives the mean responsivity (scalar) and the flat field

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer8 Field of view measurements during ILT3 Blue with 2 different filters T_ogse [kelvin] 70 um [pW/pixel] 100 um [pW/pixel] dFlux [pW/pixel]

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer9 Flux difference on the blue detector with 2 different filters and different OGSE temperatures Flux 1 [pW/pixel]Flux 2 [pW/pixel]dFlux [pW/pixel]

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer10 Flux difference on the red detector with 2 different OGSE temperatures Flux 1 [pW/pixel] Flux 2 [pW/pixel] dFlux [pW/pixel]

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer11 Noise propagation in the photometry Signal = flat_field x Flux + offset dSignal = flat_field x dFlux Each time we do a multiplication or division, a relative variance is added dFlux should be large to reduce the noise, but should be small enough to stay within the valid linear range

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer12 Which responsivity and flat field to use? Standard flat field and CS flux: –OGSE flat field : dSignal / dFlux –CSs flux : dSignal / flatField Calibration block flat field: –CSs flat field : dSignal / dFlux Calibration blockObservationCalibration block

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer13 How do we use the CS calibration blocks? Standard flat field Flux = Signal / OGSE_flat_field Sum of relative variances of : –OGSE flux –OGSE signal –Data signal CSs flat field Flux = Signal / CSs_flat_field Sum of relative variances of : –OGSE flux –OGSE signal –Cal CSs signal –Data CSs signal –Data signal

CEA DSM Dapnia SAp November 8th Koryo Okumura - PACS Sience Verification Review (Phase MPE Garching) : Flux calibration of the Photometer14 Flat field and responsivity as calibration file The standard flat field should be used for the flux calibration of the data The flat field depends on the flux level We need flat fields with low noise The flat field has to be interpolated from available flux level to a real background flux level Flat field of the red detector contains the electrical cross-talk Flat field of the red detector is a poor quality because of the offset drift in the measurements How can we measure in orbit a good flat field, if necessary?