soxs_mbias¶

A zero-second exposure will contain only read-noise, and \(\sim\)half of the pixels within this Gaussian distribution centred around zero counts will always contain negative flux. To avoid negative counts, an offset bias voltage is applied at the amplifier stage so that even when no photons are detected, the A/D converter will always register a positive value. This bias-voltage offset must be accounted for in the data reduction process.

The purpose of the soxs_mbias recipe is to provide a master-bias frame that can be subtracted from science/calibration frames to remove the contribution of pixel counts resulting from the bias voltage.

Input¶

Table 45 Input files for the `soxs_mbias` recipe. The files are typically passed to the `soxs_mbias` recipe via a set-of-file (sof) file listing one file per line.¶
Data Type	Content	Related OB	Min. Frame Count
FITS images	raw bias frames (UV-VIS/AC exposures with exptime = 0)	`SOXS_img_cal_Bias`, `SOXS_gen_cal_VISBias`	5

Table 46 Ancillary (static) files required by the `soxs_mbias` recipe. These files are packaged with and shipped with the code.¶
Data Type	Content
FITS images	Default bad-pixel map

Parameters¶

Table 47 The `soxs_mbias` recipe parameters.¶
Parameter	Description	Type	Entry Point	Related Util
`frame_clipping_sigma`	number of \(\sigma\) from the median frame flux beyond which pixel is added to the bad-pixel mask	float	settings file	`clip_and_stack`
`frame_clipping_iterations`	number of \(\sigma\)-clipping iterations to perform when adding pixels to the bad-pixel mask	int	settings file	`clip_and_stack`
`stacked_clipping_sigma`	number of \(\sigma\) deviations from the median pixel flux beyond which pixel is excluded from stack	float	settings file	`clip_and_stack`
`stacked_clipping_iterations`	number of \(\sigma\)-clipping iterations to perform before stacking	int	settings file	`clip_and_stack`

Method¶

The purpose of the soxs_mbias recipe is to stack raw bias frames together (using the clip_and_stack utility) into master-bias frames, clipping rogue pixels from the individual raw frames and reducing the read-noise contribution. The algorithm used in the soxs_mbias recipe is shown in Fig. 35.

Fig. 35 The `soxs-mbias` recipe algorithm.¶

Output¶

Table 48 Output files for the `soxs_mbias` recipe and their respective ESO PRO keywords.¶
Label	Content	Data Type	PRO CATG	PRO TYPE	PRO TECH
`MBIAS`	Master bias frame (frame containing typical bias-voltage applied to the detector)	FITS image	`MASTER_BIAS_<ARM>`	`REDUCED`	`IMAGE`

QC Metrics¶

Table 49 Quality Control metrics calculated in the `soxs_mbias` recipe.¶
Label	Description	Unit	Acceptable Range
`BADPIX FRAC`	Fraction of bad pixels	-	-
`MBIAS MEDIAN`	Median flux level of master bias	electrons	VIS: [0, 2000]
`BADPIX NUM`	Number of bad pixels	-	-
`FPN FRACMAX`	Maximum periodic pattern noise ratio in raw bias frames	-	VIS: [0,3]
`RAW RON`	RON in single BIAS	electrons	VIS: [0,15]
`MASTER RON`	Combined RON in MBIAS	electrons	VIS: [0,10]
`STRUCTX`	Slope of BIAS in X direction	-	VIS: [-3,1]
`STRUCTY`	Slope of BIAS in Y direction	-	VIS: [0.0,0.6]