Frequency-Time Image Handling

   

An optional output from the MAKE/POWER_SPECTRUM command (option SEGMENTED) is the so-called -T image, consisting of the single power spectra obtained in the accumulation, reported vs. time. The format of this image is described in section 7.2.8. Since its structure is not suitable for display and plot, some additional commands are available to transform, plot and display this image.

The command PREPARE/POWER_IMAGE takes in input the rough -T image which comes in output from the command MAKE/POWER_SPECTRUM (SEGMENTED option) and creates a 512   512 pixels image for display (converted into rms units). Many options are available to preprocess the image: it is possible to remove bad spectra, to perform a rebinning and/or a smoothing on both coordinates independently, to subtract a given power law and to identify gaps in the time coordinate. The output will be a MIDAS bulk data frame divided into two windows: in the left window the power data (converted to rms) are reported, and in the right one is displayed the light curve. WARNING! This image is not suitable for analysis, and it should be used only for display. The syntax of the command is:

PREPARE/POWER_IMAGE parfil

where parfil is the name of the parameter file generated using CREATE/PARFIL IPOWER. The parameter file entries are shown in Table 7.16.

  
Table 7.16: Parameter file entries for PREPARE/POWER

The meaning of the parameters is as follows:

• INPUT_FILENAME is the name of the input image (output from the command
  MAKE/POWER_SPECTRUM, option SEGMENTED). The default extension is BDF.
• OUTPUT_FILENAME is the name of the output table, which can be directly displayable with LOAD/IMAGE. The default extension is BDF.
• N_OF_BAD_COLUMNS is the number of the group of spectra which must be excluded from the output image (e.g. corresponding to corrupted spectra). The default value is 0 (no bad spectra): in this case the parameter BAD_INDEX_WIDTH_n is not read in.
• BAD_INDEX_WIDTH_nn is a two (integer) values parameter. The first value is the position (number of the spectrum as in the logfile in output from MAKE/POWER_SPECTRUM option SEGMENTED) of the first spectrum of the ``bad group'' nn. The second value is the number of spectra constituting the bad group. There is no default: these parameters are read in only if a non-zero value is specified for N_OF_BAD_COLUMNS.
• MINIMUM_GAP_LENGHT is the minimum length for a time gap in ordered to be identified by the program. A identified gap is marked in the output image with a white line. The default value is  (no gaps will be identified).
• TIME_REBIN_FACTOR is the rebinning factor in time. The default value is 1 (no rebinning).
• FREQUENCY_REBIN_FACTOR is the rebinning factor in frequency. The default value is 1 (no rebinning).
• TIME_SMOOTHING is the time smoothing factor specifying the half size of the smoothing window. The default value is 0 (no smoothing).
• FREQUENCY_SMOOTHING is the frequency smoothing factor specifying the half size of the smoothing window. The default value is 0 (no smoothing).
• WHITE_NOISE_LEVEL is the white noise level to be subtracted. from the image values. Since the output image is converted in rms units, it is advisable to subtract the white noise. The default is 2.
• POWER_LAW_PARAMS are the parameters of a power law which is subtracted from all the spectra in the output image. The parameters are normalization (in power) and slope respectively. If no power law subtraction is desired, this parameter should not be specified in the parameter file.
• MAXIMUM_POWER is the value of the maximum value of rms for image normalization purposes. The user should run the command once for test in order to determine the maximum value of the output image and then tune this parameter in a second run. The default value is 0.2
• Y_MAXIMUM is the maximum number of image rows to be used in the output bulk data frame (it should be less than 512). Since the image is blown up both in X- and Y-direction to fill the whole image (512 512), the user might want to stop the blow up in the Y-direction (time axis) to some value. Use the value 512 (default) to fill the whole image.
• Format of the input: the files input to this command are:
  • PARAMETER FILE: standard ASCII file. Its general format is described in Table 7.16.
  • ROUGH -T IMAGE: it is the output from MAKE/POWER_SPECTRUM S.
• Format of the output: the files in output from this command are:
  • FINAL -T IMAGE: The value for the power are already normalized between 0 and 256. The cuts are selected in order to have the frame with the overlay bits on, so that any change of the lookup table will not affect the frame. The right window shows the count rate as a function of time (count rate on the X-axis and time on the Y-axis). Tics are marked only for the count rate axis. No labels are displayed: lower/upper values and step for the count rate tics are reported in the logfile (and to the terminal).
  • LOGFILE: it is an ASCII file containing a copy of the output to terminal. The useful parameters read in from the parameter file are reported. Then for all the time steps the index (row number), the corresponding time (in units of 100s), count rate and average power are displayed. Following are reported the mean power and variance, the number and power of the spectra with power out of 5  from the total average (they are only identified and it is possible to remove them in a following run of the command), the informations about the number of continuous intervals found (according to the minimum gap size defined by the user). Then follow the statistics of the image, namely: minimum and maximum count rates, the minimum and maximum times (in units of 100s), the minimum and maximum power and the new minimum and maximum power (i.e. after the whole processing). The last informations in output are the X and Y blow up factors (i.e. the X and Y sizes of the power pixels in units of true pixels) and the start/end/step for the count rate tics. The logfile has the standard name ps_ima.log