EXSAS Standard Headers

 

  
Table C.1: EXSAS General Header

  
Table C.2: EXSAS Special Header for filetypes PET and PEM

Notes:

1. The TIM_SEL descriptor provides the selected time intervals for the photons listed in the PET. Each time interval is defined by its start value (odd positioned elements in the descriptor) followed by its end value, expressed in the same units used for the TIME photon parameter.

   The listed selected times are the result of the intersection between the original (instrumental) accepted times and all the time selections specified by the user on the photon list.

   Up to 16384 selected time intervals may be stored in the descriptor. A similar meaning have the RAW_SEL and AMP_SEL descriptors for the selections in non-calibrated and calibrated photon amplitudes, respectively.

2. A history of different spatial selections cannot generally be expressed in a simple form. Since no mask images are created for the spatial selections, it is necessary to provide the information as a sequence of elementary spatial selections performed over the original photon event list.

   In the character descriptor SPA_SEL_SEQ the presentation points to the elementary spatial selections described explicitly in the SPA_SEL_TYP and SPA_SEL_PAR descriptors. The symbols + and : represent union and intersect operations between the elementary spatial selection applied to the data, while the symbol # is used as a field delimiter between independent selection groups.

   However, it is not necessary for the general user to understand the meaning of the SPA_SEL_*** descriptors, because they are automatically composed, written out, read and interpreted by the appropriate Data Preparation tasks.

3. This character descriptor, together with the SPA_SEL_PAR, is used to describe all the elementary spatial selections composing the selection sequence which brought to the photon list contained in the PET. A letter ``B'' at position n indicates that the n-th elementary selection is a BOX selection, a letter ``R'' indicates a RING selection, and a letter ``S'' indicates a SECTOR selection.
4. This descriptor, together with the SPA_SEL_TYP, is used to describe all the elementary spatial selection composing the spatial selection history which brought to the photon list contained in the PET. The listed numbers must be taken in groups of 4 elements, each group corresponding to one character in the SPA_SEL_TYP descriptor. When the corresponding character is ``B'', the 4 elements of the group represent the X,Y coordinates at the lower left and upper right corners of the selected box. When the corresponding character is ``R'', the 4 elements of the group represent the central X,Y coordinates and the internal and external radii of the selected ring. When the corresponding character is ``S'', the 4 elements of the group represent the vertex X,Y coordinates and the start-end angles of the sector.
5. Smallest box on the sky containing all the events belonging to the PET. It is described by its lower left and upper right corner in sky coordinates. The descriptors associated to spatial selection operations, SPA_SEL_SEQ, SPA_SEL_TYP, SPA_SEL_PAR and SKY_FIELD, refer all to selections of photons over their sky pixels positions. Exactly the same meaning have the descriptors DET_SEL_SEQ, DET_SEL_TYP, DET_SEL_PAR and DET_FIELD, regarding to selections in detector pixels.

  
Table C.3: EXSAS Special Header Extension for filetype PEM

For PEM tables this extension is used in addition to table C.2

  
Table C.4: EXSAS Special Header Extension for filetype PET when more than one photon list is present

Notes:

1. A PET may contain more than 1 separate photon lists. The descriptor
   NUM_DATASETS from the general EXSAS header gives the number of independent photon lists contained in the PET. The PET column labelled ID, used for the identification of photons belonging to different lists, will show integer values in the range 1, ..., NUM_DATASETS. The descriptor START_DATASETS has NUM_DATASETS elements and contains the table row numbers at which each of the independent photon lists starts, once the table was sorted according to the ID column. Because the first photon list starts at the first table row, it is always START_DATASETS(1) = 1. The difference START_DATASETS(n+1) - START_DATASETS(n) returns the number of photons belonging to the n-th independent list. For the last independent photon list (n = NUM_DATASETS) the number of photons is given by TBLCONTR(4) - START_DATASETS(n) + 1.
2. Here the final exposure time, result of all the time-selections applied to the data (including the instrumental accepted times), is given for each of the NUM_DATASETS data sets included in the file. Please, note that this exposure time is not dead time corrected. Moreover, if the source of interest was not always kept inside the detector, the exposure time is overestimated. The calculation of the true exposure time is performed by the correction task (in attitude mode) where the descriptor TIM_INT is updated accordingly. Similar meaning have the RAW_INT, AMP_INT and SPA_INT descriptors for pulse height, calibrated pulse height and spatial selections, respectively.
3. The area of the selected spatial dominion is expressed in sky pixel.
4. The area of the selected spatial dominion is expressed in detector pixel.

  
Table C.5: EXSAS Special Header for filetype BIN

Notes:

1. The SPA_SEL_SEQ1,2,3,... SPA_SEL_TYP1,2,3,... and SPA_SEL_PAR1,2,3,... parameters contain history of spatial selections in sky pixels for each of the binned data sets in the table. Their structure is identical to the structure of the corresponding descriptors of the PEM and PET Headers.
2. The TIM_SEL1, TIM_SEL2, etc., descriptors contain the accepted times for each of the binned data sets in the table. Their structure is identical to the structure of the TIM_SEL descriptor of the PEM and PET. In case of a light curve the single descriptor TIM_SEL is given in phase (valid for all light curves included in the BIN table).
3. If the VIGCOR descriptor is present, and set to 1, it means that the current BIN table was created through Projection set in correction mode. In order to ignore the correction on the data, just set this descriptor value to 0, or delete the descriptor itself.
4. If the DTCOR descriptor is present, and set to 1, it means that the current BIN table was created through Projection set in correction mode, and the dead time correction was also performed. In order to ignore the dead time correction on the data, just set this descriptor value to 0, or delete the descriptor itself.

  
Table C.6: EXSAS Special Header for images (filetype IMA)