XMM-Newton Science Analysis System


epexposure (epexposure-0.16) [xmmsas_20230412_1735-21.0.0]

Algorithm

   subroutine epexposure
   
    Read all parameters	
    Open input event list(s) and auxiliary file from single exposure
    
    * call evlistcomb 
    in addition to epn default also propagate the FRAME column
    (this is needed to link the event list with CYCLE counters in the AUX file)
    
    * call evselect
    to create CCD specific filtered versions of the AUX file
    
    * call make_epexposure
    to actually perform the livetime computation

   end subroutine  epexposure

------------------------------   

   subroutine make_epexposure

    Read all parameters (passed on from epexposure)
    Open merged events file
    Open filtered(=CCD specific) auxiliary file
    Open housekeeping file

    Open frames output file and fill the primary header
    Create frames table extension (one per CCD)
    (this is temporarily used to collect counter info
     and to store livetime factors per frame)

    Create and fill columns:
    FRAME
    TIME: computed via call OAL_frameCounterToObt(aux1frameCol,obttags)
                       call OAL_obtToTimeTag(obttags,timetags) 
          for all frames which have an entry in the auxiliary file	
          compute time tags for all remaining frames from time steps

    Extract chopper value of quadrant under consideration: An_CHOP
      from housekeeping file, error if An_CHOP not constant, 
      store An_CHOP as attribute

    Extract number of cycles after which count info is sent: An_MAXFRC
      from housekeeping file, error if An_MAXFRC not constant

    NDISCLIN: extracted from auxiliary file, valid for An_MAXFRC frames

    Extract number of active CCDs in quadrant under consideration: An_CCDSEL	 
      from housekeeping file, error if An_CCDSEL not constant

    FC1: MIP dependent quadrant livetime factor
         (based on NDISCLIN, An_MAXFRC and An_CCDSEL)

    NEPDH: extracted from auxiliary file, valid for An_MAXFRC frames

    NEVENTS: computed number of raw events per frame from merged event list

    FC2: MIP dependent CCD livetime factor
         (based on EXPOSURE extension prepared by `epframes')

    flag all frames as bad where NEPDH /= NEVENTS
    (if ground MIP correction is active, NEPDH has to be reduced by rejected
    counts)

    Modify CCD specific EXPOSURE extension: add enough FRAME entries
      to store changing livetime factors

    Compute FRACEXP entries: epframes took care of FC0, now
      additional multiplication with FC1 and FC2 

    Compute livetime corrected exposure time and store it as attribute 

   end subroutine  make_epexposure