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       *                --- EXSAS --- Version  JANUARY 1996             * 
       ****************************************************************** 

                 
                       
 15-DEC-95  CREATE/SOURCE_DETECT_IMAGE: parameter [pet] now defaulted to 
            events.tbl. Parameter [ampl] has new default 1-256.               
            
                                                         (DOE - 3862/3340)   
  
 15-DEC-95  DETECT/SOURCES : parameter [ima] now defaulted to image1.bdf,     
            parameter [pem] now defaulted to events.tbl                       
                                                          (DOE - 3862/3340)   
  
 15-DEC-95  CREATE/BG_IMAGE, CREATE/SMOOTHED_BG, DETECT/MAP, MERGE/SOURCES,   
            DETECT/MAXLIK, COMPUTE/UPPER_LIMITS, DETECT/SOURCES:              
            All of the code dealing with background calculations has been     
            revised:                                                          
              o  all calculations done in REAL instead of INTEGER             
              o  CREATE/BG features automatic rebinning of the fitted map     
                 in case of low photon statistics. Increased accuracy. Runs   
                 also faster now.                                             
              o  capable of handling very low backgrounds (down to 0.00001    
                 cts/pixel).                                                  
              o  background scale factor now obsolete, defaulted to 1.        
              o  background countrate column in all source lists with 5       
                 significant decimals                                         
            If you want to use older background maps with a background scale  
            factor different from 1., check if descriptor BG_SCALE exists.    
            If it does exist, you can use them as before.                     
                                                          (DOE - 3862/3340)   
  
 23 Jan 1996 -  The command READ/RANGES is upgraded, now it works 
                with any Projection table and supply a complete description 
                of spatial selection applied to data. Read Help! 
                                                         (Izzo-3313) 
  
 29-JAN-96  PROCESS/HK : an updated solar activity file led to incorrect      
            column densities N_O, etc. This was caused by an array limit of   
            2000 in an initialization routine. This number has now been       
            changed to 4000 (which extends the validity beyond the year 2001) 
  
            Affected: column densities [N_O, N_O2, N_A, N_H, N_N, N_He] in    
            output table if called after 16-JAN-1996 16:49. All other table   
            columns were not influenced.                                      
  
            The command PROCESS/HK now also works if the eventsrates file is  
            missing, orbit and attitude data are still required. 
                                                          (MJF - 3849) 
  
 29-JAN-96  CREATE/NORTH_ALIGNED_IMAGE : works also for very small rotation   
            angles.                                      (AJV, DOE - 3343)    
  
 29-JAN-96  CREATE/EXPOSURE : useable again for non-centered reference images 
            (images where the image center does not coincide with sky pixel   
            coordinates 0,0 = nominal pointing direction).                    
                                                              (DOE - 3343)    
  
 30-JAN-96  FIT/SPECTRUM & MODEL/SPECTRUM :                                   
            An inconsitent definition of the number of model parameters in the 
            spectral models *tblm* and *tbef* has been corrected. The bug     
            resulted in warnings like "Unaligne access......" but did not " 
            affect the fitting results.                                    
                                                              (WEB - 3588)    
 07-Feb-96 New SCC to UTC calibration: Version 2_95                           
           The conversion of space craft clock times from SCC to UTC is now   
           based on clock calibration data up to 11-Dec-1995. Conversion      
           after this date is done by extrapolation. Plots showing the        
           residuals of the scc/utc polynomial fits for the years 1990 to 95  
           can be found in the ROSAT service area under (.../exsas/scc_utc).  
           Three new descriptors (Version, Validity & Producer) have been     
           introduced with this release for identification purposes.          
                                                                              
                                                              (WEB - 3588)    
  
 16-Feb-96 Some descriptors in the default detector response matrix files     
           have been changed. In the case of problems please contact me asap. 
                                                                              
                                                              (WEB - 3588)    
  
 27-Feb-96 FIT/SPECTRUM & MODEL/SPECTRUM :                                    
           The maximum number of grid steps has been changed from 50 to 100.  
                                                                              
                                                              (WEB - 3588)    
  
 15-MAR-96 INTEGRATE/FLUX:                                                    
           Checks now if the integrated flux was computed taking the galactic 
           absorption model GAMM() into account. If the integrated flux is the 
           absorbed flux a note is given on the screen.                       
                                                              (WEB - 3588)    
  
 19-MAR-96 EXSAS'96 for LINUX.ELF                                              
           =======================                                             
           A new version of EXSAS'96 for Linux (Kernel version 1.2.13 - ELF)   
           optimised for INTEL Pentium and i486 CPU's is available from the    
           the ROSAT service area (/info_svc/rosat_svc/exsas/96JAN_EXP_Linux). 
           The disk space required to install MIDAS (release 95NOV) and EXSAS  
           is about 100 MB. MIDAS (95NOV) for LINUX.ELF is available from ESO  
           and /info_svc/rosat_svc/exsas/96JAN_EXP_Linux/95NOVpl2_MIDAS. To    
           support a fast and easy installation of the new software releases   
           1.44 MB floppys with EXSAS'96 and a MIDAS CD-ROM are available on   
           request.                                                            
                                                               (WEB - 3588)    
  
 20-Mar-96 New version of IDENTIFY/SOURCE available. Enhanced functionality,
           see on line help. 
                                                   (H.U.Zimmermann - 3593) 
  
 21-MAR-96 INTEGRATE/FLUX:                                                     
           The source code has been revised and optimized for the special 
           task of flux integration. In the case of problems please contact 
           me asap.     
                                                               (WEB - 3588)    
  
 15-APR-96 NEW Command: PLOT/PULSE_PROFILE:                                    
           Produces a fancy plot of the bined pulse profile deduced by a       
           photon arrival time analysis using Make/Folding. See the help       
           file for a more detailed description of the calling syntax.         
                                                                               
                                                               (WEB - 3588)    
  
 25-APR-96 CREATE/EXPOSURE_MAP: bug fixed.                                     
           The deadtime correction is now applied correctly. Since the default 
           is  no deadtime correction , most exposure maps produced earlier    
           should not have been affected.                      
                                                               (DOE - 3343)    
  
 30-APR-96 DETECT/MAXLIK, COMPUTE/UPPER                                        
           Now rows in the merged input source list mplst.tbl can be sorted,   
           edited, or selected in any way before running source detection.     
           Until now it was possible that part of the sources in such modified 
           merged source lists were skipped, and not fitted.   
                                                               (DOE - 3343)    
  
 20-JUN-96 CALCULATE/GALACTIC_NH (!!!)                                         
           The unit of the output has been changed from 10^20 1/cm^2 to        
           10^21 1/cm^21 to reach agreement with the units of Nh used in the   
           parameter files of the spectral fiting procedures.   
                                                               (WEB - 3588)    

 24-JUN-96 New Command: =>  CONVERT/CTS2FLX  <=                                
           The program computes the energy flux for a given count rate and     
           spectral model. See the online help for a detailed description of   
           the command syntax. Additional background information on how the    
           command works can be found on the EXSAS Spectral Analysis Homepage. 
           See:  http://www.rosat.mpe-garching.mpg.de/~web/exsas.html 
  
                                                               (WEB - 3588)    

 03-JUL-96 CONVERT/CTS2FLX has been renamed to CONVERT/RATE_TO_FLUX            
                                                                               
                                                               (WEB - 3588)    
  
 09-JUL-96 CORRECT/BARYCENTER                                                  
           The Julian days of the leap seconds which were used to compute the  
           number of leap seconds since 1972 have refered to 12h rather than   
           to 0h, the actual time the leap second was introduced. This         
           results in errors for pulse arrival time measurements if the pulsar 
           observation was performed at that day where the leap second was     
           applied. The leap second reference times are now correct.           
  
                                                               (WEB - 3588)    
    
 27-AUG-96 PROCESS/HK                                                          
           The solar and geomagnetic activity file has been updated. The data  
           are neccessary for the atmospheric calculations. The validity range 
           is now from launch till 31-JUL-1996.                                
                                                               (MJF - 3849)    
  
 05-SEP-96 INTEGRATE/RING                                                      
           Works now also for shrunken images.                                 
           ( LOAD/IMAGE image scale=negative value )      (DOE - 3343)    
  
  
 09-SEP-96 DETECT/LOCAL does not produce sources with background < 0 anymore.  

                                                               (DOE - 3343)    
  
 17-SEP-96 CORRECT/BARYCENTER                                                  
           is now using the first and last photon event time of the given    
           table to check for consistency with the orbit file. Before only the 
           first and last entry of the TIM_SEL descriptor was used. This has  
           caused trouble for low count rate objects and prompted the warning: 
           *Correction table and photon table not compatible. Check the times* 
           although the orbit file actually covered all photon arrival times   
           of the given table.                                                 
                                                               (WEB - 3588)    

  
 27-SEP-96 Now MERGE/FILES handles also raw events tables - see help 
       
                                                               (IZZO - 3313) 
  
 09-OCT-96 PROCESS/CT                                                          
           This new command is designed for REV2 processed PSPC data. Starting 
           from raw event tables you can choose a different gain in addition   
           to all other corrections that are applied by the SASS CT module.    
           On-line help is available.                                          
                                                               (MJF - 3849)    
  
 10-OCT-96 The new command EXTRACT/ACCEPTED_TIMES is available. It reads the   
           TIM_SEL descriptor and creates an output table with start and end   
           times of accepted intervals. On-line help is available.             
  
                                                               (MJF - 3849)    
 15-OCT-96 New SCC to UTC calibration: Version 1_96                           
           The conversion of space craft clock times from SCC to UTC is now   
           based on clock calibration data up to 02-Sep-1996. Conversion      
           after this date is done by extrapolation. Plots showing the        
           residuals of the scc/utc polynomial fits for the years 1990 to 96  
           can be found in the ROSAT calibration area or through my homepage  
           http://www.rosat.mpe-garching.mpg.de/~web/exsas_hp/exsas.html.     
                                                                              
                                                              (WEB - 3588)