abc HEADAS help file

NAME

ABC - corrects the arrival times of the rosat photon at the barycenter.

USAGE

        abc infile bcfile outfile ra dec

DESCRIPTION

This task corrects the arrival times of the photons, in the EVENT extension and the times in the GTI extension, for the spacecraft clock to UTC relation (SCC-UTC) and uses the correction table created from the task BCT to correct the arrival time to the barycenter. The Barycenter correction is computed by a linear interpolation between the corrected orbit times (output from BCT). If a photon falls outside of the orbit interval a warning is issued together with the photon time.

This task takes as input:

1. A photon event list data file (in FITS) in either RDF/REV2 format or older US REV0 format (the German REV0 formatted data is not supported). To minimize the amount of time needed for ABC to run, we recommend that the event data be spatially screened so that it only contains photons from the source for which the correction is required.

2. A correction table. This table, created by the task 'BCT', contains the corrected and uncorrected orbit times. The table is in FITS format. It consists of 4 columns, containing the integer and the fractional part of the uncorrected and corrected times. The times are written as JD. See also help on BCT.

3.the equatorial coordinates of the source (epoch 2000.0) given either as hh mm ss.s, dd mm ss.s (separated by a blank space) or in degrees. The coordinates are not used for computation but they are requested in order to test the compatability with the input correction table (from 'BCT').

This task generates:

1. An output event file with the arrival times of the photon corrected at the barycenter.

Correction of photon times to UTC:

The ROSAT spacecraft clock was calibrated to UTC by dividing the ROSAT mission into 10 time intervals and fitting the SCC - UTC relation with a fifth order polynomial. The start and stop times of the intervals, and the fit coefficients, are stored in a file called scc_to_utc2.fits, available either from the REFDATA area ($LHEASOFT/../refdata) For each photon, the correction of the spacecraft clock times (SCC) to UTC is computed according to the following formula :

     UTC =  JDref(I) + (A(i,1)/86400.0 
                     + (A(i,2)*(SCC-SCCo(i))/86400.0
                     + (A(i,3)*(SCC-SCCo(i))**2/86400.0
                     + (A(i,4)*(SCC-SCCo(i))**3/86400.0
                     + (A(i,5)*(SCC-SCCo(i))**4/86400.0

where

     i= the appropriate mission interval containing the SCC time of arrival for 
     that photon
     A(i,j)= the coefficient of the jth polynomial in the ith time interval
     SCCo = an offset time for the ith interval
     JDRef(i) = an offset time for the ith interval

PARAMETERS

infile [filename]: Input event file name. The ABC task accepts RDF/REV2 formatted events file (i.e. the formats available from the ROSAT archive) or old-style US/REV0 formats (originally distributed to US PI's). German REV0 formatted data is not supported but may be converted to a supported format using the tool gevt2rdf.
bcfile [filename]: The name of the FITS file containing the correction table generated as output from the task BCT. BCFILE should contain 4 columns, respectively the integer and the fractional part of the uncorrected and corrected times for the orbit data. The times are written as JD.
outfile [filename]: Name of the output file for the event file produced by ABC, containing the corrected times. Note that the correction is applied to the extension containing the photon events AND the extension containing the good time intervals.
ra [string]: The r.a. of the source given either in hh mm ss.s or deg (equinox 2000).
dec [string]: The dec. of the source given either in dd mm ss.s or deg (equinox 2000.0).
(tchat = 10) [integer]: Terminal chattiness level. Higher means more chattiness.
(lchat = 0) [integer]: Log file chattiness level. Enable logging by setting FLOGFILE environment variable to filename. Prefix a + to append to an existing file.
(sccfile = scc_to_utc2.tfits) [filename]: Name of the SCC correction table, which is normally included in the HEASOFT REFDATA area

EXAMPLES

     % bct
     Name of input file [orbit file][] rp900176a01_anc.fits
     Name of output file[] bct.out
     RA in hh mm ss.s or degrees -- epoch 2000[] 10 45 13
     DEC in dd mm ss.s or degrees -- epoch 2000[] -59 44 20
     WARNING:  Defaulting to first FITS extension
      
      Extensions:
      
               HDU type     HDU name               Rows  Columns
     ____________________________________________________________
        2  Binary Table      EPHEM                  422     19
     
     
     % abc
     Name of input events file[] rp900176a01_bas.fits
     Name of barycenter correction table[] bct.out
     Name of output file[] abc.out
     RA in hh mm ss.s or degrees -- epoch 2000[] 10 45 13
     DEC in dd mm ss.s or degrees -- epoch 2000[] -59 44 20
     Copying to output file...
     ...done
      
      Extensions:
      
               HDU type     HDU name               Rows  Columns
     ____________________________________________________________
        2  Binary Table      STDEVT              283394      8
        1  Binary Table      STDGTI                  17      3
      
      
      Extensions:
      
               HDU type     HDU name               Rows  Columns
     ____________________________________________________________
        1  Binary Table      TIMEREF                422      4

BUGS

For LHEASOFT version 5.1 and earlier, this tool will fail if the input photon events file is compressed.