Attitude Correction

After background subtraction, a data cube can be corrected for changes in the collimator response due to attitude variations. A two-dimensional response of the collimator has been derived from slew data of the Crab nebula (Kondo 1988; Turner et al. 1989). The collimator response function decreases by ~10 % every 0.1° and 0.2° increase in the X- and Z-directions respectively (see figure 13 in Turner et al. 1989). The program attcorr applies the attitude corrections to either data cubes or time series (the collimator response data is stored in the file $XACAL/trans.dat). However, the inner surfaces of the collimators were found to be reflective in the X-direction, amounting to a few percent below ~6 keV for an offset of ~0.3° from the collimator axis (Turner et al. 1989). Unfortunately, it is not possible to correct for this, as such a procedure requires precise knowledge of the satellite pointing direction, which is not available. The program attcorr works as follows:

qcl>attcorr

** ATTCORR Version 1.7 Fri Aug  8 20:48:41 1997 **
 
ATT_DATIN Input data filename =mkn335_91a.sub  
ATT_DATOUT Output data filename = mkn335_91a.sub_corr =
ATT_TR_FILE File containing transmission efficiency data =
$XACAL/trans.dat =
 
   DATIN  mkn335_91a.sub
                  
 
      Shape :    393 x    48 x     2   =  37728
              TIME    PHA     IDENT   
 
   IDENT masks
       1  0101010101010101
       2  1010101010101010
 
ATT_DO_REF Correct for collimator reflection (Y/N) = No =

Correcting MPC1/2 data cube.

ATTCORR Complete
qcl>

Attitude corrections work properly only on data cubes and time series so a background subtracted data cube should be corrected prior to the extraction of a spectrum.