XMM-Newton Science Analysis System


evarimgen (evarimgen-1.0.2) [xmmsas_20230412_1735-21.0.0]

Algorithm

read parameters;

if (sortevlist) {
  sort the event list;
} else {
  check that the events occur in time order, warn if not;
}

calculate the dimensions of the variability image;

if (withimage) {
  load fluxImage;
} else {
  make fluxImage;
  write fluxImage as a FITS file;
}

# Make the KSS image:
ksImage(1:max_i, 1:max_j) = 0.0;
counts( 1:max_i, 1:max_j) = 0;
for (event from 1 to n_events) {
  if (the event is within the image bounds) {
    calculate pixel (i,j) that this event falls into;
    counts(i, j) = counts(i, j) + 1;
    d = abs((event - 1) / n_events - counts(i, j) / fluxImage(i, j));
    if (ksImage(i, j) < d) {
      ksImage(i, j) = d;
    }
  }
}

# Weight the KSS image:
foreach (i) {
  foreach (j) {
    if (counts(i, j) > cutoff) {
      sqrtNe = sqrt(n_events * counts(i, j) / (n_events + counts(i, j)));
      ksImage(i, j) = ksImage(i, j) * (sqrtNe + 0.12 + 0.11 / sqrtNe);
    } else {
      ksImage(i, j) = 0.827574; # value at which prob of variability is 50%
    }
  }
}

write ksImage as a FITS file;