Subsections

• E..4.1 Actions
• E..4.2 Usage and Inputs
• E..4.3 Data Products

E..4 TIMING Stage

This stage is run for each observation to perform timing analyses, as shown in Figure 8.

BEWARE: none of AE's timing analysis (light curves, median energy time series, variability measures) currently takes the background into account! This can produce misleading results in some cases, e.g. a spurious indication of variability between two ObsIds that have very different backgrounds.

E..4.1 Actions

• A ``grouped'' light curve (i.e. a light curve with unequal bin sizes) is constructed. The median energy of events in each time bin is computed. Exposure in each time bin is computed using the appropriate GTI table.

• Errors on the light curve and median energy values are estimated.

• An adaptively smoothed light curve is computed.

• Time variability of the source within the specified observation is quantified by comparing a uniform count rate model to the distribution of source event time stamps and computing the 1-sample Kolmogorov-Smirnov statistic. The significance of the KS statistic is saved in the keyword PROB_KS in obs.stats; values near 0 suggest variability. The code accounts for gaps in the observation using the GTI tables.

E..4.2 Usage and Inputs

acis_extract, srclist_filename, obsname, /TIMING, ENERGY_RANGE=[energy,energy], SNR_RANGE=[value,value], NUM_GROUPS_RANGE=[value,value]

EXAMPLE:
idl $\vert\&$ tee timing_1875.log

acis_extract, 'all.srclist', '1875', /TIMING, ENERGY_RANGE=[0.5,8], SNR_RANGE=[2,20], NUM_GROUPS_RANGE=[2,100]

• The optional ENERGY_RANGE parameter defines the energy band over which the light curve is computed; default is [0.5,8.0].

• The optional keywords SNR_RANGE and NUM_GROUPS_RANGE change the time binning parameters. See §5.7 for the meaning of these parameters, each of which is a 2-element vector.

E..4.3 Data Products

For each source the following files are produced:

{sourcename}/{obsname}/source.lc:

a FITS table containing the grouped light curve, grouped median energy time-series, exposure time series, and adaptively smoothed light curve. The exposure values in this table attempt to account for both the integration time within each time bin (obtained from the GTI tables) and the ARF value (effective area and PSF fraction) associated with this ObsId. This facilitates testing for variability across ObsIds in the MERGE stage.

{sourcename}/{obsname}/source.evt.ps:

a PostScript file containing a scatter plot of event arrival times and energies, and a plot of the observed and uniform cumulative distribution functions used to compute KS probability.

To accommodate multiple observations, the binned and smoothed light curves are plotted in the MERGE_OBSERVATIONS stage.