Temporal analysis
Exploratory and interactive examination of variability of sources or background
is easily done within IDL's Event Browser:
idl
eb
Select Input File (choose event file)
Event Browser Manager:
Select Detector, Gratings and Grades as desired, then click Apply Filters
Click Positions, Image which brings up the field under a Bivariate Analysis window
Select the region of interest with the red markers (left and right mouse buttons),
click Use Markers and ROI: Filter. Adjust markers as desired.
Click Apply Filters
Click Light Curve which appears in a Univariate Analysis window
Adjust axes with axis buttons as desired.
Click Edit to change bin size, smooth, annotate, etc.
Click File to print or save the current light curve
Click Analysis to define and fit a model. To establish the probabillity that any
significant variations are present, we recommend displaying the Distribution
Function (do not smooth first), adopting a linear model (default), and using the
probability reported from the Kolmogorov-Smirnov one-sample test. Unless gaps are
present in the dataset, this should be a reliable test for variability.
WARNING! The "light curve" produced by EB is
a simple histogram of the event timestamps. GTI tables are NOT considered; thus
dropped CCD frames (from telemetry saturation) will corrupt the plot.
WARNING! EB does NOT know anything about the intrinsic
frame time of the data. If you choose (or let EB choose) a histogram bin size
that is not >> the CCD frame time you will get serious aliasing effects.
--- ooo ---
Programs from Arnold Rots at the CXC for barycentric correction
are available from D. Sanwal at ~divas/Barycor. The procedures are complex -- read the README
file in advance. The ephemeris used by CXC is DE405 with the ICRS coordinate system; this
should be satisfactory unless microsecond accuracy is needed.
-
Set an environment variable TIMING_DIR pointing to the EPHEM directory
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The principal program is axBary. It reads the orbital and input FITS event
lists and creates an output event file with timings changed to the barycentric
times. It also updates the headers etc. in the output file. However, the program
current fails to do the timing conversion for the GTI (good time intervals)
block, giving an error like "data not found for MJD 0.00". this may
affect later filtering of the data with GTIs.
axBary -i orbitFile -f inputDataFile -o outFile [-ra RA] [-dec DEC] [-ref refFrame]
CIAO has a tool lightcurve, which can also be run from the CIAO tool
FirstLook.
CXC has a number of caveats
about ACIS timing data which should be examined.