ASM Light Curve files
Plotting Lightcurves
ASM light curve files can be plotted readily using fplot, with TIME
as the x-axis, RATE as the y-axis, and ERROR as the uncertainties on
the intensities. Note that since independent
solutions for each SSC are included in the file, there may exist
more than one intensity value at a given time. fplot will plot the
intensity from each 90 s dwell without any rebinning.
The light curve files may also be used in the Xronos ftools. However,
because the Xronos ftools use Truncated Julian Days (TJD = JD -
2440000.5) whereas XTE times are given in Modified Julian Days (MJD =
JD - 2400000.5) the first digit of the MJD reference date in the light
curve file is truncated. This causes the values on the time axis to be
misleading. This can overcome by using the stX option to shift the times.
As an example of plotting an ASM light curve file using the Xronos
ftool lcurve:
> lcurve tunit=3
lcurve 1.0 (xronos5.1)
Number of time series for this task[1]
Ser. 1 filename +options (or @file of filenames +options)[]
xa_gx1+4_d1.lc st-9353
....
Using tunit=3 forces the time axis on the plot to be in days. Using
st-9353 reckons the time axis to XTE Mission Days, which start on Jan 1, 1994.
lcurve will compute an unweighted average of any data binned
together. Note that because of the uneven sampling inherent in the
ASM light curves, using the negative binning option (e.g. -1) to bin in
multiples of the data's inherent binning will not work. If you wish a
plot of the unbinned data points, use fplot.
Computing Power Spectra
Because the sampling for any particular source is uneven, you may find
it difficult to compute the power spectrum using powspec, which
rejects intervals if many bins are empty. One way
to get around this is to use xronwin to change the exposure criterion
for the interval from its default value of 50 % to something smaller.
> xronwin
[T] Change TIME Windows
[P] Change PHASE Windows
[F] Change FLUX Windows
[E] Change EXPOSURE Windows
[R] READ an Input file
[S] SHOW All Defined Windows
[C] CLEAR All Defined Windows
[W] WRITE Window file
[Q] QUIT Window Program
[DS] Define Series Number (Currently 1)
[DB] Define Bin Type (Currently Orig. Bins)
[DE] Define Epoch for Phase Windows (Currently Undefined)
[DP] Define Period for Phase Windows (Currently Undefined)
[DW] Copy Defined Windows from Series to Series
First, change the bin type to Interval:
Choose an action: db
Current bin type is: Orig. Bins
[O] original bin windows
[N] new bin windows
[I] interval windows
Bin type ( to main menu): i
Current bin type is: Intervals
[O] original bin windows
[N] new bin windows
[I] interval windows
Bin type ( to main menu): <CR>
Now redefine the interval exposure criterion:
Choose an action: e
Current Exposure Window for series 1, Intervals is:
0.00 50.0
[#] Minimum exposure
[-] Delete this window
<RETURN> to main menu.
Action: 0.0
Input maximum exposure: 25.0
Current Exposure Window for series 1, Intervals is:
0.0 25.0
[#] Minimum exposure
[-] Delete this window
<RETURN> to main menu.
Write the result to an output file:
Choose an action: w
What should I call your output window file: temp
Input the file temp.wi as the window file in powspec.
A preferred means of computing power spectra is to use perdgrm, which
uses a periodogram method and performs no binning on the light curve.
To speed up the processing,
you may specify a minimum period to search, instead of using the
default value of 0. The units for inminp is the same as the time unit
in the file, i.e. days for ASM files.
> perdgrm inminp=0.25
Name of FITS file and [ext#][testg.lc] xa_smcx1_d1.lc
Name of output FITS file[testg.ft] xa_smcx1_d1.ft
min & max time ranges for intervals to be analyzed[-]
RMS error of fit for subtracting polynomial[-5]
perdgrm3.6.1 : 866 Instances of duplicate times
>
perdgrm counts the number of instances it finds more than one data
point occuring at the same time. However, these data points are used
in computing the periodogram.
Creating Customized ASCII Files
Customized ASCII formatted files may be obtained
from the FITS files by using fdump or fv. Customarily you will
dump the TIME, RATE, and ERROR columns. Other potentially useful
columns include SSC_NUMBER (which identifies which SSC the intensity
was derived from) and RDCHI_SQ (which gives the reduced chi squared
for the fit).
ASM Color files
The ASM color files contain the data from each of three colors for
each SSC. The energy bands for the colors are 1.3-3.0 keV, 3.0-5.0
keV, and 5.0-12.1 keV.
The color files may be split into separate light curve files using
asmchannel:
> asmchannel
ASMCHANNEL V1.0
Input name of ASM color file:
xa_smcx1_d1.col
writing xa_smcx1_d1_ch1.lc
writing xa_smcx1_d1_ch2.lc
writing xa_smcx1_d1_ch3.lc
all done
>
The resulting three files may then be analyzed as light curve files (see
above), or may be input to lcurve to simultaneously plot
the three light curves or to create color-color diagrams.
Applying Barycenter Correction to ASM Light Curves
Using faxbary---an improved barycentering routine that the GOF
now recommends in favor of the older fxbary---
it is possible to apply a barycenter
correction to the ASM Light Curves. However, the user must first
make some modifications to the ASM light curve of interest.
- First, using fparkey modify the MJD reference value in ASM Light
Curve file so that MJDREFF = 0.000696574074.
- Convert the values of the TIME column from mission days to
mission elapsed seconds. You may do this Using fcalc to
multiply the TIME values by 86400.0.
- Use fparkey to change the TIME column time unit (TUNIT1) from days ("d") to seconds ("s").
- Change the value of the
TIERABSO keyword from the current (string) value to the numerical value
of
0.0 so that it looks like this:
TIERABSO= 0.0 / Absolute timing precision
- NOTE: faxbary runs quickly on long observations
due to a newly created single, mission-long orbit file
currently called (
FPorbit_0729_3431.fits
). The latest version can always
can be downloaded from the OrbitEphem directory in the XTE data archive.
It's large (about 218Mb).
Users concerned with the overhead
of downloading it can use the list of orbit files as described
in the next step;
in
that case each time you run faxbary the merging will happen on-the-fly.
If the mission-long orbit file in the OrbitEphem directory is out of
date
for a user's purposes, then individual orbit files can be appended by
using the orbit file list method below, taking the mission-long orbit
file as the first file, and then listing subsequent FP_orbit_DayXXXX
files
to be appended to it.
OR: If not using the mission-long orbit file described above,
create a text file containing a list of the names and locations of the
appropriate orbit ephemeris files.
Note that very little ASM data was
collected between mission days 740-782.)
The orbit files may be either downloaded or referred to directly
via their location in the archive, e.g.
ftp:heasarc.gsfc.nasa.gov/FTP/xte/data/archive/OrbitEphem/FPorbit_Day0800
ftp:heasarc.gsfc.nasa.gov/FTP/xte/data/archive/OrbitEphem/FPorbit_Day0801
ftp:heasarc.gsfc.nasa.gov/FTP/xte/data/archive/OrbitEphem/FPorbit_Day0802
etc.
NOTE: The limit of 1000 orbit files quoted for fxbary
does not
apply to faxbary. In fact, the quoted limit of 1000 files for
fxbary is incorrect due to a bug in the program. The actual
limit to number of orbit files is 100!
Conversely, the new mission-long orbit file cannot be used
with
fxbary.
If you are still using fxbary, and you
have more than 100 days of data, split the
ASM light curve into 100 day segments using fselect. Likewise,
create multiple text files with 100 or less orbit ephemeris files.
In each of the ASM light curve file(s), use
fparkey or fmodhead to modify the TSTART and TSTOP
values so that they lie within the TSTART of the first orbit file and
the TSTOP of the last orbit file. Note that these times must be in
Mission Elapsed Time (seconds). It is sufficient to modify only the
integer portions (TSTARTI and TSTOPI) of these keywords. Also change
the TIMEUNIT keyword from days ("d") to seconds ("s").
Run faxbary on the modified ASM light curve file(s). Note that
the barycentered time will be in a new column named BARYTIME in column
number 18.
If you wish, convert the BARYTIME values back to mission days
using fcalc to divide them by 86400.0.
Multiple light curve files may be read into the Xronos timing
tools using the @filename convention. Remember that the BARYTIME values
are in column 18. Hence to read in the barycentered times, use the vxN
option when giving the file name, e.g.
Ser. 1 filename +options (or @file of filenames +options)[]
xa_cygx1_bary_d1.lc st-9353 vx18
....
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