Introduction

The RXTE ASM Data Products consist of light curves and color files in FITS format for each of the ~ 350 sources in the ASM catalogue. These files can be analyzed using the ftools, or they may be converted to ascii files for analysis by the user's own tools. Light curves and color files are collected for both the Quicklook results derived from the real-time data collected in the SOF, and for the Definitive results obtained through analysis of the processed data by the RXTE ASM team at MIT. The Quicklook products cover only the previous two weeks, and are superceded by the Definitive products, which are updated approximately weekly.

An important feature of the light curves and color files is that because two of the ASM Scanning Shadow Cameras (SSCs) have overlapping fields of view and because data from each camera are analyzed independently, it is often the case that sources may have multiple intensity measurements at the same time. These measurements are, however, independent and may be combined as such.

Obtaining ASM Data Products

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

   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> 

   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.

   Choose an action: w
   What should I call your output window file: temp

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

   > 

Creating Customized ASCII Files

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
   >	

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.