RXTE Helpdesk/FAQ RXTE What's New HEASARC Site Map


RXTE
GOF
Working with the ASM Data Products
Recipes from the RXTE Cook Book
RXTE
FAQ

For the latest ASM weather map results results,
visit the RXTE ASM X-ray Weather Map

For the latest results for a particular source
visit the ASM Source Catalog

For the latest calibration news on the FITS products
visit the ASM Events page

For usage notes on the ASM Products
visit the ASM Data Productspage



When you use ASM data products in a paper or talk, please include the phrase: "results provided by the ASM/RXTE teams at MIT and at the RXTE SOF and GOF at NASA's GSFC."

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 The Quicklook products cover only the previous two weeks, and are superceded by the Definitive products, which are updated approximately weekly.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.

For further details about how the ASM data are analyzed to produce the light curves, see The XTE All Sky Monitor Data Products which is available via anonymous FTP as the PostScript file asm_products_v140.ps.


Obtaining ASM Data Products

The ASM products are available in either FITS or ASCII format. The latest status of the products is given on the ASM Data Products page.

The FITS formatted files are accessible via anonymous FTP from this page in the following subdirectories of /xte/data/archive/ASMProducts.

Direct anonymous FTP access via legacy.gsfc.nasa.gov is also available. The FITS formatted files may also be obtained via W3Browse.

ASCII formatted files may be obtained from MIT's ASM Light Curves Overview page. Customized ASCII formatted files may be obtained from the FITS files by using fdump or fv.

In addition, the most recent data may be obtained in ASCII format from RXTE ASM X-ray Weather Map.


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.

  1. First, using fparkey modify the MJD reference value in ASM Light Curve file so that MJDREFF = 0.000696574074.

  2. 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.

  3. Use fparkey to change the TIME column time unit (TUNIT1) from days ("d") to seconds ("s").

  4. 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

  5. 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:legacy.gsfc.nasa.gov/xte/data/archive/OrbitEphem/FPorbit_Day0800
    ftp:legacy.gsfc.nasa.gov/xte/data/archive/OrbitEphem/FPorbit_Day0801
    ftp:legacy.gsfc.nasa.gov/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.

  6. 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.

  7. 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").

  8. 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.

  9. If you wish, convert the BARYTIME values back to mission days using fcalc to divide them by 86400.0.

  10. 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 
    ....
    


If you have a question about RXTE, please send email to one of our help desks.

This page is maintained by the RXTE GOF and was last modified on Thursday, 21-Sep-2006 13:44:45 EDT.