These forms allow you to extract an ASCII version of the ASM light curve for a desired source. You can then save this output as text for plotting or analysis. The data will be drawn directly from the most recent MIT weekly production data files. These files contain data points that have passed through our reliability filter criteria, as explained on the MIT ASM Light Curves Page.

The ascii-formatted data available here are provided primarily for convenience. While MIT and the GOF hope our instructions and information are adequate for most users, we are not prepared formally to support users of these data. We do, however, appreciate feedback.

Note that the RXTE SOF at NASA's GSFC has a script very similar to this, which allows you more flexibility in choosing your own filters, but it is most likely slower.

We ask that when results from these analyses are used, they be referenced as "quick-look results provided by the ASM/RXTE team." This team includes all those working on the ASM at MIT and at the Goddard Space Flight Center SOF and GOF.

For more information, please see the MIT ASM Light Curves Page.

Data Type

The ASM light curves are preserved in two default data types: the Dwell by Dwell files contain information pertaining to each individual 90-s observation of the source of interest. We also maintain files with One-Day Averaged intensities. Hardness ratios are also preserved at one-day intervals.

Each raw data point represents the fitted source flux from one 90 second dwell. The data files contain results from all three Scanning Shadow Cameras, and are quoted as rates in ASM counts per second, where the Crab nebula flux is about 75 ASM c/s (when at the center of an SSC field of view, with 8 anodes operational) in the 2-10 keV band. The ASM data are also preserved in three sub-bands . See table below for the normalized count rates for the Crab in each energy band.

Each "one-day average" data point represents the one-day average of the fitted source fluxes from a number (typically 5-10) of individual ASM dwells. The error value used in plotting the one-day averages is the quadrature average of the estimated errors on the individual dwells from that day (note that for sources expected to show little flux variation on shorter time scales, the RMS of the individual flux measurements -- fourth column of the data files -- may provide a better measure).

Start and Stop Times

The ASM light curves are given as a function of time in Modified Julian Date (MJD). If you know the MJD values of the time interval you require, you may enter them directly in the fields for the MJD. If not, you may select the Year, Month, and Day, and the web page will display the corresponding MJD automatically.

Notes on Columns

The "Data by Dwell" ASCII files contain the following columns:

  1. MJD of the observation (JD - 2,400,000.5)
  2. SSC unit number
  3. Dwell sequence number
  4. Dwell number
  5. Reduced chi-square of the fit
  6. Number of sources in the field of view
  7. Earth angle (degrees)
  8. Fitted ASM unit count rate (counts/second; Crab is ~75)
  9. Estimated error (counts/second)
  10. Exposure time (seconds)
  11. Long-axis angle theta (degrees)
  12. Short-axis angle phi (degrees)
The count rate and estimated error are available in all four energy bands.

The "One-Day Averages" ASCII data files contain five columns:

  1. MJD of the observation (JD - 2,400,000.5)
  2. Averaged ASM unit count rate for the day (counts/second; Crab is ~75)
  3. RMS estimated error (counts/second)
  4. RMS deviation of the points from the one-day mean (counts/second)
  5. Number of dwells averaged
The count rate, RMS error, and RMS scatter are available in all four energy bands. There are also two hardness ratios with associated errors. The hardness ratio 1 is the ratio between the counts in the B band to the counts in the A band, and the hardness ratio 2 is the ratio of the counts in the C band to the counts in the B band. The ASM energy channels span the following nominal energy ranges (in keV):

BandEnergy RangeCrab ASM c/s
B3-5 23.3
C5-12 25.4

The output light curve will contain the columns you select in the same order as presented here.

Source Coordinates:

If you are not sure of the name of your desired source in the ASM catalog, you may enter the coordinates here (in either decimal or sexigesimal format), and we will choose the closest ASM source to that location. (Equinox J2000.0 only, please.)

Source Name:

You may know the source name in an alternate form to what we use in the ASM Catalog. We have a list of alternate names for ASM catalogued sources, and if you enter a source name, or a piece of a source name, we will try to find the ASM catalog name for you. (This form is not case sensitive, and spaces are ignored.)

This page and associated code written and maintained by Don Smith.