Reading and Folding ASM Data II

Reading and Folding the ASM Database Over Lunch

The basic commands that are run are the following.

• Read the ASM data, requiring an ASM solution with chi^2 of less than 1.3 (this is probably too high for very faint sources, and too low for a bright source such as Sco X-1), using Modified Julian Date for the time value:

       ev = sitar_readasm(file,,,1.3,,1);
  

• Rebin the lightcurve into 7 day bins, requiring at least 7 data points per bin, and ignoring any bins with fewer data points:

       rb = sitar_rebin_rate(ev.time,ev.rate,,7.,,,7,1);
  

• Epoch fold with 500 logarithmic periods (folded into 20 phase bins) from 5 minutes to 500 days:

       ef = sitar_epfold_rate(ev.time,ev.rate,0.0037,500.,20,-500.);
  

To run this code, download the list of ASM data files (with trailing .lc stripped off): asm_files. Go to the All Sky Monitor web page and download all the data files. Note: You might have to modify the contents of asm_files, since the files available from the ASM page can change as sources are added or deleted. Finally, download the appropriate driver and example scripts from the SITAR downloads page, and save them as fold_the_asm.sl and fold_the_asm_examp.sl. In ISIS or Sherpa type: > () = evalfile("fold_the_asm"); An hour later, give or take, you will have three postscript plots (rebinned lightcurve, linear and log x-axis epoch folds) for the entire ASM catalogue. (The actual epoch fold data values can be saved by modifying the driver script to write out the arrays.)

One of course can custom modify the script. I have run the script using 10,000 logarithmically spaced periods, instead of just 500. This took about 21 CPU hours. Selected highlights presented below.

The 30 day super-orbital period of the low mass X-ray binary and X-ray pulsar, LMC X-4:

The 180 day super-orbital period of the low mass X-ray binary, X1820-303:

The 8.965 day orbital period of the high mass X-ray binary and X-ray pulsar, Vela X-1:

The following was generated by modifying the driver script used to fold the ASM lightcurve of Her X-1. Noting the extremely sharp peaks in the epoch fold results for Vela X-1 above, we have folded the Vela X-1 lightcurve on the fundamental 8.965 day period. The results are presented below, using 100 phase bins: