Getting the spectrum

We'll start with GX5-1.  There are going to be two ways to get this spectrum.  Method 1 is to look for observations done close to mine (which was done Feb 10, 2007).  And it turns out there is one, a long observation done with the Chandra High Energy Transmission Grating (HETG) on Oct 30, 2006.  The  beauty of this observation is that it will measure an extremely accurate spectrum for the source.  However, X-ray binaries like GX5-1 tend to jump up and down in both brightness and spectrum on time periods even less than a day.  So, while this observation isn't useless to me, I could really use something on the same day.

For this, I'll use observations from the All-sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE).  Although this detector only measures in 3 energy bands, it does so all the time for a large number of sources, including GX5-1 and GX9+1.  So I can look each one up and see what each source was doing.  For GX5-1, the light curve of all 3 bands added together shows that there's a certain amount of variation, but it doesn't go nuts.  In fact, what's really useful is to look at a histogram of the count rates, to see just how much variation there is. 

What I get from this is that the average flux is ~65 RXTE ASM counts per second, and that on the day of my observation, the flux was pretty much average.  Helpfully, on the day of the HETG observation, it was also pretty average.  I also looked at the ratio of the bands individually, and confirmed that they didn't have a lot of variation on this timescale either.  So, although GX5-1 can vary at lot, it didn't choose to during this time period.  Quite helpful of it.

This means I can move on to analyzing the HETG spectrum and use that as a proxy for the spectrum during my observation.