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Some help with a X-Ray astronomy question please!

  1. Nov 27, 2009 #1
    I've got to solve this problem and I am having quite an hard time figuring out how... Sorry, but I think I need help:

    "An astronomer takes a spectrum of a distant quasar using a 4m telescope. With an exposure
    time of one hour, the optical spectrum contains about 10,000 photons. The source emits 1/10
    as much power in the X-ray band as it emits in the optical band. The astronomer manages to
    get a 30 kilosecond observation with an X-ray observatory that has an e ffective area of 1000
    Assuming that the effciency of the telescope and spectrograph combination is 30%, how
    many photons will the resulting X-ray spectrum contain?"

    As far as I understand, What I should do here is
    1) to compare the two telescopes as if they had the same area and the same exposure time, so that I can infer how many optical photons the optical telescope would have gathered if it had the area and the exposure time of the X-Ray one.
    2) Then, I would take 1/10th of this result (the source is emitting 1/10 of Xray photons as compared to the optical ones) which will tell me the theoretical number of X-Ray photons the X-Ray telescope would have gathered with perfect efficiency.
    3) But knowing that the efficiency was only the 30%, I could have an estimate of the number of photons actually detected in the X-Ray spectrum.

    Problem is, I have no idea how to calculate step 1)

    Any suggestions?

    Thanks a lot.
  2. jcsd
  3. Nov 27, 2009 #2


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    Step 1 is just to calculate the number of photons/m^2/second on each telescope
    (Be careful with the units)
  4. Nov 28, 2009 #3
    You mean that if I calculate the photons per m^2 per second for the optical one whatever result I'll get the 1/10th of that number will be the photons per m^2 per second of the X-Ray one?
  5. Nov 28, 2009 #4


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  6. Nov 28, 2009 #5
    Guys, thanks a lot. Really appreciate. I'm happy to have discovered this forum, and I'll hopefully be able to actually help someone one day :)
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