# Some help with a X-Ray astronomy question please

• Maitreya
In summary, the 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 effective area of 1000 cm2. Assuming that the effciency of the telescope and spectrograph combination is 30%, how many photons will the resulting X-ray spectrum contain?
Maitreya
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
cm2.
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.

Step 1 is just to calculate the number of photons/m^2/second on each telescope
(Be careful with the units)

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?

Yes.

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 :)

## 1. What is X-Ray astronomy?

X-Ray astronomy is a branch of astronomy that studies objects in the universe by detecting and analyzing the X-rays they emit. X-rays are a form of electromagnetic radiation with high energy and short wavelengths, and they are produced by extremely hot and energetic objects such as black holes, neutron stars, and supernova remnants.

## 2. How do X-rays help us understand the universe?

X-rays provide valuable information about the composition, temperature, and motion of objects in the universe that cannot be observed through visible light. This allows us to study extreme objects and phenomena, such as black holes and supernovas, and gain a better understanding of the physical processes that govern the universe.

## 3. What is the difference between X-ray astronomy and other forms of astronomy?

The main difference between X-ray astronomy and other forms of astronomy, such as visible light or infrared astronomy, is the type of radiation that is being studied. X-ray astronomy focuses on the detection and analysis of X-rays, while other forms of astronomy study different wavelengths of electromagnetic radiation. Each form of astronomy provides unique insights into the universe.

## 4. What are some common tools and techniques used in X-ray astronomy?

X-ray telescopes, such as the Chandra X-ray Observatory and the XMM-Newton spacecraft, are the primary tools used in X-ray astronomy. These telescopes use special mirrors and detectors to collect and analyze X-rays from space. X-ray spectroscopy, imaging, and timing are some of the techniques used to study X-rays from celestial objects.

## 5. What are some current research topics in X-ray astronomy?

Some current research topics in X-ray astronomy include the study of black holes and their effect on their surrounding environments, the formation of galaxy clusters and groups, and the detection of hot gas in galaxy clusters. Other topics include the search for dark matter, the study of supernova explosions, and the investigation of X-ray emission from neutron stars and white dwarfs.

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