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How do we know that the 2 types of waves came 2 seconds apart? Didn't we have to hunt for the light source after the gravitational wave detection, which must ha

by car 8y ago

How do we know that the 2 types of waves came 2 seconds apart? Didn't we have to hunt for the light source after the gravitational wave detection, which must have taken some time? Or were there cameras already trained on this part of the sky? Edit: Ok, read the linked article, and the explanation is the detection of gamma radiation, which is part of the electromagnetic spectrum 1.7 seconds after the gravitational waves. Not sure which satellite sensor picked them up, but I assume gamma ray observatories are not as directional as light telescopes, since there isn't a huge background of gamma emissions.

InclinedPlane 8y ago
The instrument in question is the gamma ray burst monitor (GBM) on the Fermi gammay ray telescope. The GBM does provide some directional data but because it's an all-sky instrument it is fairly crude but not terrifically so, it's able to determine the direction of a signal to within several degrees.
foxyv 8y ago
I had a physics professor that ran a Gamma Ray observatory in a high altitude balloon. (He accidentally spotted a few nuclear powered satellites in the process!) The way it worked is that instead of having a lens/mirror and an aperture pointed at a specific part of the sky it had a cube of sensors. Based on which sensors are triggered you can determine direction because high energy Gamma rays cause a cascade of different radiation when they hit a target. (Compton Scattering I think...) The downside of this method is the angular resolution is super low. Some Gamma ray telescopes are directional like Swift, but yeah, these Gamma Ray Bursts can be detected by non-directional observatories.
- car 8y ago
  Thank you, very interesting. Were those nuclear satellites known ones, as in this article: https://www.businessinsider.com/nuclear-powered-satellites-space-2016-3 https://www.businessinsider.com/nuclear-powered-satellites-s...? And were the Gamma ray sensors behind a collimator (basically lead plates with through-holes that only allow a very narrow angle of rays to be detected, e.g. used in Gamma cameras for nuclear medicine). Or were they in a 3D arrangement, and the timing of detection gave the direction? You said cube, so I assume it's the latter, but wanted to be sure.
  - foxyv 8y ago
    He didn't mention which satellites they were, I think he was under the impression they were Russian military satellites. Unfortunately this was all during my lower division courses so I didn't get a chance to work with him. When I was doing my senior project with a different professor we used different types of detectors for gamma ray spectroscopy. The two we had were these little sodium iodide detectors and a larger liquid nitrogen cooled gallium arsenide based detector. Pretty much just chunks of metal or salt that caused Compton scattering and were detected by photon multipliers or single photon counting modules. They often had multiple channels and were not very sensitive. It's been six years so my memory is kinda fuzzy. >_<

by car 8y ago

InclinedPlane 8y ago

The instrument in question is the gamma ray burst monitor (GBM) on the Fermi gammay ray telescope. The GBM does provide some directional data but because it's an all-sky instrument it is fairly crude but not terrifically so, it's able to determine the direction of a signal to within several degrees.

foxyv 8y ago

I had a physics professor that ran a Gamma Ray observatory in a high altitude balloon. (He accidentally spotted a few nuclear powered satellites in the process!) The way it worked is that instead of having a lens/mirror and an aperture pointed at a specific part of the sky it had a cube of sensors. Based on which sensors are triggered you can determine direction because high energy Gamma rays cause a cascade of different radiation when they hit a target. (Compton Scattering I think...) The downside of this method is the angular resolution is super low. Some Gamma ray telescopes are directional like Swift, but yeah, these Gamma Ray Bursts can be detected by non-directional observatories.

car 8y ago
Thank you, very interesting. Were those nuclear satellites known ones, as in this article: https://www.businessinsider.com/nuclear-powered-satellites-space-2016-3 https://www.businessinsider.com/nuclear-powered-satellites-s...? And were the Gamma ray sensors behind a collimator (basically lead plates with through-holes that only allow a very narrow angle of rays to be detected, e.g. used in Gamma cameras for nuclear medicine). Or were they in a 3D arrangement, and the timing of detection gave the direction? You said cube, so I assume it's the latter, but wanted to be sure.
- foxyv 8y ago
  He didn't mention which satellites they were, I think he was under the impression they were Russian military satellites. Unfortunately this was all during my lower division courses so I didn't get a chance to work with him. When I was doing my senior project with a different professor we used different types of detectors for gamma ray spectroscopy. The two we had were these little sodium iodide detectors and a larger liquid nitrogen cooled gallium arsenide based detector. Pretty much just chunks of metal or salt that caused Compton scattering and were detected by photon multipliers or single photon counting modules. They often had multiple channels and were not very sensitive. It's been six years so my memory is kinda fuzzy. >_<