APOD: Gamma-ray Rain from 3C 279 (2015 Jul 22)

Comments and questions about the APOD on the main view screen.
User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gamma-ray Rain from 3C 279 (2015 Jul 22)

Post by neufer » Thu Jul 23, 2015 2:22 am

dbooksta wrote:
If I'm reading the description correctly and looking at the aggregated signals: This galaxy 5 billion light years away has a burst that spans about half a degree? The same as the sun and moon? How can that possibly be right?
  • Probably just the resolution of the telescope:
https://en.wikipedia.org/wiki/Fermi_Gamma-ray_Space_Telescope wrote:
<<The Fermi Gamma-ray Space Telescope's Large Area Telescope (LAT) imaging gamma-ray detector (a pair-conversion instrument) detects photons with energy from about 20 MeV to 300 GeV.

The resolution of its images is a few arc minutes for the highest-energy photons [but only about] 3 degrees at 100 MeV.>>
Art Neuendorffer

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18805
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gamma-ray Rain from 3C 279 (2015 Jul 22)

Post by neufer » Thu Jul 23, 2015 2:28 am

Norm wrote:
My question regards the time lapse that this video represents.
Did it happen in days, hours, minutes ?
http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11947 wrote:
<<The movie starts on June 14 and ends June 17.>>
Art Neuendorffer

User avatar
alter-ego
Serendipitous Sleuthhound
Posts: 1121
Joined: Mon Apr 21, 2008 4:51 am
Location: Redmond, WA

Re: APOD: Gamma-ray Rain from 3C 279 (2015 Jul 22)

Post by alter-ego » Thu Jul 23, 2015 3:02 am

Chris Peterson wrote:
HomeAl0ne wrote: ... I seem to remember something about gamma-ray detectors using concentric metal tubes as lenses...
That's how x-ray imaging systems sometimes work (that is, for photons some thousand times less energetic than the sort this gamma ray sensor is designed for). The gamma ray detector detects photons as they plow through thin conductive foil layers...
Click to play embedded YouTube video.
http://imagine.gsfc.nasa.gov/science/toolbox/gamma_detectors2.html wrote: This animation shows how the Large Area Telescope on the Fermi Gamma-ray Telescope works. A gamma ray (purple) interacts with the detector, creating an electron-positron pair which cascade down the tower. Using the paths that the electron and positron take through the telescope, the direction of the original gamma-ray can be determined (shown in purple). (Credit: NASA's Goddard Space Flight Center Conceptual Image Lab)
A pessimist is nothing more than an experienced optimist

User avatar
DavidLeodis
Perceptatron
Posts: 1169
Joined: Mon May 01, 2006 1:00 pm

Re: APOD: Gamma-ray Rain from 3C 279 (2015 Jul 22)

Post by DavidLeodis » Thu Jul 23, 2015 7:37 pm

It's an interesting video. I now though find I'm mentally singing "Gamma-ray rain drops keep falling on my head...." :). It's also making me think of the photon torpedoes used in Star Trek :wink:.