Synchrotron radiation

[Dr. Morbius]

What is it about this type of emission that makes it so interesting to astronomers? Could it be seen by an amateur with a 4.5" reflector and a polarized lens of some kind?

[Chris Peterson]

What is it about this type of emission that makes it so interesting to astronomers?

Since it is produced by relativistic particles (usually electrons) moving in magnetic fields, and is easily detected, it is a very useful probe for the properties of regions where it is emitted. Astronomers are always interested in mechanisms that yield more information than just the intensity alone of light reveals.

Could it be seen by an amateur with a 4.5" reflector and a polarized lens of some kind?

If by "see" you mean through an eyepiece, I'm not aware of any visible light synchrotron sources that are bright enough. With a camera you can certainly detect it. You only need a polarized filter to confirm its presence, not to actually record it.

[neufer]

Could it be seen by an amateur with a 4.5" reflector and a polarized lens of some kind?

If by "see" you mean through an eyepiece, I'm not aware of any visible light synchrotron sources that are bright enough. With a camera you can certainly detect it. You only need a polarized filter to confirm its presence, not to actually record it.

Crab Nebula apparent magnitude (V) +8.4

Explanation: The Crab Nebula resulted from a star that exploded - a supernova. Although the stellar explosion that caused the Crab Nebula was seen over 900 years ago, the nebula itself still expands and shines. Much of the emitted light has been found to be polarized. Light waves with the same polarization vibrate in the same plane. Areas of different polarization above are highlighted by different colors. Mapping the polarization helps astronomers decipher which physical processes create the observed light.

http://antwrp.gsfc.nasa.gov/apod/ap080217.html
http://antwrp.gsfc.nasa.gov/apod/ap061026.html

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The nebula was first observed by John Bevis in 1731, and corresponds to a bright supernova recorded by Chinese and Arab astronomers in 1054. At X-ray and gamma-ray energies above 30 KeV, the Crab is generally the strongest persistent source in the sky, with measured flux extending to above 10^12 eV. Located at a distance of about 6,500 light-years (2 kpc) from Earth, the nebula has a diameter of 11 ly (3.4 pc) and expands at a rate of about 1,500 kilometers per second.

At the center of the nebula lies the Crab Pulsar, a rotating neutron star, which emits pulses of radiation from gamma rays to radio waves with a spin rate of 30.2 times per second. The nebula was the first astronomical object identified with a historical supernova explosion.

Very rarely, Saturn transits the Crab Nebula. Its transit in 2003 was the first since 1296; another will not occur until 2267. Observers used the Chandra X-ray Observatory to observe Saturn's moon Titan as it crossed the nebula, and found that Titan's X-ray 'shadow' was larger than its solid surface, due to absorption of X-rays in its atmosphere. These observations showed that the thickness of Titan's atmosphere is 880 km. The transit of Saturn itself could not be observed, because Chandra was passing through the Van Allen belts at the time.

In visible light, the Crab Nebula consists of a broadly oval-shaped mass of filaments, about 6 arcminutes long and 4 arcminutes wide (by comparison, the full moon is 30 arcminutes across) surrounding a diffuse blue central region. In three dimensions, the nebula is thought to be shaped like a prolate spheroid. The filaments are the remnants of the progenitor star's atmosphere, and consist largely of ionised helium and hydrogen, along with carbon, oxygen, nitrogen, iron, neon and sulfur. The filaments' temperatures are typically between 11,000 and 18,000 K, and their densities are about 1,300 particles per cm³.

In 1953 Iosif Shklovsky proposed that the diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving of electrons moving at speeds up to half the speed of light. Three years later the theory was confirmed by observations. In the 1960s it was found that the source of the electron curved paths was the strong magnetic field produced by a neutron star at the center of the nebula.>>

[Chris Peterson]

Crab Nebula apparent magnitude (V) +8.4

If you're suggesting that the Crab Nebula represents a visible source of synchrotron radiation, I think that's questionable. Only a fraction of the light is from synchrotron radiation, and that in a part of the spectrum that the eye isn't very sensitive to. I've made images of the Crab through polarized filters, and the polarization is apparent. I've also looked at it through the eyepiece using the same filter, and its appearance doesn't change with the angle of polarization. This just isn't a visible effect with M1.

Of course, there are photons coming from various sources that are the product of synchrotron emissions, so technically you can see some of it when looking through a telescope. But I took the question to be a little more practical: is there a way to visually identify synchrotron radiation using a small telescope and polarized filter. My answer to that remains the same: I'm not aware of any sources which are bright enough.

[Dr. Morbius]

Thanks! You guys are the whip!

You are right, my question was a practical one. If I understand your answer, all I need is a polarized lens and a camera to "see' this radiation. I'm assuming that this would be done with a timed exposure since you indicate the sources of this type of emission are not very bright.

Are supernova's the only source of synchrotron radiation? I read somewhere that this type of radiation was first observed on earth in the laboratory. That's pretty amazing. When it is discussed in material on the subject, the term 'relativistic' is used to describe the speed of the particles (electrons?) that emit the polarized radiation. Does this mean they are approaching the speed of light? How could that have been reproduced in a laboratory on earth?

I think that this kind of forum is absolutely outstanding. With all the misunderstanding (and misuse) of science out there, it is comforting to have you guys (and APOD, by the way) as a source of real, honest-to-goodness, information.

Thanks for your time.

[neufer]

Are supernova's the only source of synchrotron radiation? I read somewhere that this type of radiation was first observed on earth in the laboratory. That's pretty amazing. When it is discussed in material on the subject, the term 'relativistic' is used to describe the speed of the particles (electrons?) that emit the polarized radiation. Does this mean they are approaching the speed of light? How could that have been reproduced in a laboratory on earth?

By having very large laboratories:

<<The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator, intended to collide opposing particle beams, of either protons at an energy of 7 TeV per particle, or lead nuclei at an energy of 574 TeV per nucleus. It lies in a tunnel 27 kilometres in circumference, as much as 175 metres beneath the Franco-Swiss border near Geneva, Switzerland.>>

Synchrotron radiation losses are the main reason that
1) circular ultrarelativistic proton accelerators have to be large & underground and
2) ultrarelativistic electron accelerators have to be linear.

<<Synchrotron radiation is electromagnetic radiation, similar to cyclotron radiation, but generated by the acceleration of ultrarelativistic (i.e., moving near the speed of light) charged particles through magnetic fields. This may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields in space. The radiation produced may range over the entire electromagnetic spectrum, from radio waves to infrared light, visible light, ultraviolet light, X-rays, and gamma rays. It is distinguished by its characteristic polarization and spectrum. The radiation was named after its discovery in a General Electric synchrotron accelerator built in 1946 and announced in May 1947 by Frank Elder, Anatole Gurewitsch, Robert Langmuir, and Herb Pollock in a letter entitled "Radiation from Electrons in a Synchrotron"[1]. Pollock recounts:

"On April 24, Langmuir and I were running the machine and as usual were trying to push the electron gun and its associated pulse transformer to the limit. Some intermittent sparking had occurred and we asked the technician to observe with a mirror around the protective concrete wall. He immediately signaled to turn off the synchrotron as "he saw an arc in the tube." The vacuum was still excellent, so Langmuir and I came to the end of the wall and observed. At first we thought it might be due to Cherenkov radiation, but it soon became clearer that we were seeing Ivanenko and Pomeranchuk radiation."

Synchrotron radiation may occur in accelerators either as a nuisance, causing undesired energy loss in particle physics contexts, or as a deliberately produced radiation source for numerous laboratory applications. Electrons are accelerated to high speeds in several stages to achieve a final energy that is typically in the GeV range.

Synchrotron radiation was first detected in a jet emitted by M87 in 1956 by Geoffrey R. Burbidge, who saw it as confirmation of a prediction by Iosif S. Shklovskii in 1953, but it had been predicted several years earlier by Hannes Alfvén and Nicolai Herlofson in 1950.

T. K. Breus noted that questions of priority on the history of astrophysical synchrotron radiation is quite complicated, writing:

"In particular, the Russian physicist V.L. Ginsburg broke his relationships with I.S. Shklovsky and did not speak with him for 18 years. In the West, Thomas Gold and Sir Fred Hoyle were in dispute with H. Alfven and N. Herlofson, while K.O. Kiepenheuer and G. Hutchinson were ignored by them."

(I may not speak to Chris for 18 years. )

[Dr. Morbius]

Again - you guys are the whip at this stuff!

Isn't it funny that the 'mad scientists' had to rely on the 'technician' to help interpret their results?! (Sorry, I'm a biomedical engineering technician, myself!)

Also, thanks for the historical anecdotes regarding the 'discoverers' of synchrotron radiation. Just goes to show that even the most brilliant of us are still only human! And I hope you do speak to Chris sooner that that!

Thanks again

Dr. Morbius

[Chris Peterson]

If I understand your answer, all I need is a polarized lens and a camera to "see' this radiation. I'm assuming that this would be done with a timed exposure since you indicate the sources of this type of emission are not very bright.

Yes, the reason you need a camera is so you can integrate enough light- something the eye isn't good at (its maximum exposure time is around 100 ms; the variable polarization of M1 is quite apparent with just a few minutes total exposure). I've seen amateur images of other objects taken at different polarization angles, as well. I don't recall if these were showing synchrotron radiation or some other polarization mechanism.

Are supernova's the only source of synchrotron radiation?

All you need is relativistic charged particles and a magnetic field. There are a variety of natural phenomena that can provide that combination. Many of these are fairly exotic, like supernova remnants and rapidly spinning neutron stars or black holes, but synchrotron radiation is also generated in Jupiter's magnetic field, and in our own Van Allen belt (in both the latter cases, the radiation is radio frequency, not optical).

When it is discussed in material on the subject, the term 'relativistic' is used to describe the speed of the particles (electrons?) that emit the polarized radiation. Does this mean they are approaching the speed of light?

Yes.

How could that have been reproduced in a laboratory on earth?

That's what particle accelerators do... they produce very high speed (typically relativistic) charged particle streams.

[harry]

G'day from the land of ozzzzzz

Just a bit of add info.

http://arxiv.org/abs/0907.1385
On the very high energy (>25GeV) pulsed emission in the Crab pulsar

Authors: Machabeli George, Osmanov Zaza
(Submitted on 8 Jul 2009 (v1), last revised 11 Jul 2009 (this version, v3))

Abstract: We have examined the recently detected very high energy (VHE) pulsed radiation from the Crab pulsar. According to the observational evidence, the observed emission (>25GeV) peaks at the same phase with the optical spectrum. Considering the cyclotron instability, we show that the pitch angle becomes non-vanishing leading to the efficient synchrotron mechanism near the light cylinder surface. The corresponding spectral index of the emission equals -1/2. By studying the inverse Compton scattering and the curvature radiation, it is argued that the aforementioned mechanisms do not contribute to the VHE radiation detected by MAGIC.

[harry]

G'day

What has that got to do with the price of eggs?