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Scope


Overview


The Sun


Jupiter


The Moon


Galactic Hydrogen Line


Galactic Continuum Emissions


SuperNova Remnants


Thermal Emission Nebulae


Pulsars


Extra-Galactic Sources


Conclusions


References

Supernova Remnants

Supernova remnants are vast almost spherical shells of plasma moving with extremely high velocity into space as a result of high mass stellar explosion. The plasma moves - and carries with it - a significant magnetic field with which the plasma interacts to produce strong synchrotron emissions. As the relativistic plasma shock wave slams into the surrounding tenuous interstellar material further emissions are generated. There are a number of well known supernova remnants in our galaxy, some of which make good observing 'targets' for the amateur radio astronomer.

Name
Light reached Earth
Distance Ly
Cassiopeia A
17th C
10,000
Crab Nebula SN1054
1054 AD
6,300
Tycho’s SN1572
1572 AD
7,500
Sagittarius A (E)
?
26,000
Veil Nebula
>3600BC
1,400 – 2,600
Kepler’s SN1604
1604
20,000
Vela SNR
11th – 9th Millennium BC
800

 

Some of these sources are too difficult for the amateur to observe: either they are too weak or at too low a declination for observers in the UK. For example, Sagittarius A cannot be observed from the southern UK as it lies too close to the horizon, and ground noise will enter the antenna beam and mask the source. The easiest supernova remnants to detect are Cassiopeia A (Right Ascension: 23:23:21 & Declination: 58:49:59) and Taurus A - the Crab Nebula ( Right Ascension: 05:34:30 & Declination: 22:00:57). Unfortunately they both lie close to the galactic plane and this can make it difficult to separate them out from the integrated galactic emissions. See Figures 8.1 and 8.2(11)

Figure 8.1 Location of Cassiopeia A

Cassiopeia A (3C461) lies in the outer edge of the galactic plane as seen from Earth. It is a very strong source at many wavelengths. In this picture from Radio Eyes(11) its intensity at 408MHz is given as 5500Jy.

Figure 8.2 Location of Taurus A (Crab Nebula)

Taurus A (3C144) also lies in the outer galactic plane and has an intensity at 408MHz of around 1200Jy.

A good way to separate out point-like supernova remnant sources from the galactic background is to use a radio interferometer which will produce 'fringes' from the point source, but not from the widespread background. An example may be seen in Figure 8.3.

Figure 8.3 Separation of Taurus A from galactic background

Note that the 'hump' on which the fringes sit is due to the background emissions from the galactic plane. The fringes can easily be separated out with software as shown in Figure 8.4.

Figure 8.4 Amateur detection of the Crab Nebula

The Crab nebula supernova remnant is a beautiful visual and radio object - See Figures 8.5 & 8.6.

The remains of the original star has collapsed to a Neutron star and is a Pulsar spinning at 30 times at second and emitting its own special radiation pattern, but at levels much below that of the whole supernova remnant. Pulsars will be discussed in section 10.

Figure 8.5 Crab Nebula (optical) Figure 8.6 Crab Nebula Radio @ 5GHz