Crab Pulsar

It will be a straightforward matter to obtain specific results for, say, the Crab pulsar s field, estimated at 6 x 10 G (see, for instance, [1]) should precise data for given fields be needed subsequently, using TF theory in the limit of large B, from which the Table was constructed. 

Crab Nebula. The Crab Nebula was hrst estabbshed as a TeV gamma-ray source by the Whipple telescope in 1989 [21] and for the moment being, is the best hrmly established TeV steady emitter in the northern sky. MAGIC will not use the Crab Nebula only as a standard candle but can also expect interesting physics from it as the detection of the Crab pulsar and the IC peak [22 23] once the 30 GeV energy threshold has been reached. 

Since the Crab pulsar shows pulsed emission in the optical wavelengths with the same frequency as in radio and most probably of VHE 7-rays, here we use the central pixel of HEGRA CT1 to monitor the optical Crab pulsation. 

Figure 1. Observations of the optical Crab pulsar with CT1. On the left, (a) the two peaks are clearly visible in the light curve with a separation in phase of 0.4. On the right (b) the excess in the reduced x2 searching in a wide range of frequencies, using the 15th October ephemeris. The difference between the frequency found with 15th October ephemeris and 15th November is consistent with the drift in the digitization card clock. The inset shows the value of the reduced x2 vs. x = (o — v0)/IFS, where i/0 corresponds to 15th October.

Fig. 2. The minimum detectable degree of polarization in Crab vs. incident photon energy for the INTEGRAL Imager detector observing an un-pulsed source with the time averaged spectrum of the Crab pulsar. The solid line shows the sensitivity for no threshold, while the dashed line shows the sensitivity for a 120 keV threshold.

The Crab pulsar is the most likely source to emit polarized 7-rays which might be detectable to COMPTEL. Its 7-ray emission is best described as (phase averaged) 8.6 ph.s cm kev, which gives a source flux of... 

A simulated observation of the Crab pulsar was performed in the energy band between 0.75 and 5 MeV, assuming the 7-rays are 100% linearly polarized with the electric vector 1] at 0 to the x-axis of COMPTEL. Also it was being observed 15° off axis with the azimuth angle as 0° to the x-axis. The data sets obtained contain 10 unpolarized and 10 polarized events. 

COMPTEL as a 7-ray polarimeter has been investigated by M-C simulations and its polarization response been obtained. It is most sensitive to low energy 7-rays, < 5 MeV. While it may only have a modest Q value, < 0.10, the Crab pulsar can be detected in a two week observation if it is 100% polarized. The fact that there are more than two months data available on the Crab source means there is a very good chance now to tell, at least, whether the 7-rays are polarized or not. 

As long as the core left behind the supernova explosion is less than about three solar masses, the collapse will be stopped by the pressure of degenerate neutrons. Thus a neutron star is formed which is a very compact object with a radius of only 10 km. Pulsars are rapidly rotating neutron stars. A famous example of a supernova remnant is the Crab nebula. The shell of this nebula expands at velocities of up to 1500 km/s. The filaments contain anomalously high abundances of helium and other more massive chemical elements. The Crab Pulsar rotates 30 times a second (see Fig. 8.9). The Crab Pulsar (PSR B0531-I-21) is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054 and it was observed e.g. by ancient Chinese astronomers. 

---