Crab nebula

T. Gold identifies spin-down of central pulsar as energy source for Crab Nebula. 

In 1919 Landmark estimated the distance to the Andromeda galaxy at some 700000 light-years. (Current estimates put it at 2 million light-years.) It was clear that Hartwig s star was a thousand times brighter than any known nova. It was the same Landmark who suggested a connection between the supernova observed by Chinese astronomers in 1054 (the year of the religious schism) and the Crab nebula. 

An interstellar dust cloud containing aligned particles may be looked upon as a linearly birefringent (and possibly linearly dichroic) medium (van de Hulst, 1957, p. 58) the cloud acts like a retarder. We showed at the end of Section 2.11 that linearly polarized light becomes circularly polarized upon transmission by a retarder. The first clear evidence for this kind of polarization mechanism was reported by Martin (1972), where light from the Crab Nebula was the source of linearly polarized incident light. 

The shock wave of fresh debris from a supernova explosion travels a great distance. For example, it has been calculated that the Crab Nebula will attain a diameter of 70 light years 23,000 years from now 140 light years in 260,000 years 210 light years in 1.3 million years and 280 light years in 4 million years. After that the expanding shell will begin to dissipate because the velocity of expansion drops to about 1-2 miles/sec. (3,600-7,200 miles/hr.), which is the velocity of the molecules of interstellar gas. 

The Crab Nebula is the most noticeable object in our Galaxy, and the remnant of the famous Chinese guest star appeared in 1054AD, the best association between supernova remnants(SNR) and ancient guest stars. Before seventies, the Crab Nebula was considered as a special SNR with different morphology and physical features from that of most SNRs, Now more and more Crab-like SNRs have been detected(Weiler 1985). It is necessary to make a systematical investigation for the Crab-like SNRs, especially for those with central pulsars because they offer us more physical messages than others. 

Weiler, K.W., 1985, in The Crab Nebula and Related Supernova Remnants, Kafatos, M.and Henry, R. Ed. (Cambridge Univ. Press, London)... 

This image of the Crab Nebula taken by the Hubble Space Telescope shows enormous interstellar gas clouds, in which spallation reactions may be taking place. 

This is precisely what we see in the Crab Nebula. The rate of the flashes indicates the neutron star is spinning 30 times per second. (Compare that with the Sun s rotation period of about one month.) If a pulsar s beam never sweeps past our line of sight, however, we will never see it. 

The Milagro detector s large field of view and continuous duty cycle make it an ideal instrument for the discovery of previously unknown sources. Recent publications cover topics including detection of the Crab Nebula[l], limits on TeV emission from GRB [2] and a TeV all-sky survey of the northern celestial hemisphere[3]. Recently we have presented papers on the detection of diffuse TeV emission from the Galactic plane[4], limits on TeV emission from satellite detected GRB[5], a study of nearby AGN[6] and limits on relic neutralino annihilation derived from TeV flux limits from the sun[7]. The focus of this paper is the search for extended sources of TeV gamma rays with the Milagro detector. 

The Milagro collaboration has developed a standard set of cuts that this analysis utilizes. The cuts were optimized using studies of the detector simulation and confirmed through observation of the Crab Nebula [1] and Markarian 421 [6], Events with greater than or equal to 20 PMT hits utilized by the shower... 

Figure 5. Significance map of the region containing the Crab nebula (RA=84.6°, 6=22.0°) and...

The MAGIC telescope is in commissioning phase until October 2004. For that reason, two established TeV sources such as the Crab Nebula and the blazar Mrk421, have been observed extensively, in order to assess the telescope performance such as the angular resolution, the sensitivity and the energy threshold. This report, which presents an analysis based in a restricted sub-sample of Crab Nebula and Mrk421 data, is concerned with the first observations and detections by the MAGIC telescope. 

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. 

Figure 6. ALPHA distribution of Crab Nebula events after selection cuts. ON...

Conclusions and Outlook. The established TeV sources Crab Nebula and Mrk421 have been clearly detected by the MAGIC telescope during its com-... 

Crab nebula. The Crab Nebula, first detected in the TeV regime by the Whipple experiment in 1989 (Weekes, 1989), is the standard candle of the... 

Figure 1. Left Detection plot of the Crab Nebula from the H.E.S.S. 2003 data set. Shown is the number of detected events vs. the squared angular distance to the source position for the signal region and a control background region (grey shaded). Right Differential energy spectrum. The dashed line is a power law fit to the data, which yields a spectral index of T = 2.63 0.04 and an integral flux above 1 TeV of = (1.98 0.07) 10 7m 2s-1.

Aharonian, F. A., Akhperjanian, A. G., Barrio, J. A., et al. (2000). The Energy Spectrum of TeV Gamma Rays from the Crab Nebula as measured by the HEGRA System of imaging air Cerenkov Telescopes. The Astrophysical Journal, 539 317. 

Tavernet, J. P. and The CAT Collaboration (1998). Measurement of the Gamma-ray Spectrum of the Crab Nebula Above 250 GEV with the CAT Cherenkov Telescope. In Abstracts of the 19th Texas Symposium on Relativistic Astrophysics and Cosmology, held in Paris, France, Dec. 14-18, 1998. Eds. J. Paul, T. Montmerle, andE. Aubourg (CEA Saclay). 

Weekes, T. C. (1989). Observation of TeV gamma rays from the Crab Nebula using the atmospheric Cherenkov imaging technique. The Astrophysical Journal, 342 379. 

FIGURE 1 Aristotle s Four Elements and Their Qualities. Aristotle hypothesized that the four basic elements arose from the initial chaos under the influence of four fundamental qualities of matter hot, cold, wet, and dry. The central image representing the initial chaos is taken from a United States National Aeronautics and Space Administration (NASA) photograph of the heart of the Crab Nebula, as viewed by the Hubble Telescope in 1995. The Crab Nebula was first viewed from earth in the year 1054, as recorded by Chinese astronomers. Rock paintings by Native Americans show that they also observed its appearance. Actually, the Crab Nebula was a giant star that exploded as a supernova. The variations in color are caused by chemical elements, created during the life and the explosion of the star. Modern-day astronomers believe that the chemical elements in the earth and in our bodies were made by the explosion of stars billions of years ago. Earth. A Air. A Fire. Water. (D.N.Sherwood)... 

Circular polarization in the diffuse ISM first was discovered along the line of sight to the Crab Nebula [23] and several stars [24], and Martin described the mechanism for its production [15]. The circular polarization is hnked to the hnear polarization by the Kramers-Kr n ig relationships and thus in itself does not provide any independent information about the dust grain properties. Martin found that there was a reversal in the sign of circular polarization, at... 

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