Crab Nebula

Fig. 1: X-ray image taken with Chandra of Crab Nebula

The standard Crab Nebula model for high energy emission predicts soft gamma-rays to come predominantly from the magetized plasma torus (shown by the green ring) around the Crab Pulsar (white dot at the center). Pulsar wind is expected to flow predominantly along the rotation axis (represented by 4 straight arrows). High energy electrons trapped in the plasma torus are likely to move along the circular arrows. The diameter of the torus is about 20-30 arc second.

The time-average polarization of X-rays from Crab Nebula has been measured by Weisskopf et al. (1976) at 2.6keV and 5.2keV. The polarization position angles (angle relative to the North) are 161.1+/-2.8 deg (2.6keV) and 155.5 +/- 6.6 deg (5.2keV) and shown by light blue arrows. The model shown in Fig.1 expects the position angle to line up along the rotation axis of the Crab Pulsar (shown by the pink arrow) as photon energy enters the soft gamma-ray band.

Fig. 3: Modulation curve expected with the engineering flight with the 61-PDC and

217-PDC PoGOLite

The polarization position angle will be measure to ~4.7 deg and ~2.4 deg with the 61-PDC and 217-PDC PoGOLite and the long-standing paradigm of the Crab Nebula high-energy emission coming from electrons trapped in the torus (torii) will be tested. 

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Last modified by T. Kamae on March 9, 2008

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