The "Magnetism" of Neutron Stars
Yashwant Gupta, National Centre for Radio Astrophysics (TIFR), Pune

Magnetic fields are an important ingredient of most astrophysical systems and phenomena. In the exotic objects called neutron stars, we find evidence for the strongest magnetic fields encountered in astrophysics. This talk will cover basic ideas about neutron stars, and describe how we infer various properties of these super dense, rapidly rotating objects, including how we estimate the strength and structure of their magnetic fields. We will see how these super-strong magnetic fields play a central role in the physics of neutron stars, being primarily responsible for the generation of the beams of radio radiation which enable us to detect these stars as "radio pulsars".

These radio beams, believed to originate from regions near the north and south poles of the dipolar magnetic field of the pulsar, are seen as a pulse of radiation once every rotation of the star, much like the perodic flashes from a lighthouse. To decode the unsolved mystery of the emission process that produces these intense radio waves, we need to determine more precisely the location of the radiating spots in the polar region of the star, as well as their height above the surface of the star. Results from our detailed study of some pulsars lead to the conclusion that these regions are arranged as concentric cones around the magnetic axis, and are emitted at altitudes of a few hundred kilometers above the surface of the 10 km size star. These results compare well with some of the theoretical models which throw some light on the physics of the pulsar emission mechanism.

Lastly, the talk will touch upon an even more extreme form of neutron stars called "magnetars".

References :
Gupta, Y., Gil, J., Kijak, J. & Sendyk, M. : ``Unraveling the drift behaviour of the remarkable pulsar PSR B0826-34'', published in Astronomy & Astrophysics, vol. 426, p. 229 (2004).

Gupta, Y. & Gangadhara, R. T. : ``Understanding the Radio Emission Geometry of Multiple-Component Radio Pulsars from Retardation and Aberration Effects'', published in the Astrophysical Journal, vol. 584, p. 418 (2003).

Gangadhara, R.T. & Gupta, Y. : ``Understanding the Radio Emission Geometry of PSR B0329+54'', published in the Astrophysical Journal, vol. 555, p. 31 (2001).

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