Nature of anomalous X-ray pulsars, soft gamma repeaters and radio pulsars with very long periods

Details Nature of anomalous X-ray pulsars, soft gamma repeaters and radio pulsars with very long periods Nature of anomalous X-ray pulsars, soft gamma repeaters and radio pulsars with very long periods

Feb 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26at...25....7m&link_type=abstract

Astronomical and Astrophysical Transactions, vol. 25, Issue 1, p.7-31

Astronomy and Astrophysics

Astronomy

5

Anomalous X-Ray Pulsars, Soft Gamma Repeaters, Radio Pulsars, Magnetic Fields, Drift Waves

Scientific paper

A brief review of the known models for the description of anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) is given. A new model is proposed to explain the main properties of these objects on the basis of the concept of drift waves in the vicinity of the light cylinder of the neutron star with a surface magnetic field of about 1012G. In the framework of this model, the rotation periods P, their derivatives d P/d t and the magnetic fields B in the regions of generation of emission observed in AXPs and SGRs are calculated. The intervals for these parameters are P = 11 - 737ms, d P/d t = 3.7 × 10- 16 - 5.5 × 10- 12 and log B = 2.63 - 6.25. A modulation with periods P could be observed in the sources under consideration. The magnetic fields at the neutron star's surface calculated in the framework of the dipole model for AXPs and SGRs have the same order ( = 11.90) as for normal radio pulsars. Pulsars of the types under consideration must have short periods (P ≈ 0.1s) and a small angle β between the rotation and magnetic axes (β < 10°). It is expected that the fraction of these pulsars in the all-pulsar population must be of the order of 0.01. This estimate is in a good agreement with the known number of AXPs and SGRs. It is shown that the cyclotron radiation of electrons near the surface of a neutron star with a magnetic field of about 1012G enables us to explain the observed quiescent X-ray emission of AXPs and SGRs. The pulsed emission is generated by the synchrotron mechanism near the light cylinder. Cataclysms on the neutron star can cause short gamma-ray bursts with a power exceeding the X-ray power by 2γ2 times. Here, γ is the Lorentz factor of the emitting electrons. It is shown that in the magnetar model the electron cyclotron line with an energy of about 1MeV must be formed. Its detection provides good evidence for this model. The drift waves near the light cylinder can cause modulation of the emission with periods of the order of several seconds in radio pulsars as well. These periods explain the intervals between successive pulses observed in radio pulsars with long periods P between the observed pulses (P > 4s). The model under consideration allows us to calculate the real rotation periods of host neutron stars. They are of the order of 1s for the investigated objects. The magnetic fields at the surface of the neutron star are of the order of 1011 1013G and equal to the fields usual for normal radio pulsars.

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