How Common Are Magnetars? The Consequences of Magnetic Field Decay

Ultramagnetized neutron stars, or magnetars, have been invoked to explain several astrophysical phenomena. We examine how the magnetic field of a magnetar will decay over time and how this decay affects the cooling of the object. We find that for sufficiently strong nascent fields, field decay alters significantly the cooling evolution relative to similarly magnetized neutron stars with constant fields. As a result, old magnetars can be expected to be bright in the soft X-ray band. The soft X-ray source RX J0720.4-3125 may well be the nearest such old magnetar.

[1]  D. Frail,et al.  Identification of a supernova remnant coincident with the soft γ-ray repeater SGR1806 - 20 , 1993, Nature.

[2]  Direct URCA process in neutron stars with strong magnetic fields , 1997, astro-ph/9711216.

[3]  D. Melrose,et al.  Bound Pair Creation in Polar Gaps and Gamma-Ray Emission from Radio Pulsars , 1996 .

[4]  L. Hernquist.  Relativistic electron transport in a quantizing magnetic field , 1984 .

[5]  J. Heyl,et al.  Powering Anomalous X-Ray Pulsars by Neutron Star Cooling , 1997, astro-ph/9708179.

[6]  Andreas Reisenegger,et al.  Magnetic field decay in isolated neutron stars , 1992 .

[7]  C. Thompson,et al.  The soft gamma repeaters as very strongly magnetized neutron stars - I. Radiative mechanism for outbursts , 1995 .

[8]  R. Narayan.  The birthrate and initial spin period of single radio pulsars , 1987 .

[9]  C. Kouveliotou,et al.  The rarity of soft γ-ray repeaters deduced from reactivation of SGR1806 – 20 , 1994, Nature.

[10]  Van Riper,et al.  Magnetic neutron star atmospheres , 1988 .

[11]  S. Kulkarni,et al.  Discovery of an X-ray source coincident with the soft γ-ray repeater 0525 – 66 , 1994, Nature.

[12]  F. Haberl,et al.  Isolated neutron stars in the ROSAT Survey , 1998 .

[13]  Christopher Thompson,et al.  The Soft Gamma Repeaters as Very Strongly Magnetized Neutron Stars. II. Quiescent Neutrino, X-Ray, and Alfvén Wave Emission , 1996 .

[14]  G. Vasisht,et al.  The Discovery of an Anomalous X-Ray Pulsar in the Supernova Remnant Kes 73 , 1997, astro-ph/9706058.