Evidence for Magnetic Field Decay in RX J0720.4-3125
Abstract
The unidentified X-ray source RX J0720.4-3125 is a candidate isolated neutron star showing evidence for pulsed emission with an 8.39 s period and a spectrum consistent with a blackbody at kT = 80 eV. We show that this source is most likely an old isolated neutron star accreting from surrounding media. We then argue that unless it was born with a long spin period (Pi >~ 0.5 s) and a weak field (Bi <~ 1010 G), the magnetic field on this star must have decayed. With Bi ~ 1012 G, we find decay timescales of >~107 yr for power-law decay and >~108 yr for exponential decay. A measured period derivative Ṗ <~ 10-16 s s-1 would be consistent with an old accreting isolated neutron star. Both power-law and exponential decay models can give a Ṗ ~ 10-16 s s-1, though a Ṗ substantially less than this would be indicative of exponential field decay.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1997
- DOI:
- 10.1086/310852
- arXiv:
- arXiv:astro-ph/9706288
- Bibcode:
- 1997ApJ...486L.119W
- Keywords:
-
- STARS: PULSARS: GENERAL;
- STARS: INDIVIDUAL ALPHANUMERIC: RX J0720.4-3125;
- STARS: MAGNETIC FIELDS;
- STARS: NEUTRON;
- X-RAYS: STARS;
- Subject headings: pulsars: general--stars: individual (RX J0720.4-3125)-- stars: magnetic fields--stars: neutron--X-rays: stars;
- Astrophysics
- E-Print:
- 19 pages, 1 figure, Latex