6 research outputs found
Are the magnetic fields of millisecond pulsars ~ 10^8 G?
It is generally assumed that the magnetic fields of millisecond pulsars
(MSPs) are G. We argue that this may not be true and the fields
may be appreciably greater. We present six evidences for this: (1) The G field estimate is based on magnetic dipole emission losses which is
shown to be questionable; (2) The MSPs in low mass X-ray binaries (LMXBs) are
claimed to have G on the basis of a Rayleygh-Taylor instability
accretion argument. We show that the accretion argument is questionable and the
upper limit G may be much higher; (3) Low magnetic field neutron
stars have difficulty being produced in LMXBs; (4) MSPs may still be accreting
indicating a much higher magnetic field; (5) The data that predict G for MSPs also predict ages on the order of, and greater than, ten
billion years, which is much greater than normal pulsars. If the predicted ages
are wrong, most likely the predicted G fields of MSPs are wrong;
(6) When magnetic fields are measured directly with cyclotron lines in X-ray
binaries, fields G are indicated. Other scenarios should be
investigated. One such scenario is the following. Over 85% of MSPs are
confirmed members of a binary. It is possible that all MSPs are in large
separation binaries having magnetic fields G with their magnetic
dipole emission being balanced by low level accretion from their companions.Comment: 16 pages, accept for publication in Astrophysics and Space Scienc
X-ray and optical studies of SAX J1808.4-3658 in quiescence
We have observed the accreting millisecond X-ray pulsar SAX J1808.4-3658 (1808) in quiescence during two 50 ksec XMM-Newton observations, and acquired near-simultaneous photometry with Gemini South. We find 1808's X-ray spectrum to be hard, describable with an absorbed power-law of photon index 1.7-1.9 and unabsorbed X-ray luminosity Lx = 5.2-7.9×10(31) ergs s-1. No thermal neutron star (NS) component is seen, with a limit on any possible NS component of LNS(0.01-10 keV)2.2 Msolar, or for a distance uncertainty 10% larger, of MNS>1.8 Msolar. Such a heavy NS is consistent with the accelerated neutrino cooling found from the X-ray observations