| Issue |
A&A
Volume 397, Number 2, January II 2003
|
|
|---|---|---|
| Page(s) | 723 - 727 | |
| Section | Stellar structure and evolution | |
| DOI | https://doi.org/10.1051/0004-6361:20021491 | |
| Published online | 17 December 2002 | |
Constraints on the neutron star magnetic field of the two X-ray transients SAX J1808.4–3658 and Aql X–1
1
Astronomical Institute “Anton Pannekoek”, University of Amsterdam and Center for High-Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: disalvo@astro.uva.nl
2
Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy e-mail: burderi@coma.mporzio.astro.it
Corresponding author: T. Di Salvo, disalvo@astro.uva.nl
Received:
28
August
2002
Accepted:
11
October
2002
The recently discovered coherent X-ray pulsations at a frequency of
~400 Hz in SAX J1808.4–3658, together with a measure of the source luminosity
in quiescence, allow us to put an upper limit on the neutron star magnetic
field, that is 
Gauss, using simple considerations on
the position of the magnetospheric radius during quiescent periods. Combined
with the lower limit inferred from the presence of X-ray pulsations,
this constrains the SAX J1808.4–3658 neutron star magnetic field in the quite
narrow range 
Gauss. Similar considerations applied to the
case of Aql X–1 give a neutron star magnetic field lower than ~109 Gauss.
Key words: accretion disks / stars: individual: SAX J1808.4–3658, Aql X–1 / stars: neutron / X-rays: stars / X-rays: binaries / X-rays: general
© ESO, 2003
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