Constraints on the neutron star magnetic field of the two X-ray transients SAX J1808.4–3658 and Aql X–1

Salvo, T. Di; Burderi, L.

doi:10.1051/0004-6361:20021491

Cited by 49 publications

(48 citation statements)

References 43 publications

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“…We can therefore evaluate the magnetic moment, µ, of SAX J1808.4-3658 from our measured value of the spin-down, using the relation µ 2 /(9R 3 CO ) = 2πIν sd , where R CO is the corotation radius. The magnetic field found in this way is B ∼ (3.5 ±0.5) ×10 8 Gauss, perfectly in agreement with previous constraints [13].…”

Section: Sax J18084-3658supporting

confidence: 92%

Order in the chaos? The strange case of accreting millisecond pulsars

Salvo¹,

Burderi²,

Riggio³

et al. 2007

AIP Conference Proceedings

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Abstract. We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, we derive information on the mass accretion rate and magnetic field of the neutron star in these systems. We also find that the phase delays behavior as a function of time in these sources is sometimes quite complex and difficult to interpret, since phase shifts, most probably driven by variations of the X-ray flux, are sometimes present.

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Section: Sax J18084-3658supporting

confidence: 92%

Order in the chaos? The strange case of accreting millisecond pulsars

Salvo¹,

Burderi²,

Riggio³

et al. 2007

AIP Conference Proceedings

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“…the radius at which an object corotating with the NS attains the speed of light; see Ruderman et al 1989;Illarionov & Sunyaev 1975). Di Salvo & Burderi (2003) have shown that a magneto-dipole rotator can easily be active in SAX J1808.4-3658 during quiescence. In fact, for a luminosity in quiescence of ∼5 × 10 31 ergs/s (Campana et al 2002), the NS surface magnetic field should be B < ∼ 0.05 × 10 8 Gauss in order to truncate the disk inside the corotation radius and allow accretion Letter to the Editor onto the NS surface.…”

Section: Irradiation Of the Disk And Companion Star By Rotating Magnementioning

confidence: 99%

“…To this aim we need an estimate of the NS magnetic field in this system. As mentioned above, from a measure of the source luminosity in quiescence and using simple considerations on the position of the magnetospheric radius during quiescent periods, it is possible to estimate an upper limit on the NS magnetic field of B < ∼ 5 × 10 8 Gauss (Di Salvo & Burderi 2003). This, together with the lower limit mentioned above, constrains the SAX J1808.4-3658 NS magnetic field in the quite narrow range (1−5) × 10 8 Gauss.…”

Section: Irradiation Of the Disk And Companion Star By Rotating Magnementioning

confidence: 99%

The optical counterpart to SAX J1808.4–3658 in quiescence: Evidence of an active radio pulsar?

Burderi

Salvo

D’Antona

et al. 2003

A&A

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116

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Abstract. The optical counterpart of the binary millisecond X-ray pulsar SAX J1808.4-3658 during quiescence was detected at V = 21.5 mag by Homer et al. (2001). This star shows a 6% semi-amplitude sinusoidal modulation of its flux at the orbital period of the system. It was proposed that the modulation arises from X-ray irradiation of the intrinsically faint companion by a remnant accretion disk, and that the bulk of the optical emission arises from viscous dissipation in the disk. The serious difficulty in this scenario lies in the estimate of the irradiating luminosity required to match the observational data, that is a factor 10−50 higher than the quiescent X-ray luminosity of this source. To overcome this problem, we propose an alternative scenario, in which the irradiation is due to the release of rotational energy by the fast spinning neutron star, switched on, as magneto-dipole rotator (radio pulsar), during quiescence. Our computations indicate that the optical magnitudes are fully consistent with this hypothesis. In this case the observed optical luminosity may be the first evidence that a radio pulsar is active in this system in quiescence, a key phase for understanding the evolution of this class of objects.

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“…This is true, obviously, only if the binary system was a NS-main sequence binary: in systems where the companion is a white dwarf, and that evolve from short periods towards long periods and do not evolve though a pulsar phase. For instance, the surface magnetic field of the first millisecond X-ray pulsar discovered, SAX J1808.4-3658 [14], has been estimated to be in the range (1 − 5) × 10 8 G [15]. If this system has a MS companion, so that it evolved from longer orbital periods, it cannot be supramassive, as it survived the period gap.…”

Section: Evolution Of Low Mass X-ray Binaries Towards Short Orbital Pmentioning

confidence: 99%

General relativistic effects on the evolution of binary systems

Lavagetto

Burderi

D’Antona

et al. 2005

AIP Conference Proceedings

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Abstract. When a radio pulsar brakes down due to magnetodipole emission,its gravitational mass decreases accordingly. If the pulsar is hosted in a binary system, this mass loss will increase the orbital period of the system. We show that this relativistic effect can be indeed observable if the neutron star is fast and magnetized enough and that, if observed, it will help to put tight constraints to the equation of state of ultradense matter. Moreover, in Low Mass X-ray Binaries that evolve towards short periods, the neutron star lights up as a radio pulsar during the "period gap". As the effect we consider contrasts the orbital period decay, the system spends a longer time in this phase. As a consequence, the neutron star can survive this phase only if it is non-supramassive. Since in such bianries ∼ 0.8M can be accreted onto the neutron star, short period (P ≤ 2 h) millisecond Xray pulsars like SAX J1808.4-3658 can be formed only if either a large part of the accreting matter has been ejected from the system, or the equation of state of ultradense matter is very stiff.

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Constraints on the neutron star magnetic field of the two X-ray transients SAX J1808.4–3658 and Aql X–1

Cited by 49 publications

References 43 publications

Order in the chaos? The strange case of accreting millisecond pulsars

Order in the chaos? The strange case of accreting millisecond pulsars

The optical counterpart to SAX J1808.4–3658 in quiescence: Evidence of an active radio pulsar?

General relativistic effects on the evolution of binary systems

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