On the timing properties of SAX J1808.4−3658 during its 2015 outburst

Angelo Francesco Gambino, Tiziana Di Salvo, Rosario Iaria, Riggio, Pintore, Sanna, Tailo, Scarano, Burderi, Papitto

Risultato della ricerca: Article

15 Citazioni (Scopus)

Abstract

We present a timing analysis of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1808.4-3658, using non-simultaneous XMM-Newton and NuSTAR observations. We estimate the pulsar spin frequency and update the system orbital solution. Combining the average spin frequency from the previous observed, we confirm the long-term spin-down at an average rate (nu) over dot(SD) = 1.5(2) x 10(-15) Hz s(-1). We also discuss possible corrections to the spin-down rate accounting for mass accretion on to the compact object when the system is X-ray active. Finally, combining the updated ephemerides with those of the previous outbursts, we find a long-term orbital evolution compatible with a binary expansion at a mean rate. P-orb = 3.6(4) x 10(-12) s s(-1), in agreement with previously reported values. This fast evolution is incompatible with an evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. We discuss the observed orbital expansion in terms of non-conservative mass transfer and gravitational quadrupole coupling mechanism. We find that the latter can explain, under certain conditions, small fluctuations (of the order of few seconds) of the orbital period around a global parabolic trend. At the same time, a non-conservative mass transfer is required to explain the observed fast orbital evolution, which likely reflects ejection of a large fraction of mass from the inner Lagrangian point caused by the irradiation of the donor by the magnetodipole rotator during quiescence (radio-ejection model). This strong outflow may power tidal dissipation in the companion star and be responsible of the gravitational quadrupole change oscillations.
Lingua originaleEnglish
pagine (da-a)463-477
Numero di pagine15
RivistaMonthly Notices of the Royal Astronomical Society
Volume471
Stato di pubblicazionePublished - 2017

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outburst
time measurement
mass transfer
orbitals
ejection
pulsars
tidal power
quadrupoles
ephemerides
companion stars
angular momentum
expansion
dissipation
XMM-Newton telescope
irradiation
outflow
gravitational waves
oscillation
accretion
newton

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cita questo

On the timing properties of SAX J1808.4−3658 during its 2015 outburst. / Gambino, Angelo Francesco; Di Salvo, Tiziana; Iaria, Rosario; Riggio; Pintore; Sanna; Tailo; Scarano; Burderi; Papitto.

In: Monthly Notices of the Royal Astronomical Society, Vol. 471, 2017, pag. 463-477.

Risultato della ricerca: Article

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abstract = "We present a timing analysis of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1808.4-3658, using non-simultaneous XMM-Newton and NuSTAR observations. We estimate the pulsar spin frequency and update the system orbital solution. Combining the average spin frequency from the previous observed, we confirm the long-term spin-down at an average rate (nu) over dot(SD) = 1.5(2) x 10(-15) Hz s(-1). We also discuss possible corrections to the spin-down rate accounting for mass accretion on to the compact object when the system is X-ray active. Finally, combining the updated ephemerides with those of the previous outbursts, we find a long-term orbital evolution compatible with a binary expansion at a mean rate. P-orb = 3.6(4) x 10(-12) s s(-1), in agreement with previously reported values. This fast evolution is incompatible with an evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. We discuss the observed orbital expansion in terms of non-conservative mass transfer and gravitational quadrupole coupling mechanism. We find that the latter can explain, under certain conditions, small fluctuations (of the order of few seconds) of the orbital period around a global parabolic trend. At the same time, a non-conservative mass transfer is required to explain the observed fast orbital evolution, which likely reflects ejection of a large fraction of mass from the inner Lagrangian point caused by the irradiation of the donor by the magnetodipole rotator during quiescence (radio-ejection model). This strong outflow may power tidal dissipation in the companion star and be responsible of the gravitational quadrupole change oscillations.",
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T1 - On the timing properties of SAX J1808.4−3658 during its 2015 outburst

AU - Gambino, Angelo Francesco

AU - Di Salvo, Tiziana

AU - Iaria, Rosario

AU - Riggio, null

AU - Pintore, null

AU - Sanna, null

AU - Tailo, null

AU - Scarano, null

AU - Burderi, null

AU - Papitto, null

PY - 2017

Y1 - 2017

N2 - We present a timing analysis of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1808.4-3658, using non-simultaneous XMM-Newton and NuSTAR observations. We estimate the pulsar spin frequency and update the system orbital solution. Combining the average spin frequency from the previous observed, we confirm the long-term spin-down at an average rate (nu) over dot(SD) = 1.5(2) x 10(-15) Hz s(-1). We also discuss possible corrections to the spin-down rate accounting for mass accretion on to the compact object when the system is X-ray active. Finally, combining the updated ephemerides with those of the previous outbursts, we find a long-term orbital evolution compatible with a binary expansion at a mean rate. P-orb = 3.6(4) x 10(-12) s s(-1), in agreement with previously reported values. This fast evolution is incompatible with an evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. We discuss the observed orbital expansion in terms of non-conservative mass transfer and gravitational quadrupole coupling mechanism. We find that the latter can explain, under certain conditions, small fluctuations (of the order of few seconds) of the orbital period around a global parabolic trend. At the same time, a non-conservative mass transfer is required to explain the observed fast orbital evolution, which likely reflects ejection of a large fraction of mass from the inner Lagrangian point caused by the irradiation of the donor by the magnetodipole rotator during quiescence (radio-ejection model). This strong outflow may power tidal dissipation in the companion star and be responsible of the gravitational quadrupole change oscillations.

AB - We present a timing analysis of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1808.4-3658, using non-simultaneous XMM-Newton and NuSTAR observations. We estimate the pulsar spin frequency and update the system orbital solution. Combining the average spin frequency from the previous observed, we confirm the long-term spin-down at an average rate (nu) over dot(SD) = 1.5(2) x 10(-15) Hz s(-1). We also discuss possible corrections to the spin-down rate accounting for mass accretion on to the compact object when the system is X-ray active. Finally, combining the updated ephemerides with those of the previous outbursts, we find a long-term orbital evolution compatible with a binary expansion at a mean rate. P-orb = 3.6(4) x 10(-12) s s(-1), in agreement with previously reported values. This fast evolution is incompatible with an evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. We discuss the observed orbital expansion in terms of non-conservative mass transfer and gravitational quadrupole coupling mechanism. We find that the latter can explain, under certain conditions, small fluctuations (of the order of few seconds) of the orbital period around a global parabolic trend. At the same time, a non-conservative mass transfer is required to explain the observed fast orbital evolution, which likely reflects ejection of a large fraction of mass from the inner Lagrangian point caused by the irradiation of the donor by the magnetodipole rotator during quiescence (radio-ejection model). This strong outflow may power tidal dissipation in the companion star and be responsible of the gravitational quadrupole change oscillations.

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