Orbital evolution of an accreting millisecond pulsar: witnessing the banquet of a hidden black widow?

Tiziana Di Salvo, Burderi, Menna, Papitto, Riggio

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Abstract

We have performed a timing analysis of all the four X-ray outbursts from the accreting millisecond pulsar SAX J1808.4-3658 observed so far by the Proportional Counter Array on board the Rossi X-ray Timing Explorer. For each of the outbursts, we derived the best-fitting value of the time of ascending node passage. We find that these times follow a parabolic trend, which gives an orbital-period derivative , and a refined estimate of the orbital period, Porb = 7249.156499 +/- 1.8 × 10-5 s (reference epoch T0 = 50914.8099 MJD). This derivative is positive, suggesting a degenerate or fully convective companion star, but is more than one order of magnitude higher than what is expected from secular evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. Using simple considerations on the angular momentum of the system, we propose an explanation of this puzzling result assuming that during X-ray quiescence the source is ejecting matter (and angular momentum) from the inner Lagrangian point. We have also verified that this behaviour is in agreement with a possible secular evolution of the system under the hypothesis of highly non-conservative mass transfer. In this case, we find stringent constraints on the masses of the two components of the binary system and its inclination. The proposed orbital evolution indicates that in this kind of sources the neutron star is capable to efficiently ablate the companion star, suggesting that this kind of objects are part of the population of the so-called black widow pulsars, still visible in X-rays during transient mass-accretion episodes.
Lingua originaleEnglish
pagine (da-a)1851-1857
Numero di pagine7
RivistaMonthly Notices of the Royal Astronomical Society
Volume389
Stato di pubblicazionePublished - 2008

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pulsars
companion stars
angular momentum
orbitals
mass transfer
time measurement
outburst
x rays
X Ray Timing Explorer
proportional counters
gravitational waves
neutron stars
inclination
trends
accretion
estimates

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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@article{be423a3b88974dbbbb994d563d4ad2a7,
title = "Orbital evolution of an accreting millisecond pulsar: witnessing the banquet of a hidden black widow?",
abstract = "We have performed a timing analysis of all the four X-ray outbursts from the accreting millisecond pulsar SAX J1808.4-3658 observed so far by the Proportional Counter Array on board the Rossi X-ray Timing Explorer. For each of the outbursts, we derived the best-fitting value of the time of ascending node passage. We find that these times follow a parabolic trend, which gives an orbital-period derivative , and a refined estimate of the orbital period, Porb = 7249.156499 +/- 1.8 × 10-5 s (reference epoch T0 = 50914.8099 MJD). This derivative is positive, suggesting a degenerate or fully convective companion star, but is more than one order of magnitude higher than what is expected from secular evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. Using simple considerations on the angular momentum of the system, we propose an explanation of this puzzling result assuming that during X-ray quiescence the source is ejecting matter (and angular momentum) from the inner Lagrangian point. We have also verified that this behaviour is in agreement with a possible secular evolution of the system under the hypothesis of highly non-conservative mass transfer. In this case, we find stringent constraints on the masses of the two components of the binary system and its inclination. The proposed orbital evolution indicates that in this kind of sources the neutron star is capable to efficiently ablate the companion star, suggesting that this kind of objects are part of the population of the so-called black widow pulsars, still visible in X-rays during transient mass-accretion episodes.",
keywords = "stars: magnetic fields , stars: neutron , pulsars: general , pulsars: individual: SAX J1808.4-3658 , X-rays: binaries",
author = "{Di Salvo}, Tiziana and Burderi and Menna and Papitto and Riggio",
year = "2008",
language = "English",
volume = "389",
pages = "1851--1857",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",

}

TY - JOUR

T1 - Orbital evolution of an accreting millisecond pulsar: witnessing the banquet of a hidden black widow?

AU - Di Salvo, Tiziana

AU - Burderi, null

AU - Menna, null

AU - Papitto, null

AU - Riggio, null

PY - 2008

Y1 - 2008

N2 - We have performed a timing analysis of all the four X-ray outbursts from the accreting millisecond pulsar SAX J1808.4-3658 observed so far by the Proportional Counter Array on board the Rossi X-ray Timing Explorer. For each of the outbursts, we derived the best-fitting value of the time of ascending node passage. We find that these times follow a parabolic trend, which gives an orbital-period derivative , and a refined estimate of the orbital period, Porb = 7249.156499 +/- 1.8 × 10-5 s (reference epoch T0 = 50914.8099 MJD). This derivative is positive, suggesting a degenerate or fully convective companion star, but is more than one order of magnitude higher than what is expected from secular evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. Using simple considerations on the angular momentum of the system, we propose an explanation of this puzzling result assuming that during X-ray quiescence the source is ejecting matter (and angular momentum) from the inner Lagrangian point. We have also verified that this behaviour is in agreement with a possible secular evolution of the system under the hypothesis of highly non-conservative mass transfer. In this case, we find stringent constraints on the masses of the two components of the binary system and its inclination. The proposed orbital evolution indicates that in this kind of sources the neutron star is capable to efficiently ablate the companion star, suggesting that this kind of objects are part of the population of the so-called black widow pulsars, still visible in X-rays during transient mass-accretion episodes.

AB - We have performed a timing analysis of all the four X-ray outbursts from the accreting millisecond pulsar SAX J1808.4-3658 observed so far by the Proportional Counter Array on board the Rossi X-ray Timing Explorer. For each of the outbursts, we derived the best-fitting value of the time of ascending node passage. We find that these times follow a parabolic trend, which gives an orbital-period derivative , and a refined estimate of the orbital period, Porb = 7249.156499 +/- 1.8 × 10-5 s (reference epoch T0 = 50914.8099 MJD). This derivative is positive, suggesting a degenerate or fully convective companion star, but is more than one order of magnitude higher than what is expected from secular evolution driven by angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. Using simple considerations on the angular momentum of the system, we propose an explanation of this puzzling result assuming that during X-ray quiescence the source is ejecting matter (and angular momentum) from the inner Lagrangian point. We have also verified that this behaviour is in agreement with a possible secular evolution of the system under the hypothesis of highly non-conservative mass transfer. In this case, we find stringent constraints on the masses of the two components of the binary system and its inclination. The proposed orbital evolution indicates that in this kind of sources the neutron star is capable to efficiently ablate the companion star, suggesting that this kind of objects are part of the population of the so-called black widow pulsars, still visible in X-rays during transient mass-accretion episodes.

KW - stars: magnetic fields , stars: neutron , pulsars: general , pulsars: individual: SAX J1808.4-3658 , X-rays: binaries

UR - http://hdl.handle.net/10447/45200

UR - http://adsabs.harvard.edu/abs/2008MNRAS.389.1851D

M3 - Article

VL - 389

SP - 1851

EP - 1857

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

ER -