### Abstract

Lingua originale | English |
---|---|

Numero di pagine | 12 |

Rivista | THE ASTROPHYSICAL JOURNAL |

Volume | 836 |

Stato di pubblicazione | Published - 2017 |

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### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Cita questo

*THE ASTROPHYSICAL JOURNAL*,

*836*.

**A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with NuStar.** / Di Salvo, Tiziana; Degenaar; Paerels; Bachetti; Parker, Michael L.; Bostrom; Ludlam; Tomsick; Natalucci; Barret, Didier; Miller, Jon M.; Cackett, Edward M.

Risultato della ricerca: Article

*THE ASTROPHYSICAL JOURNAL*, vol. 836.

}

TY - JOUR

T1 - A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with NuStar

AU - Di Salvo, Tiziana

AU - Degenaar, null

AU - Paerels, null

AU - Bachetti, null

AU - Parker, Michael L.

AU - Bostrom, null

AU - Ludlam, null

AU - Tomsick, null

AU - Natalucci, null

AU - Barret, Didier

AU - Miller, Jon M.

AU - Cackett, Edward M.

PY - 2017

Y1 - 2017

N2 - We present NuSTAR observations of neutron star (NS) low-mass X-ray binaries: 4U 1636-53, GX 17+2, and 4U 1705-44. We observed 4U 1636-53 in the hard state, with an Eddington fraction, F_Edd of 0.01; GX 17+2 and 4U 1705-44 were in the soft state with fractions of 0.57 and 0.10, respectively. Each spectrum shows evidence for a relativistically broadened Fe Kalpha line. Through accretion disk reflection modeling, we constrain the radius of the inner disk in 4U 1636-53 to be R_in = 1.03 +/- 0.03 ISCO (innermost stable circular orbit), assuming a dimensionless spin parameter a* = cJ/(GM^2) = 0.0, and R_in = 1.08 +/- 0.06 ISCO for a* = 0.3 (errors quoted at 1 sigma). This value proves to be model independent. For a* = 0.3 and M = 1.4 Msun, for example, 1.08 ± 0.06 ISCO translates to a physical radius of R = 10.8 +/- 0.6 km, and the NS would have to be smaller than this radius (other outcomes are possible for allowed spin parameters and masses). For GX 17+2, R_in = 1.00-1.04 ISCO for a* = 0.0 and R_in = 1.03-1.30 ISCO for a* = 0.3. For a* = 0.3 and M = 1.4 Msun, R_in = 1.03-1.30 ISCO translates to R = 10.3-13.0 km. The inner accretion disk in 4U 1705-44 may be truncated just above the stellar surface, perhaps by a boundary layer or magnetosphere; reflection models give a radius of 1.46–1.64 ISCO for a* = 0.0 and 1.69–1.93 ISCO for a* = 0.3. We discuss the implications our results may have on the equation of state of ultradense, cold matter and our understanding of the innermost accretion flow onto NSs with low surface magnetic fields, and systematic errors related to the reflection models and spacetime metric around less idealized NSs.

AB - We present NuSTAR observations of neutron star (NS) low-mass X-ray binaries: 4U 1636-53, GX 17+2, and 4U 1705-44. We observed 4U 1636-53 in the hard state, with an Eddington fraction, F_Edd of 0.01; GX 17+2 and 4U 1705-44 were in the soft state with fractions of 0.57 and 0.10, respectively. Each spectrum shows evidence for a relativistically broadened Fe Kalpha line. Through accretion disk reflection modeling, we constrain the radius of the inner disk in 4U 1636-53 to be R_in = 1.03 +/- 0.03 ISCO (innermost stable circular orbit), assuming a dimensionless spin parameter a* = cJ/(GM^2) = 0.0, and R_in = 1.08 +/- 0.06 ISCO for a* = 0.3 (errors quoted at 1 sigma). This value proves to be model independent. For a* = 0.3 and M = 1.4 Msun, for example, 1.08 ± 0.06 ISCO translates to a physical radius of R = 10.8 +/- 0.6 km, and the NS would have to be smaller than this radius (other outcomes are possible for allowed spin parameters and masses). For GX 17+2, R_in = 1.00-1.04 ISCO for a* = 0.0 and R_in = 1.03-1.30 ISCO for a* = 0.3. For a* = 0.3 and M = 1.4 Msun, R_in = 1.03-1.30 ISCO translates to R = 10.3-13.0 km. The inner accretion disk in 4U 1705-44 may be truncated just above the stellar surface, perhaps by a boundary layer or magnetosphere; reflection models give a radius of 1.46–1.64 ISCO for a* = 0.0 and 1.69–1.93 ISCO for a* = 0.3. We discuss the implications our results may have on the equation of state of ultradense, cold matter and our understanding of the innermost accretion flow onto NSs with low surface magnetic fields, and systematic errors related to the reflection models and spacetime metric around less idealized NSs.

UR - http://hdl.handle.net/10447/226038

UR - http://adsabs.harvard.edu/abs/2017ApJ...836..140L

M3 - Article

VL - 836

JO - THE ASTROPHYSICAL JOURNAL

JF - THE ASTROPHYSICAL JOURNAL

SN - 1538-4357

ER -