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

Tiziana Di Salvo, Degenaar, Paerels, Bachetti, Michael L. Parker, Bostrom, Ludlam, Tomsick, Natalucci, Didier Barret, Jon M. Miller, Edward M. Cackett

Risultato della ricerca: Article

18 Citazioni (Scopus)

Abstract

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.
Lingua originaleEnglish
Numero di pagine12
RivistaTHE ASTROPHYSICAL JOURNAL
Volume836
Stato di pubblicazionePublished - 2017

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circular orbits
accretion disks
neutron stars
accretion
equation of state
radii
magnetosphere
boundary layer
magnetic field
modeling
magnetospheres
systematic errors
boundary layers
equations of state
parameter
magnetic fields

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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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.

In: THE ASTROPHYSICAL JOURNAL, Vol. 836, 2017.

Risultato della ricerca: Article

Di Salvo, T, Degenaar, Paerels, Bachetti, Parker, ML, Bostrom, Ludlam, Tomsick, Natalucci, Barret, D, Miller, JM & Cackett, EM 2017, 'A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with NuStar', THE ASTROPHYSICAL JOURNAL, vol. 836.
Di Salvo, Tiziana ; Degenaar ; Paerels ; Bachetti ; Parker, Michael L. ; Bostrom ; Ludlam ; Tomsick ; Natalucci ; Barret, Didier ; Miller, Jon M. ; Cackett, Edward M. / A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with NuStar. In: THE ASTROPHYSICAL JOURNAL. 2017 ; Vol. 836.
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abstract = "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.",
author = "{Di Salvo}, Tiziana and Degenaar and Paerels and Bachetti and Parker, {Michael L.} and Bostrom and Ludlam and Tomsick and Natalucci and Didier Barret and Miller, {Jon M.} and Cackett, {Edward M.}",
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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 -