Suzaku broad-band spectrum of 4U 1705-44: probing the reflection component in the hard state

Tiziana Di Salvo, Rosario Iaria, Marco Matranga, Burderi, Ueda, Papitto, Riggio, Egron

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Abstract

Iron emission lines at 6.4-6.97 keV, identified with Kα radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disc radius is Rin = 17 ± 5Rg (where Rg is the gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.5 ± 0.5, the inclination angle with respect to the line of sight is i = 43° ± 5°, and the outer radius of the emitting region in the disc is Rout > 200Rg. We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ˜3 per cent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component.
Lingua originaleEnglish
pagine (da-a)2794-2802
Numero di pagine9
RivistaMonthly Notices of the Royal Astronomical Society
Volume449
Stato di pubblicazionePublished - 2015

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accretion
argon
broadband
radii
accretion disks
energy
iron
atoll
emissivity
probe
x rays
plasma
XMM-Newton telescope
newton
line of sight
neutron stars
inclination
luminosity
signatures
probes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cita questo

@article{781dab3f6cd047e08d0d91fa813841ad,
title = "Suzaku broad-band spectrum of 4U 1705-44: probing the reflection component in the hard state",
abstract = "Iron emission lines at 6.4-6.97 keV, identified with Kα radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disc radius is Rin = 17 ± 5Rg (where Rg is the gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.5 ± 0.5, the inclination angle with respect to the line of sight is i = 43° ± 5°, and the outer radius of the emitting region in the disc is Rout > 200Rg. We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ˜3 per cent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component.",
author = "{Di Salvo}, Tiziana and Rosario Iaria and Marco Matranga and Burderi and Ueda and Papitto and Riggio and Egron",
year = "2015",
language = "English",
volume = "449",
pages = "2794--2802",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",

}

TY - JOUR

T1 - Suzaku broad-band spectrum of 4U 1705-44: probing the reflection component in the hard state

AU - Di Salvo, Tiziana

AU - Iaria, Rosario

AU - Matranga, Marco

AU - Burderi, null

AU - Ueda, null

AU - Papitto, null

AU - Riggio, null

AU - Egron, null

PY - 2015

Y1 - 2015

N2 - Iron emission lines at 6.4-6.97 keV, identified with Kα radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disc radius is Rin = 17 ± 5Rg (where Rg is the gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.5 ± 0.5, the inclination angle with respect to the line of sight is i = 43° ± 5°, and the outer radius of the emitting region in the disc is Rout > 200Rg. We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ˜3 per cent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component.

AB - Iron emission lines at 6.4-6.97 keV, identified with Kα radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disc radius is Rin = 17 ± 5Rg (where Rg is the gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.5 ± 0.5, the inclination angle with respect to the line of sight is i = 43° ± 5°, and the outer radius of the emitting region in the disc is Rout > 200Rg. We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ˜3 per cent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component.

UR - http://hdl.handle.net/10447/154300

UR - http://mnras.oxfordjournals.org/content/449/3/2794

M3 - Article

VL - 449

SP - 2794

EP - 2802

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

ER -