The incompatibility of rapid rotation with narrow photospheric X-ray lines in EXO 0748-676

Jinrong Lin, Feryal Ozel, Deepto Chakrabarty, Dimitrios Psaltis

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

X-ray observations of EXO 0748-676 during thermonuclear bursts revealed a set of narrow (Δλ/λ = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15% rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.

Original languageEnglish (US)
Pages (from-to)1053-1056
Number of pages4
JournalAstrophysical Journal
Volume723
Issue number2
DOIs
StatePublished - Nov 10 2010

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incompatibility
neutron stars
oscillation
oscillations
x rays
bursts
photosphere
emerging
radii

Keywords

  • Stars: individual (EXO 0748-676)
  • Stars: neutron
  • X-rays: binaries

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

The incompatibility of rapid rotation with narrow photospheric X-ray lines in EXO 0748-676. / Lin, Jinrong; Ozel, Feryal; Chakrabarty, Deepto; Psaltis, Dimitrios.

In: Astrophysical Journal, Vol. 723, No. 2, 10.11.2010, p. 1053-1056.

Research output: Contribution to journalArticle

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abstract = "X-ray observations of EXO 0748-676 during thermonuclear bursts revealed a set of narrow (Δλ/λ = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15{\%} rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.",
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AU - Chakrabarty, Deepto

AU - Psaltis, Dimitrios

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N2 - X-ray observations of EXO 0748-676 during thermonuclear bursts revealed a set of narrow (Δλ/λ = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15% rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.

AB - X-ray observations of EXO 0748-676 during thermonuclear bursts revealed a set of narrow (Δλ/λ = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15% rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.

KW - Stars: individual (EXO 0748-676)

KW - Stars: neutron

KW - X-rays: binaries

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