The polar cap structure of the X-ray pulsar 4U 1538-52

T. Bulik, Peter Istvan Meszaros, J. W. Woo, F. Nagase, K. Makishima

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

We have compared the pulse phase-dependent spectral observations of 4U 1538-52 obtained from Ginga to a series of static model atmospheres of curved accreting polar caps, utilizing a magnetized radiative transfer code with relativistic polarized cross sections. A χ2 fit was performed on the symmetrized pulse shapes, allowing the parameters of the two polar caps to vary independently. We find evidence for a significant difference between the caps, both in terms of opening angle and temperature, while the optical depth is similar and compatible with radiative deceleration models. The polar caps appear larger than what is usually estimated from dipole fields, and are not located at the antipodes of each other. A broader distribution of magnetic fields is required than expected from a dipolar field at constant radius. If the magnetic field is indeed dipolar, it should be off-center in respect to the star and the accretion shock height exhibits an unusual dependence on the polar angle. An alternative possibility is that the magnetic field is disordered on scales small compared to the polar cap radius.

Original languageEnglish (US)
Pages (from-to)564-574
Number of pages11
JournalAstrophysical Journal
Volume395
Issue number2
DOIs
StatePublished - Aug 20 1992

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polar caps
pulsars
magnetic field
x rays
antipodes
magnetic fields
static models
optical depth
radii
radiative transfer
deceleration
cross section
pulses
accretion
caps
optical thickness
atmosphere
shock
dipoles
atmospheres

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Bulik, T., Meszaros, P. I., Woo, J. W., Nagase, F., & Makishima, K. (1992). The polar cap structure of the X-ray pulsar 4U 1538-52. Astrophysical Journal, 395(2), 564-574. https://doi.org/10.1086/171676
Bulik, T. ; Meszaros, Peter Istvan ; Woo, J. W. ; Nagase, F. ; Makishima, K. / The polar cap structure of the X-ray pulsar 4U 1538-52. In: Astrophysical Journal. 1992 ; Vol. 395, No. 2. pp. 564-574.
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Bulik, T, Meszaros, PI, Woo, JW, Nagase, F & Makishima, K 1992, 'The polar cap structure of the X-ray pulsar 4U 1538-52', Astrophysical Journal, vol. 395, no. 2, pp. 564-574. https://doi.org/10.1086/171676

The polar cap structure of the X-ray pulsar 4U 1538-52. / Bulik, T.; Meszaros, Peter Istvan; Woo, J. W.; Nagase, F.; Makishima, K.

In: Astrophysical Journal, Vol. 395, No. 2, 20.08.1992, p. 564-574.

Research output: Contribution to journalArticle

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Bulik T, Meszaros PI, Woo JW, Nagase F, Makishima K. The polar cap structure of the X-ray pulsar 4U 1538-52. Astrophysical Journal. 1992 Aug 20;395(2):564-574. https://doi.org/10.1086/171676