Astron. Astrophys. 346, 453-458 (1999)

A BeppoSAX observation of the supersoft source 1E 0035.4-7230

P. Kahabka ¹, A.N. Parmar ² and H.W. Hartmann <sup>3

1</sup> Astronomical Institute and Center for High Energy Astrophysics, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
² Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
³ SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Received 17 February 1999 / Accepted 25 March 1999

Abstract

Results from a 37 ks BeppoSAX Low-Energy Concentrator Spectrometer (LECS) observation of the supersoft source SMC 13 (=1E 0035.4-7230) in the Small Magellanic Cloud are reported. This source has probably the softest spectrum observed so far with BeppoSAX, with no detected counts 0.5 keV. The BeppoSAX spectrum is fitted either with a blackbody spectrum with an effective temperature kT = 26-58 eV, an LTE white dwarf atmosphere spectrum with kT = 35-50 eV, or a non-LTE white dwarf atmosphere spectrum with kT = 25-32 eV. The bolometric luminosity is not very well constrained, it is and for the LTE and the non-LTE spectrum (90% confidence).

We also applied a spectral fit to combined spectra obtained with BeppoSAX LECS and with ROSAT PSPC. We find that a blackbody spectrum with an effective temperature kT=(39-47) eV and a bolometric luminosity of fits the data. The data are also fitted with a blackbody with a kT of (50-81) eV, an average C-edge at (0.38-0.47) keV with an optical depth , and a bolometric luminosity of (90% confidence). We also applied LTE and non-LTE white dwarf atmosphere spectra. The kT derived for the LTE spectrum is (45-49) eV, the bolometric luminosity is , The kT derived for the non-LTE spectrum is (27-29) eV, the bolometric luminosity is . We can exclude any spectrally hard component with a luminosity of more than (for a bremmsstrahlung with a temperature of 0.5 keV) at a distance of 60 kpc. The LTE temperature is therefore in the range  K and the non-LTE temperature in the range  K.

Assuming the source is on the stability line for atmospheric nuclear burning, we constrain the white dwarf mass from the LTE and the non-LTE fit to 1.1  and 0.9  respectively. However, the temperature and luminosity derived with the non-LTE model for 1E 0035.4-7230 is consistent with a lower mass () white dwarf as predicted by Sion & Starrfield (1994). At the moment, neither of these two alternatives for the white dwarf mass can be excluded.

Key words: accretion, accretion disks stars: binaries: close stars: individual: 1E 0035.4-7230 stars: white dwarfs X-rays: stars

Send offprint requests to: ptk@astro.uva.nl

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observation
• 3. BeppoSAX spectral fit
  • 3.1. Blackbody spectral fits
  • 3.2. WD atmosphere spectral fits
• 4. Combined BeppoSAX and ROSAT PSPC spectral fits
  • 4.1. Blackbody spectral fits
  • 4.2. WD atmosphere spectral fits
• 5. Discussion
  • 5.1. Constraints inferred from the Saha equation
  • 5.2. The evolutionary state of 1E 0035.4-7230
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999
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