Astron. Astrophys. 337, 772-778 (1998)

The discovery of 96 s pulsations from the variable X-ray source 1SAX J0544.1-710 in the Large Magellanic Cloud ^*

G. Cusumano ¹, G.L. Israel ^{** 2}, F. Mannucci ³, N. Masetti ⁴, T. Mineo ¹ and L. Nicastro <sup>1

1</sup> Istituto di Fisica Cosmica ed Applicazioni all' Informatica, CNR, Via U. La Malfa 153, I-90146 Palermo, Italy
² Osservatorio Astronomico di Roma , Via Frascati 33, I-00040 Monteporzio Catone (Roma), Italy
³ C.A.I.S.M.I. - CNR, Largo E. Fermi 5, I-50125 Firenze, Italy
⁴ Istituto Tecnologie e Studio Radiazione Extraterrestre, CNR, Via Gobetti 101, I-40129 Bologna, Italy

Received 13 May 1998 / Accepted 22 June 1998

Abstract

We report the discovery of a s period X-ray pulsar in the direction of the Large Magellanic Cloud (LMC). The Beppo SAX X-ray spectrum is well fitted by an absorbed power-law model with photon index . The unabsorbed luminosity in the 2-10 keV energy range is erg s^-1. The Beppo SAX position ( uncertainty radius) of 1SAX J0544.1-710 was found to be consistent with that of the ASCA source AX J0448-70.4 and WGACAT (ROSAT PSPC) source 1WGA J0544.1-710. The source was detected four times between 1991 and 1996 at luminosity levels from to erg s^-1 (2-10 keV), while during a relatively deep ROSAT HRI observation an extrapolated 2-10 keV luminosity upper limit of erg s^-1 was obtained. Timing analysis of the ASCA data confirmed the Beppo SAX period discovery. Long-term flux variability is evident in the ROSAT and Einstein data. We revealed a pronounced H activity from a bright () likely Be-type star within the ROSAT PSPC error circle. Its optical spectrum shows it is located in the LMC. These results strongly suggest that 1SAX J0544.1-710 is a transient X-ray pulsar in a massive binary system.

Key words: stars: emission-line, Be stars: neutron pulsars: individual: 1SAX J0544.1-710 galaxies: Magellanic clouds X-rays: stars

* Partially based on data collected with the ESO telescopes in La Silla
** Affiliated to I.C.R.A.

Send offprint requests to: cusumano@ifcai.pa.cnr.it

SIMBAD Objects

Contents

• 1. Introduction
• 2. Beppo SAX observation
  • 2.1. Timing analysis
  • 2.2. Spectral analysis
• 3. Previous X-ray observations
  • 3.1. ASCA GIS
  • 3.2. ROSAT PSPC and HRI
  • 3.3. Einstein IPC
• 4. Optical observations
• 5. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: August 27, 1998
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