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


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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 1

1 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 [FORMULA] 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 [FORMULA]. The unabsorbed luminosity in the 2-10 keV energy range is [FORMULA] erg s-1. The Beppo SAX position ([FORMULA] 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 [FORMULA] to [FORMULA] erg s-1 (2-10 keV), while during a relatively deep ROSAT HRI observation an extrapolated 2-10 keV luminosity upper limit of [FORMULA] 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[FORMULA] activity from a bright ([FORMULA]) likely Be-type star within the [FORMULA] 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

© European Southern Observatory (ESO) 1998

Online publication: August 27, 1998

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