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Astron. Astrophys. 334, L65-L68 (1998)

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1. Introduction

On 1998 January 20 during a R XTE observation in the direction of the Small Magellanic Cloud (SMC), a previously unknown X-ray source, namely XTE J0055-724, was detected at a flux level (2-10 keV) of [FORMULA] 6.0 [FORMULA] 10-11 erg s-1 cm-2. The source showed pulsations at a period of [FORMULA] 59 s (Marshall & Lochner, 1998a). A previous R XTE observation of the same field performed on 1998 January 12 failed to detect the source.

In response to these findings, simultaneous Beppo SAX and R XTE observations of a region including the R XTE error circle ([FORMULA] radius) of XTE J0055-724, were carried out on 1998 Jannuary 28. The results of these observations are reported elsewhere (Santangelo et al. 1998a; Marshall et al. 1998b). Thanks to the spatial capabilities of the imaging X-ray concentrators on board Beppo SAX, an improved position ([FORMULA] radius) was obtained for the pulsating source, named 1SAX J0054.9-7226 (Santangelo et al. 1998a,b). The new Beppo SAX error circle contains only the previously classified ROSAT and Einstein X-ray sources 1WGA J0054.9-7226 and 2E 0053.2-7242, which are likely the same source. In the following we adopt the earliest source name, i.e. Einstein 's. 2E 0053.2-7242 is a variable X-ray source in the SMC, which was already considered a candidate High Mass X-ray Binary by Wang & Wu (1992; source #35), Bruhweiler et al. (1987; source # 9) and by White et al. (1994; in the WGACAT), based on its high spectral hardness.

We report in this letter on the results from the analysis of the Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) observations from the ROSAT public archive.

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© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998