Astron. Astrophys. 353, 129-134 (2000)

1. Introduction

Recently, Yokogawa & Koyama (1998) reported a new ASCA X-ray pulsar in the SMC named as AX J0105-722 with a pulse period of 3.343000.00003 s (observations made on 21-23 May 1996) from a source at RA(J2000)=1^h05^m06^s and Dec(J2000)= -72^o 11´ 08". The positional error from their observations is estimated to be 1´ (at 90% confidence) and a power-law X-ray spectrum with photon index 2.20.3 was derived.

This SMC region has been surveyed at H wavelengths by Davies et al. (1976) which named this region as DEM S128 and classified it as a faint and diffuse H II region with diameter of 1.´5  1.´2. Bica & Schmitt (1995) also classified DEM S128 using the ESO/SERC R and J Sky Survey as a H II region with embedded association and diameter of 1.´6  1.´3 (position angle = 40^o).

The first X-ray sources in this region were reported from the Einstein satellite observations. Inoue et al. (1983) detected the X-ray source (IKT 24) and due to positional coincidence (within the X-ray positional error) with DEM S128 they classified this source as a supernova remnant (SNR). The source is also included (without classification) in the Einstein SMC catalogues of Bruhweiler et al. (1987) and Wang & Wu (1992) as BKGS 14 and WW 53, respectively.

The only nearby X-ray source from the ROSAT PSPC catalogue of Kahabka et al. (1999), RX J0105.3-7210 (source 191) shows X-ray extent suggesting an SNR identification with DEM S128. Filipovic et al. (1998a) found that the Parkes radio source SMC B0104-7226 coincides with the X-ray source and because of H emission this source was classified as SNR. However, in the ROSAT observations analyzed by Kahabka et al. (1999), RX J0105.3-7210 was detected at an off-axis angle of 23´ where the ROSAT resolution is already degraded and several sources may contribute to its emission.

Schwering & Israel (1989) detected the IRAS source LI SMC 170 which was identified as the counterpart to the radio source SMC B0104-7226 (Filipovi et al. 1997, 1998b). However, no other SNR criteria were applied to confirm the nature of this object. Also, this region was surveyed with the MOST radio telescope at 843 MHz (Turtle et al. 1998; Amy & Ball 1993). For more details of all these earlier observations see Table 1.

Table 1. Details of previous observations of the region near AX J0105-722.

Recently, Haberl et al. (1999) produced an improved catalogue based on the complete set of ROSAT PSPC pointed data of the SMC. It includes in particular an observation centered only 5´ from AX J0105-722 which was not analyzed by Kahabka et al. (1999) and allowed a survey of the area with good resolution. The catalogue contains six sources in the vicinity of the ASCA source indicating the complexity of X-ray emission in that area. Here, we present new results from ROSAT PSPC X-ray, Australia Telescope Compact Array (ATCA) radio-continuum and CTIO optical studies of the region around AX J0105-722 in order to identify its counterpart and confirm the SNR nature of DEM S128.

© European Southern Observatory (ESO) 2000

Online publication: December 8, 1999
helpdesk.link@springer.de