X-ray observations of Be/X-ray binaries in the SMC

Abstract

Fifteen Be/X-ray binaries and candidates in the SMC were observed serendipitously with the EPIC instruments of XMM-Newton during two observations of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those sources are detected. For eleven of them an accurate position and in part detection of X-ray pulsations support the proposed identification as Be/X-ray binaries. In one case the improved X-ray position excludes the previously suggested identification with an Hα emission line star found within the ROSAT error circle. The detection of pulsations (172.2 s, 320.1 s and 751 s) from three hard X-ray sources with periods known from ASCA observations confirm their proposed identifications with ROSAT sources and their optical Be star counterparts. In addition, pulsations with a period of 263.6 s were found from XMMU J004723.7-731226 = RX J0047.3-7312. For SAX J0103.2-7209 a pulse period of 341.2±0.5 s was determined, continuing the large spin-up seen with ASCA, BeppoSAX and Chandra between 1996 and 1999 with a period derivative of -1.6 s yr^-1 covering now 4.5 years. The 0.3-10.0 keV EPIC spectra of all eleven Be/X-ray binaries and candidates are consistent with power-law energy distributions with derived photon indices strongly peaked at 1.00 with a standard deviation of 0.16. No pulsations are detected from RX J0049.2-7311 and RX J0049.5-7310 (both near the 9 s pulsar AX J0049-732) and RX J0105.1-7211 (near AX J0105-722, which may pulsate with 3.3 s), leaving the identification of the ASCA sources with ROSAT and corresponding XMM-Newton objects still unclear. We present an updated list of high-mass X-ray binaries (HMXBs) and candidates in the SMC incorporating improved X-ray positions obtained from Chandra and XMM-Newton observations. Including the results from this work and recent publications the SMC HMXB catalogue comprises 65 objects with at least 37 showing X-ray pulsations.

Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member states and the USA (NASA).