X-ray binary systems in the Small Magellanic Cloud

We present the result of a systematic search for spectrally hard and soft X-ray binary systems in the Small Magellanic Cloud (SMC). This search has been applied to ROSAT PSPC data (0.1-2.4 keV) collected during nine pointed observations towards this galaxy covering a time span of similar to 2 years from October 91 till October 93. Strict selection criteria have been defined in order to confine the sample of candidates. Finally seven spectrally hard and four spectrally soft sources were selected from the list as candidates for binaries in the SMC. The sample is luminosity limited (above similar to 3 x 10(35) erg s(-1)). SMC X-1 has been observed during a full binary orbit starting with a low-state covering an X-ray eclipse and emerging into a bright long-duration flare with two short-duration flares separated by similar to 10 hours. The Be type transient SMC X-2 has been redetected by ROSAT (second reported outburst). Variability has been found in the X-ray source RX J0051.8-7231 already discovered with Einstein and in RX J0052.1-7319 which is also known from Einstein observations. RX J0101.0-7206 has been discovered at the north-eastern boundary of the giant SMC HII region N66 during an X-ray outburst and half a year later during a quiescent phase. A variable source, RX J0049.1-7250, located north-east of the SMC supernova remnant N 19 and which may either be an X-ray binary or an AGN turns out to be strongly absorbed. It may be located behind the SMC. If it is an X-ray binary then it radiates at the Eddington limit in the X-ray bright state. Another variable and hard X-ray source RX J0032.9-7348 has been discovered at the south-eastern border of the body of the SMC. A high mass X-ray binary nature is favored for this source. A high mass X-ray binary nature is favored for the persistent sources where an optical counterpart of spectral type O or B has been identified. A possible Be type nature is favored for the few transient X-ray sources for which an optical identification with a B star has been achieved. We find about equal numbers of persistent (and highly variable) and transient X-ray binaries and binary candidates. Sources for which no optical candidate has been found in catalogs are candidate low-mass X-ray binaries (LMXBs) or black hole binaries. We searched for CAL 87 like systems in the SMC pointed catalog and found none. This implies that these systems are very rare and currently not existent in the SMC. A new candidate supersoft source RX J0103.8-7254 has been detected. We cannot exclude that it is a foreground object.