This work represent the first major study of the optical and infrared characteristics of the mass donor companions to the X‐ray pulsars in the Small Magellanic Cloud (SMC). In this work several new counterparts have been identified, and possible ones confirmed, as companions to X‐ray pulsars in the SMC giving a total of 34 such objects now identified. In addition this work presents three new binary periods and confirms two X‐ray periods using optical data for objects in this group. This homogeneous sample has been studied as a group to determine important general characteristics that may offer an insight into the evolution of such systems. In particular, the spectral class distribution shows a much greater agreement with those of isolated Be stars, and appears to be in some disagreement with the galactic population of Be stars in Be/X‐ray binaries. Studies of the long‐term optical modulation of the Be star companions reveal an extremely variable group of objects, a fact which will almost certainly make a major contribution to the pronounced X‐ray variability. The spatial distribution of these systems within the SMC is investigated and strongly suggests a link between massive star formation and the H i density distribution. Finally, studies of the circumstellar disc characteristics reveal a strong link with optical variability offering important clues into the long‐term stability of such discs.

-We have monitored 41 Be/X-ray binary systems in the Small Magellanic Cloud over ∼ 9 years using PCA-RXTE data from a weekly survey program. The resulting light curves were analysed in search of orbital modulations with the result that 10 known orbital ephemerides were confirmed and refined, while 10 new ones where determined. A large number of X-ray orbital profiles are presented for the first time, showing similar characteristics over a wide range of orbital periods. Lastly, three pulsars: SXP46.4, SXP89.0 and SXP165 were found to be misidentifications of SXP46.6, SXP91.1 and SXP169, respectively. Subject headings: galaxies: individual (Small Magellanic Cloud) -pulsars: general -X-rays: binaries Fig. 6.-SXP6.85. a) Top: X-ray amplitude light curve. b) Middle: Lomb-Scargle power

In 2005 May/June, after 10 yr of inactivity, the Be/X-ray binary system A 0535+26 underwent a major X-ray outburst. In this paper, data are presented from 10 yr of optical, infrared and X-ray monitoring showing the behaviour of the system during the quiescent epoch and the lead up to the new outburst. The results show the system going through a period when the Be star in the system had a minimal circumstellar disc and then a dramatic disc recovery leading, presumably, to the latest flare up of X-ray emission. The data are interpreted in terms of the state of the disc and its interaction with the neutron star companion.

Abstract. We report the association of the INTEGRAL source IGR J18027-2016 with the BeppoSAX source SAX J1802.7-2017. IGR J18027-2016 is seen to be a weak, persistent source by the IBIS/ISGRI instrument on board INTEGRAL with an average source count rate of 0.58 counts s −1 (∼6.4 mCrab) in the 20−40 keV band. Timing analysis performed on the ISGRI data identifies an orbital period of of 4.5696 ± 0.0009 days and gives an ephemeris of mid-eclipse as, T mid = 52 931.37 ± 0.04 MJD. Re-analysis of archival BeppoSAX data has provided a mass function for the donor star, f (m) = 16 ± 1 M and a projected semimajor axis of a x sin i = 68 ± 1 lt-s. We conclude that the donor is an OB-supergiant with a mass of 18.8−29.3 M and a radius of 15.0−23.4 R . Spectra obtained by XMM-Newton and ISGRI indicate a high hydrogen column density of N H = 6.8 × 10 22 cm −2 , which suggests intrinsic absorption. The source appears to be a high mass X-ray binary with the neutron star emitting X-rays through wind-fed accretion while in an eclipsing orbit around an OB-supergiant.

Multiwavelength observations are reported here of the Be/X‐ray binary pulsar system GRO J1008−57. Over ten years worth of data are gathered together to show that the periodic X‐ray outbursts are dependant on both the binary motion and the size of the circumstellar disc. In the first instance an accurate orbital solution is determined from pulse periods, and in the second case the strength and shape of the Hα emission line is shown to be a valuable indicator of disc size and its behaviour. Furthermore, the shape of the emission line permits a direct determination of the disc size which is in good agreement with theoretical estimates. A detailed study of the pulse period variations during outbursts determined the binary period to be 247.8 ± 0.4 d, in good agreement with the period determined from the recurrence of the outbursts.