E. S. Bartlett

The supergiant B[e] star LHA 115-S 18 – binary and/or luminous blue variable?

This research is partially supported by the Spanish Ministerio de Ciencia e Innovacion (MICINN) under grant AYA2010-21697-C05-01/05. The OGLE project has received funding from the European Research Council under the European Communitys Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. 246678 to AU. The AAT observations have been supported by the OPTICON project (observing proposals 2011A/014 and 2012A/015), which is funded by the European Commission under the Sevent Framework Programme (FP7).

The XMM–Newton survey of the Small Magellanic Cloud: XMMU J005011.2−730026 = SXP 214, a Be/X-ray binary pulsar★

In the course of the XMM―Newton survey of the Small Magellanic Cloud, a region to the east of the emission nebula N19 was observed in 2009 November. To search for new candidates for high-mass X-ray binaries, the EPIC-pn and EPIC-MOS data of the detected point sources were investigated and their spectral and temporal characteristics identified. A new transient (XMMU J005011.2-730026 = SXP 214) with a pulse period of 214.05 s was discovered; the source had a hard X-ray spectrum with a power-law index of ~0.65. The accurate X-ray source location permits the identification of the X-ray source with an ~15th magnitude Be star, thereby confirming this system as a new Be/X-ray binary.

The XMM-Newton survey of the Small Magellanic Cloud: discovery of the 11.866 s Be/X-ray binary pulsar XMMU J004814.0-732204(SXP11.87)

Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warsaw, PolandReceived 21 September 2010 / Accepted 6 November 2010ABSTRACTAims.One of the goals of the XMM-Newton survey of the Small Magellanic Cloud is the study of the Be/X-ray binary population.During one of our first survey observations a bright new trans ient − XMMUJ004814.0-732204− was discovered.Methods.We present the analysis of the EPIC X-ray data together with optical observations, to investigate the spectral and temporalcharacteristics of XMMUJ004814.0-732204.Results.We found coherent X-ray pulsations in the EPIC data with a period of (11.86642 ± 0.00017) s. The X-ray spectrum can bemodelled by an absorbed power-law with indication for a softexcess. Depending on the modelling of the soft X-ray spectrum, thephoton index ranges between 0.53 and 0.66. We identify the optical counterpart as a B = 14.9mag star which was monitored duringthe MACHO and OGLE-III projects. The optical light curves show regular outbursts by ∼0.5 mag in B and R and up to 0.9 mag in Iwhich repeat with a time scale of about 1000 days. The OGLE-III optical colours of the star are consistent with an early B spectraltype. An optical spectrum obtained at the 1.9m telescope of the South African Astronomical Observatory in December 2009 showsHα emission with an equivalent width of 3.5 ± 0.6A.Conclusions.The X-ray spectrum and the detection of pulsations suggest that XMMUJ004814.0-732204 is a new high mass X-raybinary pulsar in the SMC. The long term variability and the Hα emission line in the spectrum of the optical counterpart identify it asa Be/X-ray binary system.Key words. galaxies: individual: Small Magellanic Cloud – galaxies: stellar content – stars: emission-line, Be – stars: neutron –X-rays: binaries

Discovery of the neutron star spin and a possible orbital period from the Be/X-ray binary IGR J05414-6858 in the LMC

Context. The number of known Be/X-ray binaries in the Large Magellanic Cloud is small compared to the observed population of the Galaxy or the Small Magellanic Cloud. The discovery of a system in outburst provides the rare opportunity to measure its X-ray properties in detail. Aims. IGR J05414-6858 was discovered in 2010 with INTEGRAL and was found in another outburst with the Swift satellite in 2011. To characterise the system, we analysed the data from a follow-up XMM-Newton target of opportunity observation of the 2011 outburst and investigated the stellar counterpart with photometry and spectroscopy. Methods. We modelled the X-ray spectra from the EPIC instruments on XMM-Newton and compared them with Swift archival data. We searched for periodicities and variability in the X-ray and optical light curves. The optical counterpart was classified using spectroscopy obtained with ESO’s Faint Object Spectrograph at NTT. Results. The X-ray spectra as seen in 2011 are relatively hard with a photon index of ∼0.3−0.4 and show only low absorption. They deviate significantly from earlier spectra of a probable type-II outburst in 2010. The neutron star spin period of Pspin = 4.4208 s was discovered with EPIC-pn. The I-band light curve revealed a transition from a low to a high state around MJD 54 500. The optical counterpart is classified as B0-1 IIIe and shows Hα emission and a variable near-infrared excess that vanishes during the 2010 outburst. In the optical high state, we found a periodicity at 19.9 days, probably caused by binarity and indicating the orbital period.

Timing and spectral analysis of the unusual X-ray transient XTE J0421+560/CI Camelopardalis

We present a detailed X-ray study of the 2003 XMM‐Newton observation of the high-mass X-ray binary XTE J0421+560/CI Camelopardalis. The continuum of the X-ray spectrum is well described by a flat power law (� = 1.0 ± 0.2) with a large intrinsic absorbing column (NH = (4.4 ± 0.5) × 10 23 cm −2 ). We have decomposed the broad iron line into three separate components: Fe I-Kα ,F eI-Kβ and Fe XXIV-XXVKα. It is unclear how both neutral and almost fully ionized iron can exist simultaneously; however, we suggest that this could be evidence that the compact object is embedded in the circumstellar material. This does not appear to be consistent with the X-ray flux and spectrum of the source, which has remained essentially unchanged since the initial outburst. The iron abundance implied by the ratio of the neutral FeKα and Fe-Kβ is compatible with solar. We search for lags in the neutral Fe-Kα with respect to the continuum and find marginal evidence for a lag at ∼10 ks. We interpret this as the light crossing time of the torus which would suggest that the neutral iron is located at a radius of 10 au. This result depends on several assumptions including the distance to the system, the inclination, the mass of system and the orbital period, none of which are known with any great certainty. Better constraints on these system parameters and further observations of this system are required to confirm this result. We discuss the nature of this system in light of our results and place it in context with other binary B[e] stars.

XMM–Newton observation of the highly magnetized accreting pulsar Swift J045106.8−694803: evidence of a hot thermal excess

Several persistent, low-luminosity (LX ∼ 10 34 erg s −1 ), long-spin-period (P > 100 s) highmass X-ray binaries have been reported with blackbody components with temperatures > 1k eV. These hot thermal excesses have correspondingly small emitting regions ( 2 keV) and soft (< 2k eV) light curves is anticorrelated with the pulse profile. Simulations of the spectrum suggest that this is caused by the pulsations of the blackbody being ∼ π out of phase with those of the power-law component. Using a simple model for emission from hot spots on the neutron star surface, we fit the pulse profile of the blackbody component to obtain an indication of the geometry of the system.

Swift J053041.9-665426, a new Be/X-ray binary pulsar in the Large Magellanic Cloud ⋆

Aims. We observed the newly discovered X-ray source Swift J053041.9-665426 in the X-ray and optical regime to confirm its proposed nature as a high mass X-ray binary. Methods. We obtained XMM-Newton and Swift X-ray data, along with optical observations with the ESO Faint Object Spectrograph, to investigate the spectral and temporal characteristics o f Swift J053041.9-665426. Results. The XMM-Newton data show coherent X-ray pulsations with a period of 28.77521(10) s (1σ). The X-ray spectrum can be modelled by an absorbed power law with photon index within the range 0.76 to 0.87. The addition of a black body component increases the quality of the fit but also leads to strong depende nces of the photon index, black-body temperature and absorption column density. We identified the only optical counterpart within t he error circle of XMM-Newton at an angular distance of∼0.8 ′′ , which is 2MASS J05304215-6654303. We performed optical spectroscopy from which we classify the companion as a B0-1.5Ve star. Conclusions. The X-ray pulsations and long-term variability, as well as the properties of the optical counterpart, confirm that Swift J053041.9-665426 is a new Be/X-ray binary pulsar in the Large Magellanic Cloud.

The orbital solution and spectral classification of the high-mass X-ray binary IGR J01054−7253 in the Small Magellanic Cloud

We present X-ray and optical data on the Be/X-ray binary (BeXRB) pulsar IGR J 01054−7253 = SXP11.5 in the Small Magellanic Cloud (SMC). Rossi X-ray Timing Explorer (RXTE) observations of this source in a large X-ray outburst reveal an 11.483 ± 0.002 s pulse period and show both the accretion-driven spin-up of the neutron star and the motion of the neutron star around the companion through Doppler shifting of the spin period. Model fits to these data suggest an orbital period of 36.3 ± 0.4 d and u P of (4.7±0.3)×10 −10 seconds s −1 . We present an orbital solution for this system, making it one of the best-described BeXRB systems in the SMC. The observed pulse period, spin-up and X-ray luminosity of SXP11.5 in this outburst are found to agree with the predictions of neutron star accretion theory. Timing analysis of the long-term optical light curve reveals a periodicity of 36.70 ± 0.03 d, in agreement with the orbital period found from the model fit to the X-ray data. Using blue-end spectroscopic observations we determine the spectral type of the counterpart to be O9.5-B0 IV–V. This luminosity class is supported by the observed V-band magnitude. Using optical and near-infrared photometry and spectroscopy, we study the circumstellar environment of the counterpart in the months after the X-ray outburst.