Jose Luis Galache

A Long Look at the Be/X-Ray Binaries of the Small Magellanic Cloud

We have monitored 41 Be/X-ray binary systems in the Small Magellanic Cloud over ~9 yr using PCA RXTE data from a weekly survey program. The resulting light curves were analyzed 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, SXP 46.4, SXP 89.0, and SXP 165, were found to be misidentifications of SXP 46.6, SXP 91.1, and SXP 169, respectively.

X-ray and Radio Variability of M31*, The Andromeda Galaxy Nuclear Supermassive Black Hole

We confirm our earlier tentative detection of M31* in X-rays and measure its light curve and spectrum. Observations in 2004-2005 find M31* rather quiescent in the X-ray and radio. However, X-ray observations in 2006-2007 show M31* to be highly variable at times. A separate variable X-ray source is found near P1, the brighter of the two optical nuclei. The apparent angular Bondi radius of M31* is the largest of any black hole and large enough to be well resolved with Chandra. The diffuse emission within this Bondi radius is found to have an X-ray temperature ~0.3 keV and density 0.1 cm–3, indistinguishable from the hot gas in the surrounding regions of the bulge given the statistics allowed by the current observations. The X-ray source at the location of M31* is consistent with a point source and a power-law spectrum with energy slope 0.9 ± 0.2. Our identification of this X-ray source with M31* is based solely on positional coincidence.

The Chandra Small Magellanic Cloud Wing Survey - the search for X-ray Binaries

We have detected 523 sources in a survey of the Small Magellanic Cloud (SMC) Wing with Chandra. By cross-correlating the X-ray data with optical and near-infrared catalogues we have found 300 matches. Using a technique that combines X-ray colours and X-ray to optical flux ratios we have been able to assign preliminary classifications to 265 of the objects. Our identifications include four pulsars, one high-mass X-ray binary (HMXB) candidate, 34 stars and 185 active galactic nuclei (AGNs). In addition, we have classified 32 sources as ’hard’ AGNs which are likely absorbed by local gas and dust, and nine ’soft’ AGNs whose nature is still unclear. Considering the abundance of HMXBs discovered so far in the Bar of the SMC the number that we have detected in the Wing is low.

X-ray bright sources in the Chandra Small Magellanic Cloud Wing Survey – detection of two new pulsars

ABSTRACT We investigate the X-ray and optical properties of a sample of X-ray bright sourcesfrom the Small Magellanic Cloud (SMC) Wing Survey. We have detected two newpulsars with pulse periods of 65.8 s (CXOU J010712.6-723533) and 700 s (CXOUJ010206.6-714115), and present observations of two previously known pulsars RXJ0057.3-7325 (SXP101) and SAX J0103.2-7209 (SXP348). Our analysis has led tothree new optical identifications for the detected pulsars. We find long-term opticalperiods for two of the pulsars, CXOU J010206.6-714115 and SXP101, of 267 and 21.9d, respectively. Spectral analysis of a sub-set of the sample shows that the pulsarshave harder spectra than the other sources detected. By employing a quantile-basedcolour-colour analysis we are able to separate the detected pulsars from the rest ofthe sample. Using archival catalogues we have been able to identify counterparts forthe majority of the sources in our sample. Combining this with our results from thetemporal analysis of the Chandra data and archival optical data, the X-ray spectralanalysis, and by determining the X-ray to optical flux ratios we present preliminaryclassifications for the sources. In addition to the four detected pulsars, our sampleincludes two candidate foreground stars, 12 probable active galactic nuclei, and fiveunclassified sources.Keywords: X-rays:binaries– stars:emission-line,Be – (galaxies:)MagellanicClouds

Optical and X-ray variability of two Small Magellanic Cloud X-ray binary pulsars - SXP46.6 and SXP6.85

We present long-term optical and RXTE data of two X-ray binary pulsars in the Small Magellanic Cloud, SXP46.6 and SXP6.85. The optical light curves of both sources show substantial (?0.5-0.8 mag) changes over the time-span of the observations. While the optical data for SXP6.85 do not reveal any periodic behaviour, by detrending the optical measurements for SXP46.6 we find an orbital period of ?137 d, consistent with results from the X-ray data. The detection of Type I X-ray outbursts from SXP46.6, combined with the fact that we also see optical outbursts at these times, implies that SXP46.6 is a high orbital eccentricity system. Using contemporaneous optical spectra of SXP46.6, we find that the equivalent width of the Ha emission line changes over time indicating that the size of the circumstellar disc varies. By studying the history of the colour variations for SXP6.85, we find that the source gets redder as it brightens which can also be attributed to changes in the circumstellar disc. We do not find any correlation between the X-ray and optical data for SXP6.85. The results for SXP6.85 suggest that it is a low-eccentricity binary and that the optical modulations are due to the Be phenomenon.

Now you see it, now you don't – the circumstellar disc in the GRO J1008−57 system

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.

INTEGRAL deep observations of the Small Magellanic Cloud

Deep observations of the Small Magellanic Cloud (SMC) and region were carried out in the hard X-ray band by the INTEGRAL observatory in 2008-2009. The field of view of the instrument permitted simultaneous coverage of the entire SMC and the eastern end of the Magellanic Bridge. In total, INTEGRAL detected seven sources in the SMC and five in the Magellanic Bridge; the majority of the sources were previously unknown systems. Several of the new sources were detected undergoing bright X- ray outbursts and all the sources exhibited transient behaviour except the supergiant system SMC X-1. They are all thought to be High Mass X-ray Binary (HMXB) systems in which the compact object is a neutron star.

High-mass X-ray binary SXP18.3 undergoes the longest type II outburst ever seen in the Small Magellanic Cloud

On 2006 August 30, SXP18.3 a high-mass X-ray binary (HMXB) in the Small Magellanic Cloud (SMC) with an 18.3 s pulse period was observed by Rossi X-ray Timing Explorer (RXTE). The source was seen continuously for the following 36 weeks. This is the longest type II outburst ever seen from a HMXB in the SMC. During the outburst, SXP18.3 was located from serendipitous XMM–Newton observations. The identification of the optical counterpart has allowed SXP18.3 to be classified as a Be/X-ray binary. This paper will report on the analysis of the optical and weekly RXTE X-ray data that span the last 10 yr. The extreme length of this outburst has for the first time enabled us to perform an extensive study of the pulse timing of a SMC Be/X-ray binary. We present a possible full orbital solution from the pulse timing data. An orbital period of 17.79 d is proposed from the analysis of the Optical Gravitational Lensing Experiment (OGLE) III light curve placing SXP18.3 on the boundary of known sources in the Corbet diagram.

An optical and X-ray study of the counterpart to the Small Magellanic Cloud X-ray binary pulsar system SXP327

Optical and X-ray observations are presented here of a newly reported X-ray transient system in the Small Magellanic Cloud. The data reveal many previously unknown X-ray detections of this system and clear evidence for a 45.99 d binary period. In addition, the optical photometry shows recurring outburst features at the binary period which may be well indicative of the neutron star interacting with a circumstellar disc around a Be star.

Optical follow‐up of new Small Magellanic Cloud wing Be/X‐ray binaries

ABSTRACT We investigate the optical counterparts of recently discovered Be/X-ray binaries in the SmallMagellanic Cloud. In total four sources, SXP101, SXP700, SXP348 and SXP65.8 were de-tected during the Chandra Survey of the Wing of the SMC. SXP700 and SXP65.8 were pre-viously unknown. Many optical ground based telescopes have been utilised in the opticalfollow-up, providing coverage in both the red and blue bands. This has led to the classifica-tionof all ofthe counterpartsas Be stars andconfirmsthat th ree lie within the Galactic spectraldistribution of known Be/X-ray binaries. SXP101 lies outside this distribution becoming thelatest spectral type known. Monitoring of the Hα emission line suggests that all the sourcesbar SXP700 have highly variable circumstellar disks, possibly a result of their comparativelyshortorbitalperiods.Phase resolvedX-rayspectroscopyhas alsobeenperformedonSXP65.8,revealing that the emission is indeed harder during the passage of the X-ray beam through theline of sight.Key words: X-rays: binaries - stars: emission-line, Be - Magellanic Clouds.