The original idea for this IAU Symposium arose from realizing that present-day X-ray satellites, XMM-Newton and Chandra, are now allowing us to conduct studies of individual X-ray sources in other galaxies, much like this was until recently mostly confined to sources in our own Galaxy and in the Magellanic Clouds. In addition, $\gamma$-ray astronomy is catching up as it were, now being able to study well-defined sources in our own Galaxy with the INTEGRAL satellite, and also the highest-energy sources accessible, at TeV, with the newly constructed Cherenkov receiver array(s).

The proliferation of X-ray astronomy missions over the last 10 years has had a major impact on our knowledge of Galactic X-ray binaries. More recently, Chandra and XMM-Newton have provided a dramatically improved census of extra-galactic X-ray binaries. In this talk I will provide an overview of the various populations and observational properties of X-ray binaries in our Galaxy, in an effort to “set the scene” for a comparison with their extra-galactic counterparts.

This paper discusses several aspects of current research on high energy emission from supernova remnants, covering the following main topics: 1) The recent evidence for magnetic field amplification near supernova remnant shocks, which makes that cosmic rays are more efficiently accelerated than previously thought. 2) The evidence that ions and electrons in some remnants have very different temperatures, and only equilibrate through Coulomb interactions. 3) The evidence that the explosion that created Cas A was asymmetric, and seems to have involved a jet/counter jet structure. And finally, 4), I will argue that the unremarkable properties of supernova remnants associated with magnetar candidates, suggest that magnetars are not formed from rapidly ($P\approx 1$ ms) rotating proto-neutron stars. It is therefore more likely that they are formed from massive progenitor stars with high magnetic fields.

We have discovered a number of nonthermal X-ray features within central 40 pc region of the Galactic center by analysing 600-ksec observations of Chandra archival data. Most of the detected X-ray structures exhibit small-scale knot-like morphologies and their spectra are well reproduced by single hard power-law with photon indices of 1-2. Among them, the most outstanding features are the three X-ray knots which are aligned on a straight line from the potition of Sgr A* to north-northwest direction. The X-ray properties of these knots lead us to suspect that they are X-ray jets ejected from Sgr A* in the recent past. In addition, we have obtained an indication that the summed flux of nonthermal diffuse X-rays within 30 pc of the GC seems to be smoothly connected to the 20-100 keV flux detected with INTEGRAL IBIS/ISGRI. These results suggest that the origin of GC hard X-rays (or High energy Gamma-rays) is not (or partly) from the Galactic nucleus.

It is discovered that young SNRs have very thin filaments emitting nonthermal X-rays from accelerated electrons. In this paper, a new age and distance indicator is proposed using the spectral and spatial features of nonthermal filaments. We applied this method to the Vela Jr. SNR, for which age and distance are still unknown, and estimated that this SNR is one of the nearest and youngest SNR in our Galaxy: the estimated distance and age are 0.33 (0.26–0.50) kpc and 660 (420–1400) years, respectively.

We report on an XMM-Newton observation of the supernova remnant (SNR) DEM L241 in the Large Magellanic Cloud. In the soft band image, the emission shows an elongated structure, like a killifish (Head and Tail), with a central point source, named as XMMU J053559.3–673509 (Eye). The Eye's spectrum is well reproduced with a power-law model. The source has neither significant coherent pulsations nor time variabilities. Its luminosity and spectrum remind us that the source might be a pulsar and/or pulsar wind nebula in DEM L241. The spectra of Head and Tail are well reproduced by a non-equilibrium ionization plasma model with over-abundant Ne and under-abundant Fe, suggesting that the progenitor of DEM L241 is a very massive star.

We report on analysis of the poorly studied source 2RXP J130159.6-635806 at different epochs with ASCA, BeppoSAX, XMM-Newton and INTEGRAL. The source shows coherent X-ray pulsations at a period ${\sim}700$ s with $\dot{\nu}\sim 2\times 10^{-13}$ Hz s$^{-1}$. A broad band (1–60 keV) spectral analysis of 2RXP J130159.6-635806 based on almost simultaneous XMM-Newton and INTEGRAL data demonstrates that the source spectrum is an absorbed power law with a photon index $\Gamma\sim 0.5-1.0$ and a cut-off energy of ${\sim}25$ keV. We also report on the identification of the likely infrared counterpart to 2RXP J130159.6-635806. The interstellar reddening does not allow us to strongly constrain the spectral type of the counterpart. The latter is, however, consistent with a Be star, the kind of which is often observed in accretion powered X-ray pulsars.

Very massive stars (${\gtrsim} 20$ M$_{\odot}$) are rare but important components of galaxies. Products of core nucleosynthesis from these stars are distributed into the circumstellar environment via wind-driven mass loss. Explosive nucleosynthesis after core collapse further enriches the galactic medium. Clusters of such stars can produce galactic chimneys which can pierce the galactic disk and chemically enrich intergalactic space. Such processes are vitally important to the chemical evolution of the early Universe, when the stellar mass function was much more weighted to massive stars.

Very massive stars are difficult to study, since they are formed in distant clusters which yield problems of sensitivity and source crowding. A relatively new tool for studying these systems is via high spatial, spectral and temporal resolution observations in the X-ray band. In this note we describe some recent progress in studying mechanisms by which very massive stars produce X-ray emission.

The conventional picture of disk accretion onto magnetized neutron stars has been challenged by the spin changes observed in a few X-ray pulsars, and by theoretical results from numerical simulations of disk-magnetized star interactions. Here we present a model for the torque exerted by accretion disks on magnetized neutron stars, assuming accretion continues even for fast rotators.

We report on astrophysical aspects of fully innovative very wide–field X-ray telescopes with high sensitivity. They are expected to contribute essentially to study of various astrophysical objects such as AGN, SNe, Gamma-ray bursts (GRBs), X-ray flashes (XRFs), galactic binary sources, stars, CVs, X-ray novae, various transient sources, etc.

The population of HMXBs in the MCs and the Galaxy is investigated. The SMC has an over-abundant population of HMXBs. This provides the clues that the SMC should be more active in massive star formation. The pulse periods in the SMC are slightly shorter than those in the Galaxy, implying that most of the pulsars in Be/X-ray binaries are not spin-up.

We consider the feasibility of detecting neutron star companions to High Mass X-ray Binaries (HMXBs) using astrometric techniques, specifically for accuracies expected for the upcoming Gaia satellite. The direct determination of orbital parameters of HMXBs will increase the census of measured neutron star masses.

A substantial number of stars was detected in the ROSAT All Sky Survey. Analysis of these data indicates a systematic shift in the distribution of their X-ray hardness ratios, from late type dwarfs to late type giants to early type stars, that can be attributed to systematic differences in line-of-sight absorption.

The recurrence time $T_{\rm C}$ of outbursts of the remarkable and unique system, the Rapid Burster (MXB 1730–335), observed by ASM/RXTE, is analyzed by the method of the O–C residuals. The variations of $T_{\rm C}$ are large and occur all the time, but generally they are not chaotic; the mean value of $T_{\rm C}$ is 160 days between the years 1996–2005 but a large shortening of $T_{\rm C}$, accompanied by a large decrease of the maximum intensity $I_{\rm max}$ and the relative energy RE (energy output) of most outbursts, occurred in this interval. The outbursts are found to display a correlation between RE and $I_{\rm max}$, but no correlation with the outburst duration. The observed behaviour is discussed in terms of the thermal instability of the accretion disk. A comparison of this prototype with other neutron star soft X-ray transients, like Aql X-1 and 4U 1608–52, helps us find the common links in the disk behaviour in such systems.

HD34921 has been identified as the counterpart of the X-ray source 4U0515+38 (=1H0521+373). The InfraRed properties are reminiscent of the B[e] system CI Cam. Optical short-term variability suggests a compact companion. We discuss how this system fits in the overall framework of Be stars and X-ray binaries.

The low-frequency (LF) timing noise contaminates residuals of time-of-arrivals (TOAs) of pulsar signals on long time intervals and in some cases can be explained by external astronomical factors not intrinsically related to the pulsar itself. A number of millisecond pulsars located in globular clusters show the LF noise presence in their rotational phase. We discuss a possible origin of this noise as caused by random time variations in the Shapiro time delay caused by flybys of stars of the globular cluster passing near the pulsar line of sight. The Shapiro time delay is integrated over space of parameters characterizing statistical ensemble of stars in the globular cluster and its long-term indeterministic time variation is obtained. We use this result for numerical simulations of the autocovariance function of the LF timing noise and show it can be used for the measuring of the density profile distribution in the globular cluster.

Cataclysmic variables (CVs) formed through close encounters may be the most abundant class of compact binaries in globular clusters. As part of a systematic search for CVs undergoing dwarf nova eruptions (DN) in globular clusters, our 2004 monitoring program of M22 detected an outburst of a CV candidate during May. We present a light curve for the May 2004 period, obtained using the ISIS image subtraction routine. Our ground based results are in good agreement with previous HST measurements, and confirm the DN nature of the outburst and the object's CV status. Further application of the ISIS software will enable us to identify other DN candidates in the core of M22 with the aim of characterizing the properties of these systems, as opposed to similar ones in the field.

We present a new analysis of the light curve of the secondary star in the PSR B1957+20 system. Combining previous data and new data points at minimum from the Hubble Space Telescope, we have 100% coverage in the R-band. We also have a number of new K$_s$ band data points, which we use to constrain the IR magnitude of the system. We model this with the Eclipsing Light Curve code. From the modeling we obtain colour information about the secondary at minimum in BVRI & K. For our best fit model we are able to constrain the system inclination to 66.6 $\pm$ 2.1$^o$ for pulsar masses ranging from 1.35 – 1.9 M$_{\odot}$. The pulsar mass is unconstrained. We also find that the secondary is not filling its Roche lobe, which has important consequences for evolutionary models of this system. The temperature of the un-irradiated side of the companion is in agreement with previous estimates.

We present time-resolved spectroscopy from the January 2005 outburst of the X-ray nova XTE J1118+480. X-ray observations show this outburst to be about half as bright as the previous outburst in 2000. This suggests that the accretion rate was lower than that in the 2000 outburst. Our spectroscopic analysis shows that the emission from the H$\alpha$ line occurs at a higher velocity in the recent outburst compared with the 2000 outburst, more consistent with quiescence/near-quiescence values. This is surprising, considering the $\sim$5 magnitude brightening of the accretion disk relative to its quiescent state.

The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to fine imaging and spectroscopy in the energy range 15 keV to 10 Mev with concurrent X-ray (3-35 keV) and optical monitoring. It was launched on October 17, 2002 and has been succesfully operating ever since. Its two main instruments the spectrometer SPI – optimized for high resolution spectroscopy – and the imager IBIS – optimized for for high resolution imaging – are complemented by the X-ray monitor JEM-X and the optical monitor OMC. All the high energy instruments use coded mask techniques, allowing imaging in the gamma-ray range and combining wide fields of view with high spatial resolution. The presentation gives an overview of the unique properties of INTEGRAL.