Massive stars emit X-rays. Despite modest X-ray luminosities of single hot massive stars, the ongoing large observing campaigns combining X-ray and UV spectroscopy provide a tomographic view of stellar winds. It is now established that X-ray radiation is modulated with stellar rotation and shows the same period as discrete absorption components (DACs) in the UV resonance lines. The latter are associated with corotating interaction regions (CIRs) in stellar winds, therefore the mechanisms responsible for generation of X-rays and CIRs appear to be physically linked. Binary massive stars with accreting compact companions – high-mass X-ray binaries (HMXBs) – are routinely observed by modern X-ray observatories at Mpc distances. Joint observations in X-ray and UV allow to determine realistic properties of these systems. The brightest sources among HMXBs are ultraluminous X-ray sources (ULXs). Their powerful radiation is an important source of stellar feedback. HMXBs are the products of massive binary evolution and are typically found in the vicinity of young massive star clusters. The superstar clusters blow hot superbubbles which fill large areas in star-forming dwarf galaxies. Recent models show that X-ray emission from superbubbles is likely the dominant source of He ii ionization in metal-poor star-forming dwarf galaxies. To conclude, X-ray observations provide an important window for studying massive stars and their feedback near and far.

The dust properties of the line-of-sight materials in neutron star low-mass X-ray binaries (LMXBs) can be probed by X-ray observations and laboratory experiments. We use a Markov chain Monte Carlo (MCMC) method to conduct a spectral analysis of Chandra ACIS-S/HETG archival data of a sample of LMXBs, including GX 5-1 and GX 13+1. Our MCMC-based analysis puts constraints on the Si K-edge dust properties of the outflowing disk winds in this sample. Further X-ray observations of other LMXBs will help us better understand the grain features of dense outflows and accretion flows in neutron star binary systems.

We present the results of two-dimensional, grid-type hydrodynamical simulations, with parsec-scale central resolution, for the evolution of the hot gas in isolated early-type galaxies (ETGs). The simulations include a physically self-consistent treatment of the mechanical (from winds) and radiative AGN feedback, and were run for a large set of realistic galaxy models. AGN feedback proves to be very important to maintain massive ETGs in a time-averaged quasi-steady state, keeping the star formation at a low level, and the central black hole mass on observed scaling relations. A comparison with recent determinations of the X-ray properties of ETGs in the local universe shows that, at later epochs, AGN feedback does not dramatically alter the gas content originating in stellar recycled material. Thus, the present-day X-ray luminosity is not a robust diagnostic of the impact of AGN activity, within a scenario where the hot gas mostly originates from the stellar population.

Gamma-ray bursts (GRBs) are the most powerful explosive events in the Universe. The prompt gamma emission is followed by an X-ray afterglow that is also detected for over nine hundred GRBs by the Swift BAT and XRT detectors. The X-ray afterglow spectrum bears essential information about the burst, and the surrounding interstellar medium (ISM). Since the radiation travels through the line of sight intergalactic medium and the ISM in the Milky Way, the observed emission is influenced by extragalactic and galactic components. The column density of the Galactic foreground ranges several orders of magnitudes, due to both the large scale distribution of ISM and its small scale structures. We examined the effect of local HI column density on the penetrating X-ray emission, as the first step towards a precise modeling of the measured X-ray spectra. We fitted the X-ray spectra using the Xspec software, and checked how the shape of the initially power low spectrum changes with varying input Galactic HI column density. The total absorbing HI column is a sum of the intrinsic and Galactic component. We also investigated the model results for the intrinsic component varying the Galactic foreground. We found that such variations may alter the intrinsic hydrogen column density up to twenty-five percent. We will briefly discuss its consequences.

The history of supermassive black holes’ activity can be partly constrained by monitoring the diffuse X-ray emission possibly created by the echoes of past events propagating through the molecular clouds of their respective environments. In particular, using this method we have demonstrated that our Galaxy’s supermassive black hole, Sgr A⋆, has experienced multiple periods of higher activity in the last centuries, likely due to several short but very energetic events, and we now investigate the possibility of studying the past activity of other supermassive black holes by applying the same method to M31⋆. We set strong constraints on putative phase transitions of this more distant galactic nucleus but the existence of short events such as the ones observed in the Galactic center cannot be assessed with the upper limits we derived.

Over the past 15 years, the molecular complex Sgr C has been repeatedly observed with both XMM-Newton and Chandra. These observations reveal new features indicating that the region might be more complex than previously thought. We find that its strong iron line emission at 6.4 keV varies significantly over time, which supports the X-ray reflection scenario.

X-ray surveys of normal galaxies, i.e. those that do not host actively supermassive black holes, have revealed important information on the nature of accreting stellar-mass compact objects (neutron stars and black holes), constraints on populations of possible intermediate-mass black holes (102–5M⊙), and on the reservoir of materials in the hot interstellar medium of the most massive galaxies. Here we summarize briefly the results of Chandra and NuSTAR surveys of several samples of galaxies covered during the 2015 IAU General Assembly. This includes a comprehensive study of six nearby starburst galaxies by the NuSTAR mission, of high-redshift galaxies from the 6 Ms Chandra Deep Field South for which evolutionary trends in X-ray emission over cosmic time have been measured, of collisional ring galaxies which are excellent local environments for studying intermediate-mass black holes and of elliptical galaxies which are ideal for study of the hot gas reservoirs containing the effects of stellar and AGN feedback.

We have aggregated together data available in the literature, or analysed by us, to compute the lightcurves of most young supernovae (SNe) that have been detected in X-rays. Currently the database contains about 60 SNe spanning all the various types, but it is expanding rapidly. We use this library of lightcurves and spectra to explore the diversity of SNe, the characteristics of the environment into which they are expanding, and the implications for their progenitors. X-ray spectra can provide insight into the density structure, composition and metallicity of the surrounding medium, and the ionization level, through the spectra themselves as well as the X-ray absorption. Since core-collapse SNe expand mainly in environments created by the progenitor star mass-loss, this can provide crucial information about the nature of the progenitor star, and its mass-loss parameters in the decades or centuries before its death. In a few cases, via detailed modelling, we can distinguish the composition of the SN ejecta from that of the environment. X-ray observations therefore provide an invaluable probe into the stellar environments of core-collapse SNe, complementing data available at other wavelengths. We provide an overview of the X-ray lightcurves of various SN types, the implications for their environment, and clues to their progenitor stars.

Red Supergiants (RSGs) have for decades been assumed to be the progenitors of Type IIP supernovae (SNe). They are expected to have dense winds with mass-loss rates up to 10−4 M⊙ yr−1. We have created a database of available X-ray lightcurves of SNe. Type IIP SNe are found to have the lowest X-ray luminosities among all classes, which is surprising given the high mass-loss rate winds expected from their red supergiant progenitors, and therefore the high density medium into which Type IIP SNe are expected to expand into. We show that the low X-ray luminosity sets a limit on the mass-loss rate of the progenitor star which can collapse to become a RSG, which is about 10−5 M⊙ yr−1. This in turn can be used to set a limit on the initial mass of a RSG star which can become a Type IIP progenitor, which is about 19 M⊙. This is consistent with the limit obtained via direct optical progenitor identification. Optically identified progenitors of Type IIP SNe are found to be RSGs with masses less than about 17 M⊙ (Smartt (2009)). We discuss the implications of this result for stellar evolution, theorize on the fate of RSG stars with initial mass > 19 M⊙, and discuss what type of SNe they will produce at the end of their lifetime.

The circum-nuclear region in an active galaxy is often complex with presence of high excitation gas, collimated radio outflow, and star formation activities, besides the actively accreting supermassive black hole. The unique spatial resolving power of Chandra X-ray imaging spectroscopy enables more investigations to disentangle the active galactic nuclei and starburst activities. For galaxies in the throes of a violent merging event such as NGC6240, we were able to resolve the high temperature gas surrounding its binary active black holes and discovered a large scale soft X-ray halo.

The bulk of the FeKα emission detected in the central molecular zone (CMZ) is thought to be associated with reflection by the central molecular clouds of enhanced past emission from an external X-ray source, most likely Sgr A*. In order to follow the propagation of the reflected emission through the Galactic center (GC), we analyzed all XMM-Newton observations carried out from 2000 to 2012. Preliminary results indicate that while most of the regions that were bright at 6.4 keV in 2000–2001 have a significantly lower flux in 2012, a few other experienced a flux increase. We report for the first time a significant decrease of the FeKα emission in the Sgr C complex, supporting the reflection origin of the 6.4 keV emission detected in this region.

W49B is a mixed-morphology supernova remnant (SNR) with the presence of enhanced abundances and overionization confirmed by X-ray observation. For the overionization, a strong radiative recombination continuum (RRC) has been detected and confirmed by SUZAKU and XMM-Newton. Here, we investigate these intriguing observational results through a multidimensional hydrodynamic model that takes into account, for the first time, the mixing of ejecta with the circumstellar and interstellar medium, thermal conduction, and non-equilibrium ionization. The model can reproduce the morphology and the overionization pattern of W49B. We found that the overionized plasma originates from the rapid cooling of the hot plasma originally heated by the shock reflected from the dense ring-like cloud. In addition, based on the most updated ATOMDB (v2.0.2), we calculated the spectrum of one cell in the overionized region from the simulation results at present. We got the overionized spectrum that is in agreement with the observational results. Thus, our primary result indicates that the model is consistent with the observations both spatially and spectrally.

The fast shocks that characterize supernova remnants heat circumstellar and ejecta material to extremely high temperatures, resulting in significant X-ray emission. The X-ray spectrum from an SNR carries a wealth of information about the temperature and ionization state of the plasma, the density distribution of the postshock material, and the composition of the ejecta. This, in turn, places strong constraints on the properties of the progenitor star, the explosive nucleosynthesis that produced the remnant, the properties of the environment into which the SNR expands, and the effects of particle acceleration on its dynamical evolution. Here I present results from X-ray studies SNRs in various evolutionary states, and highlight key results inferred from the thermal emission.

The 1968 discovery of the Crab and Vela pulsars in their respective supernova remnants (SNRs) confirmed Baade and Zwicky's 1934 prediction that supernovae form neutron stars. Observations of Pulsar Wind Nebulae (PWNe), particularly with the Chandra X-ray Observatory, have in the past decade opened a new window to focus on the neutron stars' relativistic winds, study their interaction with their hosting SNRs, and find previously missed pulsars. While the Crab has been thought for decades to represent the prototype of PWNe, we now know of different classes of neutron stars and PWNe whose properties differ from the Crab. In this talk, I review the current status of neutron stars/PWNe-SNRs associations, and highlight the growing diversity of PWNe with an X-ray eye on their association with highly magnetized neutron stars. I conclude with an outlook to future high-energy studies.

The distinction between the high-magnetic field pulsars (HBPs, thought to be mainly rotation-powered) and magnetars (commonly believed to be powered by their super-strong magnetic fields) has been recently blurred with the discovery of magnetar-like activity from the HBP J1846–0258 in the SNR Kes 75. What determines the spin properties of a neutron star at birth and its manifestation as a magnetar-like or more classical pulsar is still not clear. Furthermore, although a few studies have suggested very massive progenitors for magnetars, there is currently no consensus on the progenitors of these objects. To address these questions, we examine their environments by studying or revisiting their securely associated SNRs. Our approach is to: 1) infer the mass of their progenitor stars through X-ray spectroscopic studies of the thermally emitting supernova ejecta, and 2) investigate the physical properties of their hosting SNRs and ambient conditions. We here highlight our detailed studies of two SNRs: G292.2–0.5, associated with the HBP J1119–6127, and Kes 73, associated with the AXP 1E 1841–045, and summarize the current view of the other (handful) HBP/magnetar-SNR associations.

We examine the innermost 100 parsec scale region of the Seyfert 2 galaxy NGC 1068 using a high spatial resolution X-ray image obtained with the Chandra X-ray Observatory, which allows comparison between X-ray emission clumps, optical narrow line ([OIII]) clouds and sub-arcsecond scale radio jet. Based on the combined X-ray, [OIII], and radio continuum morphology, we identify the locations of intense radio jet-cloud interaction. The [OIII] to soft X-ray ratios show that some of these clouds are strongly affected by shock heating. We estimate that the kinematic luminosity of the jet-driven shocks is 6 × 1038 erg s−1.

We present XMM-Newton and Chandra observations of the born-again planetary nebula A 30. These X-ray observations reveal a bright unresolved source at the position of the central star whose X-ray luminosity exceeds by far the model expectations for photospheric emission and for shocks within the stellar wind. We suggest that a “born-again hot bubble” may be responsible for this X-ray emission. Diffuse X-ray emission associated with the petal-like features and one of the H-poor knots seen in the optical is also found. The weakened emission of carbon lines in the spectrum of the diffuse emission can be interpreted as the dilution of stellar wind by mass-loading or as the detection of material ejected during a very late thermal pulse.

The photospheric emission from the hottest central stars of planetary nebulae (CSPNe) is capable to extend into the X-ray domain, with emission peaking at 0.1-0.2 keV and vanishing above 0.4 keV. Unexpected, intriguing hard X-ray emission with energies greater than 0.5 keV has been reported for several CSPNe and for a number of white dwarfs (WDs). Different mechanisms may be responsible for the hard X-ray emission from CSPNe and WDs: coronal emission from a late-type companion, shocks in fast winds as in OB stars, leakage from underneath the star photosphere, or accretion of material from a disk, a companion star, or the circumstellar medium. Therefore, the hard X-ray emission associated with CSPNe may have significant implications for our understanding of the formation of PNe: binary companions, disks, and magnetic fields are thought to play a major role in the shaping of PNe, whereas clumping in the stellar wind may have notable effects in the PN evolution by modifying the stellar mechanical energy output. Here I present the results of different observational efforts to search for hard X-ray emission from CSPNe and discuss the different mechanisms for the production of hard X-rays.

X-ray observations reveal extended halos around early-type galaxies which enable us to trace the dark matter distribution around the galaxies (see Mathews and Brighenti 2003 for a review). X-ray luminosities, LX of massive early-type galaxies are 1040−1042 erg s−1 in 0.3–2 keV. The correlation plot between LX and B-band luminosity LB shows a large scatter in the sense that LX varies by 2 orders of magnitudes for the same LB, in the brightest end (log LB ≳ 10.5). The amount of the X-ray hot gas in early-type galaxies is typically a few % of the stellar mass, in contrast to clusters of galaxies which hold ~5 times more massive gas than stars. Matsushita (2001) showed that X-ray luminous galaxies are characterized by extended X-ray halo with a few tens of re, similar to the scale of galaxy groups, so the presence of group-size potentials would be strongly linked with the problem of large LX scatter.

Using Chandra and XMM-Newton X-ray observations of young, post-merger elliptical galaxies, we present X-ray characteristics of age-related observational results, by comparing with typical old elliptical galaxies in terms of X-ray properties of their low-mass X-ray binaries (LMXBs) and hot interstellar matter (ISM).