The heart of the Milky Way is a laboratory for high energy astrophysics, containing the Galactic supermassive black hole, thousands of X-ray point sources and prominent diffuse X-ray emission. I will review our knowledge of the present and past activity from the supermassive black hole as well as its relation to the recently discovered outflow connecting the central parsecs to the base of the...
Variable X-ray emission from the clouds of the Central Molecular Zone (CMZ) are attributed to the reflection of radiation emitted by the super-massive Black Hole of the Galaxy, Sgr A$^*$, during outbursts occurred in the recent (< 1000 yr) past.
Thanks to a detailed analysis of the XMM and Chandra data of the Galactic Center, based on the comparison of observed spectra and Monte Carlo...
I will review recent (and not so recent) results on accretion and ejection processes in X-ray binaries.
Characterization of X-ray binaries on the basis of their donor stars allow us to identify their parent stellar populations and measure directly their formation efficiency as function of their age. Combining this information with constraints on the nature of their compact objects allow us to measure the formation rate of compact objects and their demographics in different types of X-ray...
The sub-class of high mass X-ray binaries called Supergiant Fast X-ray Transients (SFXTs) shows flaring activity even outside outbursts, across more than four orders of magnitude in X-ray luminosity. We investigated these X-ray flares exploiting the XMM-Newton archival observations, taking advantage of the EPIC (0.2-12 keV) products made publicly available by the EXTraS project. Adopting the...
We report the detection of pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new observations of this object, with a period of $\sim 1.5$ s and a pulsed fraction of $\sim 5\%$. We demonstrate that the moderate significances of the individual detections are unlikely to originate in...
Ultraluminous X-ray sources (ULXs) are extragalactic X-ray emitters located off-center of their host galaxy and with a luminosity in excess of a few $10^{39}$ erg/s, if emitted isotropically. The discovery of periodic modulation revealed that in some ULXs the accreting compact object is a neutron star (NS), indicating luminosities substantially above their Eddington limit. The most extreme...
Observational studies of Ultraluminous X-ray Sources (ULXs, L > 1e39 erg/s) have taken on greater siginficance since the discovery that this population is (primarily) made up of X-ray binaries accreting at super-Eddington rates, a result that has been spectacularly confirmed with the detection of coherent pulsations from a growing number of ULXs (requiring neutron star accretors, despite...
Accretion is known to occur at rates far in excess of the classical Eddington limit in the local and distant Universe alike. In our Galaxy we are provided with a view of such accretion in the form of the extreme binary SS433, observations of which tell us that mass-loaded outflows and persistent collimated jets are associated features which redistribute energy and matter into the local...
Powerful accretion processes around black holes (BH) in X-ray binaries or AGN give birth to High energy emission from UV to X-rays/gamma-rays. While the BHs strongly differ in terms of mass in these objects, their close environment shows clear similarities with the presence of (1) an optically thick accretion disk, (2) a hot plasma (the so-called corona) producing hard X-rays through...
In high mass X-ray binaries (HMXBs), the black hole or neutron star accretes matter from the wind of a massive supergiant companion: the stellar wind drives changes in the accretion and thus the system’s X-ray emission. But the interaction of this emission with the wind material can also be used to study the wind itself, in particular its geometry, porosity (or clumpiness), mass-loss rate and...
Hercules X-1 is one of the best studied accreting neutron star X-ray binaries with a wealth of archival X-ray data. It is well-known for the various time periods in its system: a 35-day period of high, low and short-on flux states, likely caused by a precessing warped accretion disc, a 1.7 day orbital period and a 1.2 sec pulsation period of a neutron star with a ∼10^12 G magnetic field. I...
With the detection of compact-object mergers with LIGO/VIRGO there is a resurgence in modeling efforts to understand the evolution of interacting close binaries, including X-ray binaries (XRBs). Critical high-value empirical constraints on this effort can be gained by XRB X-ray luminosity functions (XLFs), which provide many degrees of freedom for testing models. Using a sample of 38 nearby...
In the local Universe, it is observed that the X-ray luminosity ($L_X$) of HMXB populations is correlated with the host galaxy’s star formation rate (SFR). Recent X-ray studies of high-redshift galaxies find a positive evolution of this correlation with redshift. This trend is attributed to the formation of more luminous HMXBs in lower metallicity ($Z$) environments, as predicted by binary...
Supernovae are one of the most energetic explosion events in the universe, with the human detectability not only in electromagnetic wave but also neutrino and possibly gravitational wave. They also play the main role of chemical evolution of the universe. On the other hand, the explosion mechanism in detail is still unclear. We will summarize recent X-ray observations of remnants of supernovae...
Type IIn supernovae (SNe) are characterized by narrow lines on a broad base in their optical spectrum. A wide diversity in their lightcurves, and in SNe that exhibit IIn features, has greatly complicated the task of identifying their progenitors. IIns have the highest X-ray luminosity of all SN classes, and are observable in X-rays decades after explosion. Many of the lightcurves tend to fall...
Cataclysmic variables (CVs; interacting binaries in which a white dwarf accretes matter from a Roche-lobe filling donor on or near the main sequence) and symbiotic stars (white dwarf-red giant binaries) are excellent laboratories in which to study accretion physics, without having to worry about relativistic effects. Their fluxes are high enough to enable detailed X-ray and multiwavelength...
High-resolution X-ray spectroscopy offers a unique and powerful way to establish the properties of dust grains in the interstellar medium of our Galaxy. Defining the dust chemistry is an excellent tracer of structure formation and evolution in the Galaxy. Diagnostic features in the spectra of X-ray sources, like oxygen, magnesium, silicon and iron K-edges, can be used to determine the chemical...
X-ray observations performed during the last few decades have provided a rich data base on black-hole X-ray binaries. A strong coupling between the properties of the accretion flow and the presence of outflows, such as radio-jets and hot X-ray winds, has been found to be a fundamental characteristic of their powerful outbursts.
Since 2015 we have discovered optical accretion disc winds in...
