We combined deep Chandra, ROSAT HRI, and XMM-Newton observations of M87 to study the impact of AGN outbursts on its gaseous atmosphere. Many X-ray features appear to be a direct result of repetitive AGN outbursts. In particular, the X-ray cavities around the jet and counter jet are likely due to the expansion of radio plasma, while rings of enhanced emission at 14 and 17 kpc are probably shock fronts associated with outbursts that began 1 − 2 × 10 7 years ago. The effects of these shocks are also seen in brightenings within the prominent X-ray arms. On larger scales, ∼50 kpc from the nucleus, depressions in the surface brightness may be remnants of earlier outbursts. As suggested for the Perseus cluster (Fabian et al.), our analysis of the energetics of the M87 outbursts argues that shocks may be the most significant channel for AGN energy input into the cooling flow atmospheres of galaxies, groups, and clusters. For M87, the mean power driving the shock outburst, 2.4 × 10 43 ergs s −1 , is three times greater than the radiative losses from the entire "cooling flow". Thus, even in the absence of other energy inputs, outbursts every 3 × 10 7 years are sufficient to quench the flow.

X‐ray surface brightness fluctuations in the core (650 × 650 kpc) region of the Coma cluster observed with XMM–Newton and Chandra are analysed using a 2D power spectrum approach. The resulting 2D spectra are converted to 3D power spectra of gas density fluctuations. Our independent analyses of the XMM–Newton and Chandra observations are in excellent agreement and provide the most sensitive measurements of surface brightness and density fluctuations for a hot cluster. We find that the characteristic amplitude of the volume filling density fluctuations relative to the smooth underlying density distribution varies from 7–
10 per cent on scales of ∼500 kpc down to ∼5 per cent on scales of ∼30 kpc. On smaller spatial scales, projection effects smear the density fluctuations by a large factor, precluding strong limits on the fluctuations in 3D. On the largest scales probed (hundreds of kpc), the dominant contributions to the observed fluctuations most likely arise from perturbations of the gravitational potential by the two most massive galaxies in Coma, NGC4874 and NGC4889, and the low‐entropy gas brought to the cluster by an infalling group. Other plausible sources of X‐ray surface brightness fluctuations are discussed, including turbulence, metal abundance variations and unresolved sources. Despite a variety of possible origins for density fluctuations, the gas in the Coma cluster core is remarkably homogeneous on scales from ∼500 to ∼30 kpc.

We compare the gravitational potential profiles of the elliptical galaxies NGC 4486 (M87) and NGC 1399 (the central galaxy in the Fornax cluster) derived from X‐ray and optical data. This comparison suggests that the combined contribution of cosmic rays, magnetic fields and microturbulence to the pressure is ∼10 per cent of the gas thermal pressure in the cores of NGC 1399 and M87, although the uncertainties in our model assumptions (e.g. spherical symmetry) are sufficiently large that the contribution could be consistent with zero. In the absence of any other form of non‐thermal pressure support, these upper bounds translate into upper limits on the magnetic field of ∼10–20 μG at a distance of 1–2 arcmin from the centers of NGC 1399 and M87. We show that these results are consistent with the current paradigm of cool cluster cores, based on the assumption that active galactic nuclei regulate the thermal state of the gas by injecting energy into the intracluster medium. The limit of ∼10–20 per cent on the energy density in the form of relativistic protons applies not only to the current state of the gas, but also essentially to the entire history of the intracluster medium, provided that cosmic ray protons evolve adiabatically and that their spatial diffusion is suppressed.

The electron–positron annihilation spectrum observed by SPI/INTEGRAL during deep Galactic Centre region exposure is reported. The line energy (510.954±0.075 keV) is consistent with the unshifted annihilation line. The width of the annihilation line is 2.37 ± 0.25 keV (full width at half‐maximum), while the strength of the ortho‐positronium continuum suggests that the dominant fraction of positrons (94 ± 6 per cent) form positronium before annihilation. Compared to the previous missions, these deep INTEGRAL observations provide the most stringent constraints on the line energy and width. Under the assumption of an annihilation in a single‐phase medium, these spectral parameters can be explained by a warm Te∼ 7000 to 4 × 104 K gas with degree of ionization larger than a few 10−2. One of the widespread phases of the interstellar medium (ISM) – warm (Te∼ 8000 K) and weakly ionized (degree of ionization ∼0.1) – satisfies these criteria. Other single‐phase solutions are also formally allowed by the data (e.g. cold, but substantially ionized ISM), but such solutions are believed to be astrophysically unimportant. The observed spectrum can also be explained by annihilation in a multiphase ISM. The fraction of positrons annihilating in a very hot (Te≥ 106 K) phase is constrained to be less than ∼8 per cent. Neither a moderately hot (Te≥ 105 K) ionized medium nor a very cold (Te≤ 103 K) neutral medium can make a dominant contribution to the observed annihilation spectrum. However, a combination of cold/neutral, warm/neutral and warm/ionized phases in comparable proportions could also be consistent with the data.

The line broadening gives a characteristic mass-weighted ejecta expansion velocity of 10,000 ± 3000 km/s. The observed γ-ray properties are in broad agreement with the canonical model of an explosion of a white dwarf just massive enough to be unstable to gravitational collapse, but do not immediately exclude more complicated merger scenarios, which fuse comparable amount of 56 Ni.The detailed physics of the explosion of type Ia supernovae (for example deflagration or detonation) and the evolution 4,5 of a compact object towards explosion remain a matter of debate [6][7][8][9] . In a majority of models, the ejecta are opaque to γ-ray lines during first 10-20 days after the explosion (because of Compton scattering). At later times, the ejecta become progressively more transparent and a large fraction of γ-rays escapes. This leads to a robust prediction 10 of γ-ray emission from type Ia supernovae after few tens of days, dominated by the γ-ray lines of 56 Co. Such emission has been observed before: the down-scattered hard X-ray continuum from 3The model spectrum is binned similarly to the observed supernova spectrum.The signatures of the 847 and 1,238 keV lines are clearly seen in the spectrum (along with tracers of weaker lines of 56 Co at 511 and 1,038 keV). The low-energy (<400 keV) part of the SPI spectrum is not shown because of possible contamination due to off-diagonal response of the instrument to higher-energy lines. At these energies, we use ISGRI/IBIS data instead (Methods).By varying the assumed position of the source and repeating the flux-fitting procedure using SPI data (Methods) we construct a 40° × 40° image of the signal-tonoise ratio in the 800-880 and 1,200-1,300 keV energy bands (Fig. 2). SN 2014J is detected at 3.9 s.d. and 4.3 s.d. in these two bands, respectively. These are the highest peaks in both images. The emergent lines are expected to be broadened and blueshifted because of ejecta expansion and the opacity effects (Methods and Extended Data Fig. 3). Both effects are indeed observed (Fig. 4). The mean blueshift, averaged over both lines, corresponds to a velocity of V Shift = −3,100 ± 1,100 km s In this model the mass-weighted root-mean-squared velocity of the ejecta is ≈ 12V e = 10, 000 ± 3, 000 km s In more realistic models, based on calculations of explosive nucleosynthesis, the parameters are not independent and the distribution of elements over the ejecta can vary strongly. We therefore compared the expected spectra for several Overall, the good agreement with the canonical models shows that in γ-rays SN 2014J looks like a prototypical type Ia supernova, even though strong and complicated extinction in the optical band makes the overall analysis challenging.

The impact of stochastic gas motions on the metal distribution in cluster core is evaluated. Peaked abundance profiles are a characteristic feature of clusters with cool cores and abundance peaks are likely associated with the brightest cluster galaxies (BCGs) which dwell in cluster cores. The width of the abundance peaks is however significantly broader than the BCG light distribution, suggesting that some gas motions are transporting metals originating from within the BCG. Assuming that this process can be treated as diffusive and using the brightest X-ray cluster A426 (Perseus) as an example, we estimate that a diffusion coefficient of the order of $2 10^{29} {\rm cm^2 s^{-1}}$ is needed to explain the width of the observed abundance profiles. Much lower (higher) diffusion coefficients would result in too peaked (too shallow) profiles. Such diffusion could be produced by stochastic gas motions and our analysis provides constraints on the product of their characteristic velocity and their spatial coherence scale. We speculate that the activity of the supermassive black hole of the BCG is driving the stochastic gas motions in cluster cores. When combined with the assumption that the dissipation of the same motions is a key gas heating mechanism, one can estimate both the velocity and the spatial scale of such a diffusive processes.Comment: 9 pages, 9 figures, submitted to MNRAS typos corrected, references update

Using Chandra observations, we study the X-ray emission of the stellar population in the compact dwarf elliptical galaxy M 32. The proximity of M 32 allows one to resolve all bright point sources with luminosities higher than 8 × 10 33 erg s −1 in the 0.5-7 keV band. The remaining (unresolved) emission closely follows the galaxy's optical light and is characterized by an emissivity per unit stellar mass of ∼4.3 × 10 27 erg s −1 M −1 in the 2-10 keV energy band. The spectrum of the unresolved emission above a few keV smoothly joins the X-ray spectrum of the Milky Way's ridge measured with RXTE and INTEGRAL. These results strongly suggest that weak discrete X-ray sources (accreting white dwarfs and active binary stars) provide the bulk of the "diffuse" emission of this gas-poor galaxy. Within the uncertainties, the average X-ray properties of the M 32 stars are consistent with those of the old stellar population in the Milky Way. The inferred cumulative soft X-ray (0.5-2 keV) emissivity is however smaller than is measured in the immediate Solar vicinity in our Galaxy. This difference is probably linked to the contribution of young (age 1 Gyr) stars, which are abundant in the Solar neighborhood but practically absent in M 32. Combining Chandra, RXTE and INTEGRAL data, we obtain a broad-band (0.5-60 keV) X-ray spectrum of the old stellar population in galaxies.

Aims. We study the spectrum of the cosmic X-ray background (CXB) in energy range ∼5−100 keV. Methods. Early in 2006 the INTEGRAL observatory performed a series of four 30 ks observations with the Earth disk crossing the field of view of the instruments. The modulation of the aperture flux due to occultation of extragalactic objects by the Earth disk was used to obtain the spectrum of the Cosmic X-ray Background (CXB). Various sources of contamination were evaluated, including compact sources, Galactic Ridge emission, CXB reflection by the Earth atmosphere, cosmic ray induced emission by the Earth atmosphere and the Earth auroral emission. Results. The spectrum of the cosmic X-ray background in the energy band 5−100 keV is obtained. The shape of the spectrum is consistent with that obtained previously by the HEAO-1 observatory, while the normalization is ∼10% higher. This difference in normalization can (at least partly) be traced to the different assumptions on the absolute flux from the Crab Nebulae. The increase relative to the earlier adopted value of the absolute flux of the CXB near the energy of maximum luminosity (20−50 keV) has direct implications for the energy release of supermassive black holes in the Universe and their growth at the epoch of the CXB origin.