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 whole set of INTEGRAL observations of Type Ia supernova SN 2014J, covering the period 19-162 days after the explosion, has been analyzed. For spectral fitting the data are split into early and late periods covering days 19-35 and 50-162, respectively, optimized for 56 Ni and 56 Co lines. As expected for the early period, much of the gamma-ray signal is confined to energies below ∼200 keV, while for the late period it is strongest above 400 keV. In particular, in the late period, 56 Co lines at 847 and 1248 keV are detected at 4.7σ and 4.3σ, respectively. The light curves in several representative energy bands are calculated for the entire period. The resulting spectra and light curves are compared with a subset of models. We confirm our previous finding that the gamma-ray data are broadly consistent with the expectations for canonical one-dimensional models, such as delayed detonation or deflagration models for a near-Chandrasekhar mass white dwarf. Late optical spectra (day 136 after the explosion) show rather symmetric Co and Fe line profiles, suggesting that, unless the viewing angle is special, the distribution of radioactive elements is symmetric in the ejecta.

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Context. The optical light curve of Type Ia supernovae (SNIa) is powered by thermalized gamma-rays produced by the decay of 56 Ni and 56 Co, the main radioactive isotopes synthesized by the thermonuclear explosion of a C/O white dwarf. Aims. Gamma-rays escaping the ejecta can be used as a diagnostic tool for studying the characteristics of the explosion. In particular, it is expected that the analysis of the early gamma emission, near the maximum of the optical light curve, could provide information about the distribution of the radioactive elements in the debris. Methods. The gamma data obtained from SN2014J in M 82 by the instruments on board INTEGRAL were analysed paying special attention to the effect that the detailed spectral response has on the measurements of the intensity of the lines. Results. The 158 keV emission of 56 Ni has been detected in SN2014J at ∼5σ at low energy with both ISGRI and SPI around the maximum of the optical light curve. After correcting the spectral response of the detector, the fluxes in the lines suggest that, in addition to the bulk of radioactive elements buried in the central layers of the debris, there is a plume of 56 Ni, with a significance of ∼3σ, moving at high velocity and receding from the observer. The mass of the plume is in the range of ∼0.03−0.08 M . Conclusions. No SNIa explosion model has ever predicted the mass and geometrical distribution of 56 Ni suggested here. According to its optical properties, SN2014J looks like a normal SNIa, so it is extremely important to discern whether it is also representative in the gamma-ray band.

The aim of the present report is to emphasize the role of the helium problem as the key one for different aspects of cosmological speculations. This is not surprising, because the processes which produce the helium and other elements in primordial matter take place during the first stages of the cosmological expansion of the Universe.The theory gives three critical values of the He4 abundance in pre-stellar matter, depending on assumptions about the behaviour of the Universe near the singularity. The three critical values are:(1) practically no He4 at all;(2) about 25% of He4 by mass;(3) practically entirely He4.Although intermediate values of He4 are in principle possible, the cosmological models permitting such values are highly improbable. It is obvious that the helium abundance is less than 100%, and that even rough estimates of whether the stellar matter consists almost entirely of hydrogen, or if it has a significant part of He4, are of tremendous importance. The much-more-difficult determination of traces of primeval He3, D, Li6, would be of great help in making definite cosmological conclusions.

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We present results of X-ray observations of the Coma cluster with multiple instruments over a broad energy band. Using the data from INTEGRAL, RXTE and ROSAT observatories, we find that the Coma spectrum in the 0.5 − 107 keV energy band can be well approximated by a thermal plasma emission model with a temperature of T = 8.2 keV. INTEGRAL was used to image the cluster emission in the hard energy band. The cluster is only marginally detectable (∼ 1.6 σ) in the 44−107 keV energy band; however, the raw flux in this band is consistent with the previous results from Beppo-SAX and RXTE observatories. We can exclude with high significance that the hard-band flux reported by Beppo-SAX and RXTE could be produced by a single point source. The 20 − 80 keV flux of a possible non-thermal component in the cluster spectrum is (6.0 ± 8.8) × 10 −12 ergs cm −2 s −1 . It is unlikely that the IC scattering of CMB photons is able to produce hard X-ray flux at these levels, unless the magnetic field strength is as low as 0.2 µG. The latter value can be considered as a lower limit on the field strength in Coma. We also present a temperature map of the central part of the cluster, which shows significant variations and in particular, a hot, ∼ 11.5 keV, region in the extension towards the subcluster infalling from the South-West.