S. Sazonov

Discrete sources as the origin of the galactic X-ray ridge emission

An unresolved X-ray glow (at energies above a few kiloelectronvolts) was discovered about 25 years ago and found to be coincident with the Galactic disk—the Galactic ridge X-ray emission. This emission has a spectrum characteristic of a ∼108u2009K optically thin thermal plasma, with a prominent iron emission line at 6.7u2009keV. The gravitational well of the Galactic disk, however, is far too shallow to confine such a hot interstellar medium; instead, it would flow away at a velocity of a few thousand kilometres per second, exceeding the speed of sound in the gas. To replenish the energy losses requires a source of 1043u2009ergu2009s-1, exceeding by orders of magnitude all plausible energy sources in the Milky Way. An alternative is that the hot plasma is bound to a multitude of faint sources, which is supported by the recently observed similarities in the X-ray and near-infrared surface brightness distributions (the latter traces the Galactic stellar distribution). Here we report that at energies of ∼6–7u2009keV, more than 80 per cent of the seemingly diffuse X-ray emission is resolved into discrete sources, probably accreting white dwarfs and coronally active stars.

INTEGRAL/IBIS 7-year All-Sky Hard X-ray Survey - I. Image reconstruction

This paper is the first in a series devoted to the hard X-ray whole sky survey performed by the INTEGRAL observatory over seven years. Here we present an improved method for image reconstruction with the IBIS coded mask telescope. The main improvements are related to the suppression of systematic effects which strongly limit sensitivity in the region of the Galactic Plane (GP), especially in the crowded field of the Galactic Center (GC). We extended the IBIS/ISGRI background model to take into account the Galactic Ridge X-ray Emission (GRXE). To suppress residual systematic artifacts on a reconstructed sky image we applied nonparametric sky image filtering based on wavelet decomposition. The implemented modifications of the sky reconstruction method decrease the systematic noise in the ~20 Ms deep field of GC by ~44%, and practically remove it from the high-latitude sky images. New observational data sets, along with an improved reconstruction algorithm, allow us to conduct the hard X-ray survey with the best currently available minimal sensitivity 3.7E-12 erg/s/cm2 ~0.26 mCrab in the 17-60 keV band at a 5 sigma detection level. The survey covers 90% of the sky down to the flux limit of 6.2E-11 erg/s/cm2 (~4.32 mCrab) and 10% of the sky area down to the flux limit of 8.6E-12 erg/s/cm2 (~0.60 mCrab).

Identification of 8 INTEGRAL hard X-ray sources with Chandra

We report the results of identification of 8 hard X-ray sources discovered by the INTEGRAL observatory during the ongoing all-sky survey. These sources have been observed by Chandra. In 6xa0cases a bright X-ray source was found within the INTEGRAL localization region, which permitted to unambiguously identify 5 of the objects with nearby galaxies, implying that they have an active galactic nucleus (AGN), whereas one source is likely an X-ray binary in LMC. 4 of the 5xa0newly discovered AGNs have measured redshifts in the range 0.025–0.055. The X-ray spectra reveal the presence of significant amounts of absorbing gas (

Positron annihilation spectrum from the Galactic Centre region observed by SPI/INTEGRAL revisited: annihilation in a cooling ISM?

N_mathrm{H}

GRANAT/WATCH catalogue of cosmic gamma-ray bursts: December 1989 to September 1994

in the range 10 22 –10 24 xa0cm -2 ) in all 5xa0AGNs, demonstrating that INTEGRAL is starting to fill in the sample of nearby obscured AGNs.

Luminosity function of faint Galactic sources in the Chandra bulge field

We analyse SPI/INTEGRAL data on the 511 keV line from the Galactic Centre, accumulated over ∼6 years of observations. We decompose the X-ray and soft gammaray emission of the central part of the Milky Way into a relatively compact “Bulge” and a more extended “Disk” components and report their spectral properties. The Bulge component shows a prominent 511 keV line and essentially no flux at 1.8 MeV, while the Disk component on the contrary contains a prominent 1.8 MeV line and a very weak annihilation line. We show that the spectral shape of the annihilation radiation (the narrow 511 keV line and the associated othro-positronium continuum) is surprisingly well described by a model of annihilation of hot positrons in a radiatively cooling interstellar medium (ISM). The model assumes that positrons are initially injected into a hot (∼ 10 K), volume filling ISM, which is allowed to freely cool via radiative losses. The annihilation time in such a medium is longer than the cooling time for temperatures higher than a few 10 K. Thus, most of the positrons annihilate only after the gas has cooled down to ∼ 10 K, giving rise to annihilation emission characteristic of a warm, ionized ISM.

Scattering in the inner accretion disk and the waveforms and polarization of millisecond flux oscillations in LMXBs

We present the catalogue of gamma-ray bursts (GRB) observed with the WATCH all-sky monitor on board the GRANAT satellite during the period December 1989 to September 1994. The cosmic origin of 95 bursts comprising the catalogue is confirmed either by their localization with WATCH or by their detection with other GRB experiments. For each burst its time history and information on its intensity in the two energy ranges

Impact of thermal diffusion and other abundance anomalies on cosmological uses of galaxy clusters

8{-}20

SRG/eROSITA prospects for the detection of GRB afterglows

xa0keV and

INTEGRAL constraints on the galactic hard X-ray background from the Milky Way anticenter

20{-}60