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 1e8 K optically thin thermal plasma, with a prominent iron emission line at 6.7 keV. 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 gas. To replenish the energy losses requires a source of 10^{43} erg/s, 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 6-7 keV, 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.Comment: 16 pages, 3 figures. Draft version of the paper that will appear in Nature, Issue April 30, 200

New nearby AGNs from all sky surveys of INTEGRAL and RXTE observatories

We present first results of a campaign of optical identifications of X-ray sources discovered by RXTE and INTEGRAL observatories during their sky surveys. In this work we study six newly discovered nearby active galactic nuclei at z<0.1. The optical spectrophotometric data were obtained with Russian-Turkish 1.5-m telescope (RTT150). We present their redshifts and main parameters of brightest emission lines.Comment: 6 pages, Astronomy Letters, in pres

IGR J16318-4848: an X-ray source in a dense envelope?

The hard X-ray source IGR J16318-4848 was recently discovered by the INTEGRAL observatory (Courvoisier et al.) and subsequently uncovered in archival data of ASCA observations in 1994 (Murakami et al.). We present results of a detailed analysis of the ASCA data. The spectrum of the source in the 0.5--10 keV band is extraordinarily hard and is virtually unobservable below 4 keV because of strong photoabsorption NHL L>4e23 cm^-2. The 4--10 keV emission is dominated by a Kalpha line of neutral or weakly ionized iron with an equivalent width of \~2.5 keV. There is also an indication for a second line at ~7 keV. Our analysis of archival observations of the IGR J16318-4848 infrared counterpart, discovered by Foschini et al., shows that the point source is detected at different wavelengths in the 1--15 micron range. The available data suggest that IGR J16318-4848 is an X-ray binary system enshrouded by a dense envelope. It is possible that the source is a wind-fed high-mass X-ray binary similar to GX 301-2. We argue that IGR J16318-4848 might be the first representative of a previously unknown population of highly absorbed galactic X-ray sources, which remained undetected with X-ray missions before INTEGRAL.Comment: Accepted for publication in Astronomy Letter

Detection of blueshifted emission and absorption and a relativistic Iron line in the X-ray spectrum of ESO 323-G077

We report on the X-ray observation of the Seyfert 1 ESO323-G077 performed with XMM-Newton. The spectra show a complex spectrum with conspicuous absorption and emission features. The continuum emission can be modelled with a power law with an index of 1.99+/-0.02 in the whole XMM-Newton energy band, marginally consistent with typical values of Type-I objects. An absorption component with an uncommonly high equivalent Hydrogen column, n_H=5.82(+0.12/-0.11)x10^22 cm-2, is affecting the soft part of the spectrum. Additionally, two warm absorption components are also present. The lower ionised one has an ionisation parameter of Log(U)=2.14(+0.06/-0.07) and an outflowing velocity of v=3200(+600/-200) km/s. Two absorption lines located at ~6.7 and ~7.0 keV can be modelled with the highly ionised absorber. The ionisation parameter and outflowing velocity of the gas measured are Log(U)=3.26(+0.19/-0.15) and v=1700(+600/-400) km/s, respectively. Four emission lines were also detected in the soft energy band. The most likely explanation for these emission lines is that they are associated with an outflowing gas with a velocity of ~2000 km/s. The data suggest that the same gas which is causing the absorption could also being responsible of these emission features. Finally, the spectrum shows the presence of a relativistic iron emission line likely originated in the accretion disc of a Kerr BH with an inclination of ~25 deg. We propose a model to explain the observed X-ray properties which invokes the presence of a two-phase outflow with cone-like structure and a velocity of the order of 2,000-4,000 km/s. The inner layer of the cone would be less ionised, or even neutral, than the outer layer. The inclination angle would be lower than the opening angle of the outflowing cone.Comment: 11 pages, accepted in MNRA

Traces of past activity in the Galactic Centre

The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of ~4*10^6 M_Sun. Sgr A*, its electromagnetic counterpart, currently appears as an extremely weak source with a luminosity L~10^-9 L_Edd. The lowest known Eddington ratio BH. However, it was not always so; traces of "glorious" active periods can be found in the surrounding medium. We review here our current view of the X-ray emission from the Galactic Center (GC) and its environment, and the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the history of Sgr A*'s past activity and its impact on the surrounding medium. The structure of the Central Molecular Zone (CMZ) has not changed significantly since the last active phase of Sgr A*. This relic torus provides us with the opportunity to image the structure of an AGN torus in exquisite detail.Comment: Invited refereed review. Chapter of the book: "Cosmic ray induced phenomenology in star forming environments" (eds. Olaf Reimer and Diego F. Torres

Fitting the Gamma-Ray Spectrum from Dark Matter with DMFIT: GLAST and the Galactic Center Region

We study the potential of GLAST to unveil particle dark matter properties with gamma-ray observations of the Galactic center region. We present full GLAST simulations including all gamma-ray sources known to date in a region of 4 degrees around the Galactic center, in addition to the diffuse gamma-ray background and to the dark matter signal. We introduce DMFIT, a tool that allows one to fit gamma-ray emission from pair-annihilation of generic particle dark matter models and to extract information on the mass, normalization and annihilation branching ratios into Standard Model final states. We assess the impact and systematic effects of background modeling and theoretical priors on the reconstruction of dark matter particle properties. Our detailed simulations demonstrate that for some well motivated supersymmetric dark matter setups with one year of GLAST data it will be possible not only to significantly detect a dark matter signal over background, but also to estimate the dark matter mass and its dominant pair-annihilation mode.Comment: 37 pages, 16 figures, submitted to JCA