ISDC Science Results

Mildly obscured active galaxies and the cosmic X-ray background
2016-08-18 | INTEGRAL, HEAVENS, AGN, Diffuse emission
We have produced the deepest hard X-ray images of Active Galactic Nuclei, which show that midly obscured sources have a stronger reflection than unobscured objects. Mildly obscured Active Galactic Nuclei contribute massively to the cosmic X-ray background such that a population of Compton thick sources larger than that effectively detected is not required. The stronger reflection suggests that the covering fraction of the gas and dust surrounding their central engines is a key factor shaping their appearance.

The high energy spectrum of 3C 273
2015-03-12 | AGN, INTEGRAL, Fermi
We studied the high energy spectral variability of the bright quasar 3C 273 from ~1 keV up to ~10 GeV using data collected with RXTE-PCA, INTEGRAL and Fermi/LAT and compared them with radio data at 37 GHz collected at the Metsähovi Radio Observatory. Quasi-simultaneous broad band high energy spectra have been built at the epoch of γ ray flares and X-ray flares. Both timing and spectral analysis suggest a two-component scenario, where the X-ray emission is likely dominated by a Seyfert-like component, while the γ ray emission is dominated by a blazar-like component originated in the relativistic jet.

The environment of Weak Emission-Line Quasars
2011-11-17 | AGN
We analyse the ultraviolet and X-ray properties of 83 weak emission-line quasars (WLQ) and ~240 ordinary quasars to answer whether the Baldwin effect is responsible for the unusual weakness of emission-lines in WLQ or not. We find that this weakness is rather caused by a low covering factor of the broad line region in WLQ than by their extremely soft ionizing continuum.

Multiple synchrotron self-Compton modeling of gamma-ray flares in 3C 279
2011-09-27 | AGN
We test and constrain a new theoretical model for the high-energy emission of blazars. We fit the model parameters to longterm lightcurves and to radio-to-gamma-ray spectra of 3C 279. It turns out that the modeling of shock waves in a jet emitting synchrotron self-Compton radiation including multiple-order scatterings is a promising alternative to the usual external-Compton emission models.

Reflection in Seyfert galaxies and the unified model of AGN
2011-08-02 | INTEGRAL, AGN, Diffuse emission | Press Release
From an extremely long hard X-ray look at AGN we found unexpected differences amongst different classes of objects. These differences could be explained by supermassive black holes living in different environments, and might help shading light on the origin of the peak of the cosmic X-ray background.

Stochastic Acceleration and the Evolution of Spectral Distributions in SSC Sources: A Self Consistent Modeling of Blazars' Flares
2011-07-12 | AGN, VHE
We investigated the role of the stochastic acceleration on the evolution of the particle energy distribution in relativistic jet, taking into account radiative losses in a SSC scenario. We find that in the acceleration dominated stage the distribution is well described by a log-parabolic shape, and that the predicted trends among synchrotron curvature (b_s), peak energy (E_s), and peak luminosities (L_s), match those observed in a sample of 6 TeV detected BL Lacs.

Seyfert 2 galaxies in the GeV band: jets and starburst
2010-10-18 | Fermi, AGN, INTEGRAL
We present Fermi/LAT data analysis of two unusual suspects in the GeV band, NGC 1068 and NGC 4945, which are both composite starburst/active galactic nuclei objects. We show that the GeV emission of NGC 4945 could be interpreted in terms of starburst activity, while the one of NGC 1068 should account for a dominant contribution from the central AGN.

Shock-in-jet model for quasars and microquasars
2010-10-06 | AGN, X-ray binary
We present the detailed equations for a physical modeling of the synchrotron emission of shock waves propagating in a relativistic jet. We illustrate this by fitting a series of model outbursts to a flaring episode observed in the radio and infrared emission of the microquasar Cyg X-3 and derive the physical conditions in the jet flow.

Multi-zone warm and cold clumpy absorbers in 3 Seyfert galaxies
2010-05-10 | AGN, INTEGRAL
We performed the spectral analysis of 3 Seyfert galaxies presenting evidence of a strong soft excess below 2 keV. We showed how this soft excess can be related only to a clumpy structure of the absorbers, and does not need any additional emission component.

Evidence for strong extragalactic magnetic fields from Fermi observations of TeV blazars
2010-04-04 | Fermi, AGN, VHE | Press Release
FERMI/LAT observations of distant blazars together with theoretical modeling provide us with the first clue about the parameters of primordial magnetic field, survived up to nowadays in the voids of the Large-Scale Structure.

X-ray power law spectra in active galactic nuclei
2010-01-23 | AGN
We discuss X-ray spectral properties in AGN within the framework of clumpy accretion flows in which shocks between accreting elements account for the observed radiation. We obtain that steeper spectra are associated with shorter characteristic timescales, in agreement with the recently discovered "spectral-timing" correlation.

INTEGRAL spectra of the cosmic X-ray background and Galactic ridge emission
2010-01-14 | INTEGRAL, Diffuse emission, AGN, X-ray binary
We reanalyzed the INTEGRAL Earth occultation observations of early 2006 to derive IBIS spectra of the cosmic X-ray background (CXB) and of the Galactic ridge X-ray emission (GRXE) in the ~20-200 keV range. The potential of such observations is demonstrated by the state-of-the-art hard X-ray spectra we derived for three fundamental components: the CXB, the GRXE and the Earth emission.