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.
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The stellar wind velocity field of HD 77581
2015-07-07 | INTEGRAL, HEAVENS, X-ray binary
The early acceleration of stellar winds in massive stars is poorly constrained. The comparison of X-ray observations of the high-mass X-ray binary Vela X-1 accumulated over 9 years, with hydodynamical simulations allows to constrain the stellar wind velocity field very close to the surface of the super-giant companion. The observed acceletration is more efficient than usually assumed.
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Un-Beamed Tidal Disruption Events at Hard X-Rays
2015-05-27 | HEAVENS
We have detected nine TDE candidates at hard X-rays during eight years in a sample of ~53'000 galaxies closer than 100 Mpc. The observed hard X-ray fluxes and rate are consistent with the rates observed by XMM-Newton at soft X-rays or in the optical from SDSS observations and also consistent with expectations from simulations. The average hard X-ray spectral shape of our TDE candidates is in addition very similar to that usually observed in active galactic nuclei, pointing towards inverse Compton processes and electrons accelerated in shocks in the accretion flow.
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Origin of the X-ray off-states in Vela X-1
2014-12-22 | INTEGRAL, X-ray binary, HEAVENS
INTEGRAL discovered huge hard X-ray variability and off-sates in Vela X-1 and other high mass X-ray binaries. Hydrodynamic simulations allowed us to discover the likely source for such variations occuring on time scales of hours. These variations are related to oscillations of the accretion rate (with a typical period of ∼ 6800 sec) corresponding to the complex motion of a bow shock forming between the neutron star and the massive companion, moving either towards or away from the neutron star.
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