Related papers: X-ray variability and correlations in the two phas…
We present the UV/X-ray joint spectral analyses of four Seyfert~1 galaxies (PG 0804+761, NGC 7469, SWIFT J1921.1-5842, and SWIFT J1835.0+3240) using the data acquired with the Ultraviolet Imaging Telescope and Soft X-ray Telescope onboard…
We fitted the $3-180$-keV spectrum of all the observations of the neutron-star low-mass X-ray binary 4U 1636$-$53 taken with the {\it Rossi X-ray Timing Explorer} using a model that includes a thermal Comptonisation component. We found that…
The Chandra X-ray observatory monitored the single cool star, AB Doradus, continuously for a period lasting 88 ksec (1.98 Prot) in 2002 December with the LETG/HRC-S. The X-ray lightcurve shows rotational modulation, with three peaks that…
We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGN) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband ($0.3\mbox{--}79$ keV) spectrum shows the presence of a…
Observationally, it is found that there is a strong correlation between the hard X-ray photon index $\Gamma$ and the Compton reflection scaling factor $\Re$ in active galactic nuclei. In this paper, we propose that the $\Gamma-\Re$…
We present preliminary results of the spectral analysis of a large sample of Seyfert galaxies observed by BeppoSAX. The only selection criterium was a sufficiently large S/N ratio (>10) in the PDS band (12-200 keV) to allow good detection…
We execute a detailed spectral-timing study of Cygnus X-1 in the low/hard, intermediate and high/soft states with the Hard X-ray Modulation Telescope observations. The broad band energy spectra fit well with the "truncated disk model" with…
Existence of relatively cool ($k_B T \lesssim 10~{\rm keV}$) and optically thick ($\tau \gtrsim 3$) coronae are inferred above super-Eddington accretion flow such as ultraluminous X-ray sources (ULXs), GRS 1915+105, and narrow-line Seyfert…
A long-standing question in active galactic nucleus (AGN) research is how the corona is heated up to produce X-ray radiation much stronger than that arising from the viscous heating within the corona. In this paper, we carry out detailed…
We review observations and theoretical models of X-ray/gamma-ray spectra of radio-quiet Seyfert galaxies and of Galactic black-hole candidates (in the hard spectral state). The observed spectra share all their basic components: an…
(truncated version) The X-ray spectra of Galactic binary systems in the very high state show both strong disk emission and a strong, steep tail to high energies. We use simultaneous optical-ASCA-RXTE data from the black hole transient XTE…
We discuss recent results on the Seyfert spectral variability. Their observed high energy variability is generally consistent with X-ray spectral slop fluctuations produced by change of the soft photon luminosity in the sense that spectra…
We use a model-independent technique to investigate the nature of the 2-15 keV X-ray spectral variability in four Seyfert galaxies and distinguish between spectral pivoting and the two-component model for spectral variability. Our analysis…
We present a spectral analysis of two XMM-Newton observations of the narrow-line Seyfert 1 galaxy UGC 11763. UGC 11763 shows very different soft X-ray spectral shapes in the two observations separated by 12 years. Three spectral models are…
Seyfert galaxies have been shown to exhibit a large variety of features in their X-ray spectra from which the environment of the central engine can be deduced. We focus on the two following aspects: the Warm Absorber, mainly responsible of…
We use time domain analysis techniques to investigate the rapid variability of Cygnus X-1. We show that the cross-correlation functions between hard and soft energy bands reach values very close to unity and peak at a lag of less than 2…
The corona, a hot cloud of electrons close to the centre of the accretion disc, produces the hard X-ray power-law continuum commonly seen in luminous Active Galactic Nuclei (AGN). The continuum has a high-energy turnover, typically in the…
(Abridged) Soft and hard X-ray excesses, compared to the continuum power-law shape between ~2-10 keV, are common features observed in the spectra of active galactic nuclei (AGN) and are associated with the accretion disc-corona system…
The spectral shape of the hard X-ray continuum of Active Galactic Nuclei (AGN) can be ascribed to inverse Compton scattering of optical/UV seed photons from the accretion disc by a hot corona of electrons. This physical process produces a…
Thermal conduction between a cool accretion disk and a hot inner corona can result in either evaporation of the disk or condensation of the hot corona. At low mass accretion rates, evaporation dominates and can completely remove the inner…