showing 9 related works from this author
A relativistically smeared spectrum in the neutron star X-ray binary 4U 1705−44: looking at the inner accretion disc with X-ray spectroscopy
2009
Iron emission lines at 6.4-6.97 keV, identified with fluorescent Kalpha transitions, are among the strongest discrete features in the X-ray band. These are therefore one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper we present a recent XMM observation of the X-ray burster 4U 1705-44, where we clearly detect a relativistically smeared iron line at about 6.7 keV, testifying with high statistical significance that the line profile is distorted by high velocity motion in the accretion disc. As expected from disc reflection models, we also find a significant absorption edge at about 8.3 keV; th…
A relativistically smeared line profile in the spectrum of the bright Z-source GX 340+0
2009
We present preliminary results of a 50 ks long XMM-Newton observation of the bright Z-source GX 340+0. We study the temporal and spectral variability of the source, performing a time resolved analysis. In the energy spectra, a broad asymmetric emission line in the Fe Ka energy band is always present. Its shape is compatible with a relativistically smeared profile arising from reflection on a hot accretion disk extending close to the central accreting neutron star. Despite a significant change in the continuum emission and luminosity, the line profile remains substantially unchanged. The line is produced by recombination of highly ionized iron (Fe XXV), the reflecting disk has an inner radiu…
A self-consistent approach to the hard and soft states of 4U 1705-44
2010
We analyzed two XMM-Newton observations of the bright atoll source 4U 1705-44, which can be considered a prototype of the class of the persistent NS LMXBs showing both hard and soft states. The first observation was performed when the source was in a hard low flux state, the second during a soft, high-flux state. Both the spectra show broad iron emission lines. We fit the spectra using a two-component model, together with a reflection model specifically suited to the case of a neutron star, where the incident spectrum has a blackbody shape. In the soft state, the reflection model, convolved with a relativistic smearing component, consistently describes the broad features present in the spec…
DISK REFLECTION SIGNATURES IN THE SPECTRUM OF THE BRIGHT Z-SOURCE GX 340+0
2008
We present the preliminary results of a 50 ks long XMM-Newton observation of the bright Z-source GX 340+0. In this Letter we focus on the study of a broad asymmetric emission line in the Fe K alpha energy band, whose shape is clearly resolved and compatible with a relativistically smeared profile arising from reflection on a hot accretion disk extending close to the central accreting neutron star. By combining temporal and spectral analysis, we are able to follow the evolution of the source along its Horizontal Branch. However, despite a significant change in the continuum emission and luminosity, the line profile does not show any strong correlated variation. This broad line is produced by…
Testing warm Comptonization models for the origin of the soft X-ray excess in AGNs
2018
The X-ray spectra of many active galactic nuclei (AGN) show a soft X-ray excess below 1-2 keV on top of the extrapolated high- energy power law. The origin of this component is uncertain. It could be a signature of relativistically blurred, ionized reflection, or the high-energy tail of thermal Comptonization in a warm (kT $\sim$ 1 keV), optically thick ($\tau\simeq$ 10-20) corona producing the optical/UV to soft X-ray emission. The purpose of the present paper is to test the warm corona model on a statistically significant sample of unabsorbed, radio-quiet AGN with XMM-newton archival data, providing simultaneous optical/UV and X-ray coverage. The sample has 22 objects and 100 observations…
The Large Observatory For x-ray Timing
2014
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final down-selection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supra-nuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m 2 effective area, 2-30 keV, 240 eV spectral resolution, 1 deg collimated field of view) and a WideFi…
The FIGARO II experiment: a general outline of the mission and the principal scientific results
1992
The FIGARO II (French Italian Gamma-Ray Observatory) experiment has been launched successfully three times: in July 1986 from Milo (Trapani), in November 1988 from Charleville (Australia) and in July 1990 again from Milo. In the first flight the observational program was limited to the Crab pulsar PSR0531+21 only because of a telemetry failure: the high sensitivity of FIGARO II allowed an accurate study of the pulse shape as well as a phase-resolved spectroscopy. It was also possible to evaluate the dispersion measure of the Crab pulsar at the flight date from the time delay between gamma-ray and radio pulses. The major results of the second flight were a stringent upper limit to the low-en…
FIGARO IV: Large-area balloon-borne telescope to study rapid time variabilities in the gamma-ray sources at energies above 50 MeV
1993
We present a new γ-ray telescope based on the Limited Streamer Tube technology, used as tracking chambers to detect photons above 100 MeV. This technique allows to obtain very large sensitive areas (16 m2 in our experiment), together with a good angular resolution for payloads embarcable in high-altitude balloon flights. The capability to collect a large signal in a short exposure time makes the telescope particularly suitable and competitive with respect to satellite-based detectors for studying both periodic and random time variabilities on galactic and extragalactic γ-ray sources.
Accretion in strong field gravity with eXTP
2019
In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced 'spectral-timing-polarimetry' techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.