arXiv subjects
Publications and source records attributed to Luigi Foschini.
Let's take stock of the situation on one of the most studied astrophysical phenomena during the latest years: the jets escaping from protostars, stellar singularities, GRB and active galactic nuclei.
With its large collection area, broad-band energy coverage from optical/NIR (0.3 to 2.2 micron) to soft/hard X-ray (0.1-600 keV), all-sky monitoring capability, and on-board follow-up, the proposed Energetic X-ray Imaging Survey Telescope mission (EXIST, see L. Natalucci contribution at this conference) has been designed to properly tackle the study of the AGN phenomenon and the role that SMBH play in the Universe. In particular EXIST will carry out an unprecedented survey above 10 keV (a factor ~20 increase in hard X-ray sensitivity compared to current and prior X-ray missions) of SMBH activity, not just in space but also in time and over a significant expanded energy range; this strategy will overcome previous selection biases, will break the "multi-wavelength" identification bottleneck and will dramatically increase the number of AGN detected above 10 keV that are amenable to detailed follow-up studies (~50000 AGN are expected). We discuss here on few selected AGN science topics enabled by the unique combination of EXIST's instruments. In particular EXIST will enable major progress in understanding: i) when and where SMBH are active in the Universe (by revealing and measuring heavily obscured accretion in the local - z<0.5 - Universe), ii) the physics of how SMBH accrete (by studying the broad-band X-ray spectra and variability properties of an unbiased and significant sample of AGN), and iii) the link between accretion power and jet/outflow power (by using observations of blazars). Last but not least EXIST's ability to find powerful, but very rare blazars, enables it to probe the appearance of the very first SMBH in the Universe allowing us to set strong constraints on the models of SMBH formation and early growth in the Universe.
By using the Fermi satellite, a group of physicists discovers a new type of gamma-ray active nucleus
These notes were originally prepared as additional material for the lessons I have given at the summer school Gamma-ray Astrophysics and Multifrequency: Data analysis and astroparticle problems, organized by the Department of Physics of the University of Perugia (Italy) on July 3-7, 2006. The necessarily limited time of the lessons forced to a drastic selection of the topics and, therefore, I have thought it was useful to complete the slides of the presentation with the notes you find in these few pages. These notes are a kind of ``link'' between the theoretical approach of the University lessons and the practice of the real use. During these years, I have seen that this material is useful for students that are beginning their thesis on research topics based on the use and the interpretation of data from X- and gamma-ray satellites. Therefore, I have thought to update the content of these notes, to translate them into English and to post on arXiv, in order to make them available to a larger public, hoping to give a useful help to other beginners. Since the public is basically composed of graduating students, I have assumed a well-grounded knowledge of basic astrophysics, the principles of instrumentation for physical sciences and the statistical analysis. Therefore, I have focused my notes on the practical issues and given some bibliographic references, just some advice, just to draw the attention on some points that are too much detailed for a university lesson. Nevertheless, the bibliography should be also a good starting point for those who want to further explore these topics.
We review 6 years of INTEGRAL observations of blazars, from Target-Of-Opportunity (TOO) to normal observations to coordinated campaigns, from the new and unexpected discoveries to the improvements in this research field. We also shortly review what is expected from INTEGRAL for the forthcoming years.
We report on an analysis of X- and $γ$-ray observations of PKS 1830-211, based on the long-term campaigns carried out by \emph{INTEGRAL} and COMPTEL. The \emph{INTEGRAL} data currently available present a $33σ$ significance detection in the 20-100 keV band, while the COMPTEL 6-years data provide a $5.2σ$ significance detection in the 1-3 MeV energy band. At hard X-rays, \emph{INTEGRAL} and supplementary \emph{SWIFT} observations show flux variability on timescales of months. At $γ$-rays, the source shows persistent emission over years. The hard X-ray spectrum is well represented by a power-law model, with $Γ\sim 1.3$ in the 20-250 keV band. This photon index is well consistent with the previous report of $Γ\sim 1.3$ obtained at $E > 3.5$ keV from the best fit of \emph{XMM-Newton} data with a broken power law model. The joint \emph{XMM-Newton}/\emph{INTEGRAL} spectrum presented here is then fit with a broken power-law model and the parameters are refined compared to the previous. The results show the photon index changes from $\sim 1.0$ to $\sim 1.3$ at a break energy $\sim 4$ keV. At MeV energies, the spectrum softens to $Γ\sim 2.2$. These results, together with the EGRET measurement at $E \ge 100$ MeV, constitute a broad-band spectrum containing the peak of the power output at MeV energies, similar to most high-luminosity $γ$-ray blazars. The measured spectral characterstics are then discussed in the framework of the gravitational lens effects.
The blazars 3C 454.3, PKS 0537-441 and PKS 2155-304 are traditionally known to be among the most active sources of this class. They emit at all frequencies, up to the gamma-rays, and are good probes of multiwavelength nuclear variability. The first two have also luminous broad emission line regions. We have recently monitored them with various facilities, including Swift and INTEGRAL, and have interpreted their variations with models of non-thermal radiation from a relativistic jet. In particular, we have tested for the first two sources the hypothesis that the variability is produced within the jet through internal shocks, i.e. collisions of relativistic plasma blobs. This allows a parameterization of all physical quantities as functions of the bulk Lorentz factor. We have made the critical assumption that every flaring episode is characterized by a fixed amount of energy. The model reproduces brilliantly the multiwavelength data and especially the gamma-ray spectra, when available. The model is not applicable to PKS 2155-304, the variability of which is caused by independent variations of few individual parameters.
Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite is uncovering large numbers of 20-100 keV "IGR" sources. We present results from Chandra, INTEGRAL, optical, and IR observations of 4 IGR sources: 3 sources in the Norma region of the Galaxy (IGR J16195-4945, IGR J16207-5129, and IGR J16167-4957) and one that is closer to the Galactic center (IGR J17195-4100). In all 4 cases, one relatively bright Chandra source is seen in the INTEGRAL error circle, and these are likely to be the soft X-ray counterparts of the IGR sources. They have hard 0.3-10 keV spectra with power-law photon indices of 0.5 to 1.1. While many previously studied IGR sources show high column densities, only IGR J16195-4945 has a column density that could be as high as 10^23 cm^-2. Using optical and IR sky survey catalogs and our own photometry, we have obtained identifications for all 4 sources. The J-band magnitudes are in the range 14.9-10.4, and we have used the optical/IR spectral energy distributions (SEDs) to constrain the nature of the sources. Blackbody components with temperature lower limits of >9400 K for IGR J16195-4945 and >18,000 K for IGR J16207-5129 indicate that these are very likely High-Mass X-ray Binaries (HMXBs). However, for IGR J16167-4957 and IGR J17195-4100, low extinction and the SEDs indicate later spectral types for the putative companions, indicating that these are not HMXBs.
In Spring 2005, the blazar 3C454.3 underwent a dramatic outburst at all wavelengths from mm to X-rays. This prompted INTEGRAL observations, accomplished in 15-18 May 2005. The source was detected by the INTEGRAL instruments from 3 to 200 keV in a bright state (~5 x 10E-10 cgs), at least a factor of 2-3 higher than previously observed. This is one of the brightest blazar detections achieved by INTEGRAL. During the 2.5 days of INTEGRAL monitoring, we detected a ~20% decrease in the hard X-rays (20-40 keV), indicating that we have sampled the decaying part of the flare. The decrease is less apparent in the soft X-rays (5-15 keV). The simultaneous optical variations are weakly correlated with those at soft X-rays, and not clearly correlated with those at hard X-rays. The spectral energy distribution exhibits two components, as typically seen in blazars, which can be modeled with synchrotron radiation and inverse Compton scattering occurring in a region external to the broad line region.
We report the discovery of a Narrow Line QSO located at about 1.3' from the Broad Line Radio Galaxy 3C445. The source,1WGA J2223.7-0206, although already revealed by ROSAT has never been optically identified previously. An XMM-Newton observation of 3C445 has allowed, for the first time, an accurate X-ray spectral study of 1WGA J2223.7-0206, revealing an ultra-soft spectrum and fast flux variations typical of Narrow Line AGN. The 0.2-10 keV spectrum is well represented by a power law (Gamma=2.5) plus a black body component (kT = 117 eV) absorbed by Galactic NH. About 80% of the X-ray flux is emitted below 2 keV. The 0.2-2 keV flux is observed to decrease by about a factor 1.6 in about 5000 s. The optical observations, triggered by the X-ray study, confirm the Narrow Line AGN nature of this source. The continuum is blue with typical AGN emission lines, pointing to a redshift z=0.46. The full width half maximum of H_beta is 2000 km/secand the flux rat io [OIII}]/H_beta=0.21. The optical luminosity (M_R=-23.2) and the point-like appearance in the optical images identify 1WGA J2223.7-0206 as a Narrow Line QSO. From the optical-UV-X-ray Spectral Energy Distribution we obtain a lower limit of the bolometric luminosity of 1WGA J2223.7-0206 (L_bol > 3 10^{45} erg/sec) implying, for accretion rates close to the Eddington limit, a black hole mass M_BH > 2.4 x 10^{7} M_{\odot}
Recent works, both theoretical and observational, have suggested that turbulence could play a non-negligible role in the broadening of emission lines in active galactic nuclei. The purpose of this note is to show how shock wave-turbulence interaction, under unsteady regime, can affect the broadening of emission lines.
In this paper, a meteoric plasma is analyzed from a physical viewpoint, with particular emphasis on its interaction with radio waves. The attention is drawn to some macroscopic characteristics of a meteoric plasma and it is shown that the electron-ion collision frequency is not negligible, as commonly thought.
On January 19, 1993, a very bright bolide (peak magnitude -23) crossed the sky of Northern Italy, ending with an explosion approximately over the town of Lugo (Emilia Romagna, Italy). The explosion (14 kton of energy) generated shock waves which were recorded by six local seismic stations. A reanalysis of the available data leads us to the hypothesis that the meteoroid was a porous carbonaceous chondrite, somehow similar in constitution to the asteroid 253 Mathilde.
This letter presents a new solution for the Tunguska event of June 30th, 1908. The solution has been obtained starting from seismic data, is in fair agreement with the observational evidence, and supports the asteroidal hypothesis for the origin of the Tunguska cosmic body. It is based on an improved model of the hypersonic flow around a small asteroid in the Earth's atmosphere.
The logic--linguistic structure of quantum physics is analysed. The role of formal systems and interpretations in the representation of nature is investigated. The problems of decidability, completeness, and consistency can affect quantum physics in different ways. Bohr's complementarity is of great interest,because it is a contradictory proposition. We shall see that the flowing of time prevents the birth of contradictions in nature, because it makes a cut between two different, but complementary aspects of the reality.
It is shown that the plasma, generated during an impact of a meteoroid with an artificial satellite, can produce electromagnetic radiation below the microwave frequency range. This interference is shown to exceed local noise sources and might disturb regular satellite operations.
The existence of large domains of antimatter is still an open question. Some space mission and experiments in the near future are expected to give reasonable answer to that question. Meanwhile, we can try to search for other signatures of the presence of antimatter. This paper presents a discussion about possible effects of the close encounter of stars and antistars. It is known that the accretion power can be higher in presence of antimatter, because of high-energy photons generated in annihilation, which result in a smaller radiation pressure. Therefore, the Eddington luminosity can reach higher values. Calculations of the gamma-ray flux above 100 MeV, and comparison with recent data from satellites, show a good agreement for certain sources. So, let's play some science-fiction!
It is known, from observational data recorded from airbursts, that small asteroids breakup at dynamical pressures lower than their mechanical strength. This means that actual theoretical models are inconsistent with observations. In this paper, we present a detailed discussion about data recorded from airbursts and about several theoretical models. We extend and improve a theory previously outlined for the fragmentation of small asteroids in the Earth atmosphere. The new condition for fragmentation is given by the shock wave-turbulence interaction, which results in sudden outburst of the dynamical pressure.