arXiv subjects

L. Foschini

Publications and source records attributed to L. Foschini.

138 records · Page 8Linked to original sources

arXiv2003

Search for relativistic beaming in ultraluminous X-ray sources

The nature of the ultraluminous X-ray sources (ULX) is still to be understood. Several hypotheses have been suggested to explain the high X-ray luminosity: stellar mass black holes with emission collimated by relativistic effects or anisotropies in the accretion disk, intermediate mass black holes, young supernovae remnants, background active galactic nuclei. To discriminate among the above hypotheses, the search for relativistic effects can be a valuable "pathfinder". Here we propose a list of ULX candidates suitable to show relativistic beaming

astro-ph↗

arXiv2002

BL Lac Identification for the Ultraluminous X-ray Source Observed in the Direction of NGC 4698

We report the identification of the optical and radio counterparts of the ultraluminous X-ray (ULX) source XMMU J124825.9+083020 (NGC4698-ULX1). The optical spectrum taken with the VLT yields a redshift of z=0.43, which implies that the ULX is not associated with the nearby galaxy NGC4698. The spectral energy distribution calculated from the available data indicates that the source is likely to be a BL Lac object. The possible synchrotron peak at X-ray energies suggests that this source may be a gamma-ray emitter.

astro-ph↗

arXiv2002

Search for ultraluminous X-ray sources in nearby galaxies

Little is presently known about the nature of ultraluminous X-ray sources (ULX). Different hypotheses have been proposed to explain their properties: intermediate-mass BHs, Kerr BHs, young SNR, or background AGN. Some of the current problems and open questions in this research field are here reviewed.

astro-ph↗

arXiv2002

XMM-NEWTON Observation of the Seyfert 2 Galaxy NGC 4138

The XMM-Newton data presented here are the first X-ray observation of the Seyfert 2 galaxy NGC4138. Although the galaxy has been pointed by ROSAT-HRI, it was not detected, with a flux upper limit of about 1.1x10^-13 erg cm^-2 s^-1 in the 0.2-2.4 keV energy band. XMM-Newton performed the observation on 26 November 2001. The source is detected for the first time in X-rays with F[0.2-2.4]=1.0x10^-13 erg cm^-2 s^-1, in agreement with the upper limit of ROSAT. The source spectrum is typical of Seyfert 2 galaxies. We find heavy obscuration (N_H about 8x10^22 cm^-2) and a flat photon index (1.6). The source intrinsic luminosity is about 5x10^41 erg/s in the 0.5-10 keV energy band.

astro-ph↗

arXiv2002

XMM-Newton observations of ultraluminous X-ray sources in nearby galaxies

An XMM-Newton study of ultraluminous X-ray sources (ULX) has been performed in a sample of 10 nearby Seyfert galaxies. Eighteen ULX have been found with positional uncertainty of about 4". The large collecting area of XMM-Newton makes the statistics sufficient to perform spectral fitting with simple models in 8 cases. The main results of the present minisurvey strengthen the theory that the ULX could be accreting black holes in hard or soft state. In some cases, the contribution of the ULX to the overall X-ray flux appears to be dominant with respect to that of the active nucleus. In addition, 6 ULX present probable counterparts at other wavelengths (optical/infrared, radio). A multiwavelength observing strategy is required to better assess the nature of these sources.

astro-ph↗

arXiv2002

IBIS/PICsIT Data and Analysis

The imager IBIS on board INTEGRAL is composed of two detector planes: ISGRI (15 keV - 1 MeV) and PICsIT (170 keV - 10 MeV). Here we describe the data structure of PICsIT and the instrument specific software, including the standard scientific analysis. Some examples of shadowgrams and spectra are shown, by using data collected during the End-to-End Tests of January 2002.

astro-ph↗

arXiv2002

First Results from a XMM-Newton Survey of a Distance-Limited (D<22 Mpc) Sample of Seyfert Galaxies: I- the Agns

We report here preliminary results from a survey of nearby Seyfert galaxies using the EPIC CCDs on board XMM-Newton. The total sample consists of 28 Seyfert galaxies, and constitute a well-defined, complete (B<12.5 mag), and volume-limited (D<22 Mpc) sample of Seyfert galaxies in the northern (Delta > 0 deg.) hemisphere. The survey has been initiated in June, 2001, and we report here the results for the 6 objects analyzed so far, namely: NGC3185, NGC3486, NGC3941, NGC4138, NGC4565, and NGC5033. The main goal of this survey is to obtain a better and unbiased understanding of the ``typical'' Seyfert X-ray spectrum (e.g. the distribution of their absorption column density) in the local Universe. This is crucial to verify the predictions and, thus, to validate unified models, and is a fundamental parameter of synthesis models for the X-ray background. A companion poster (paper II: L. Foschini et al., these proceedings) illustrates how this survey will also allow a comprehensive spectral study of the brightest (highest-luminosity) off-nuclear sources in the galaxies.

astro-ph↗

arXiv2002

First Results from a XMM-Newton Survey of a Distance-Limited (D < 22 Mpc) Sample of Seyfert Galaxies. II - The Galactic Serendipitous Sources

We present preliminary results from a study with XMM-Newton of the galactic serendipitous sources in a sample of 28 nearby Seyfert galaxies (with D < 22 Mpc). We concentrate here on a subset of four galaxies, namely: NGC3185, NGC3486, NGC3941, and NGC4565. In these galaxies we found six ultraluminous X-ray source (ULX). The large collecting area of XMM-Newton makes the statistics sufficient to perform spectral fitting with simple models. We shortly discuss the results obtained so far.

astro-ph↗

arXiv2001

On the meteor height from forward scatter radio observations

It is known from theory that, by means of a plasma physics approach, it is possible to obtain a simple formula to calculate the approximate height of a meteor (Foschini, 1999). This formula can be used in case of forward scatter of radio waves and has the advantage that it does not depend on the diffusion coefficient. On the other hand, it is possible to apply the formula to a particular type of meteor only (overdense meteor type I), which is a small fraction of the total number observed. We have carried out a statistical analysis of several radio echoes from meteor showers recorded during last years by a radio observer located in Belgium. Results are compared and discussed with those obtained with other methods and available in literature.

astro-ph↗

arXiv2001

A space charge model for electrophonic bursters

The sounds accompanying electrophonic burster meteors are characteristically described as being akin to short duration ``pops'' and staccato--like ``clicks''. As a phenomenon distinct from the enduring electrophonic sounds that occasionally accompany the passage and ablation of large meteoroids in the Earth's lower atmosphere, the bursters have proved stubbornly difficult to explain. A straightforward calculation demonstrates that in contradistinction to the enduring electrophonic sounds, the electrophonic bursters are not generated as a consequence of interactions between the meteoroid ablation plasma and the Earth's geomagnetic field. Here we present a novel and hitherto unrecorded model for the generation of short--duration pulses in an observer's local electrostatic field. Our model is developed according to the generation of a strong electric field across a shock wave propagating in a plasma. In this sense, the electrophonic bursters are associated with the catastrophic disruption of large meteoroids in the Earth's atmosphere. We develop an equation for the description of the electric field strength in terms of the electron temperature and the electron volume density. Also, by linking the electron line density to a meteor's absolute visual magnitude, we obtain a lower limit to the visual magnitude of electrophonic burster meteors of $M_{\mathrm{v}}\approx -6.6$, in good agreement with the available observations.

astro-ph↗

arXiv2001

Gamma-Ray Imaging with the Coded Mask IBIS Telescope

The IBIS telescope onboard INTEGRAL, the ESA gamma-ray space mission to be launched in 2002, is a soft gamma-ray (20 keV - 10 MeV) device based on a coded aperture imaging system. We describe here basic concepts of coded masks, the imaging system of the IBIS telescope, and the standard data analysis procedures to reconstruct sky images. This analysis includes, for both the low-energy detector layer (ISGRI) and the high energy layer (PICSIT), iterative procedures which decode recorded shadowgrams, search for and locate sources, clean for secondary lobes, and then rotate and compose sky images. These procedures will be implemented in the Quick Look and Standard Analysis of the INTEGRAL Science Data Center (ISDC) as IBIS Instrument Specific Software.

astro-ph↗

arXiv2001

PICsIM - the INTEGRAL/IBIS/PICsIT Observation Simulation Tool for Prototype Software Evaluation

The INTEGRAL satellite is an observatory-class gamma-ray telescope due for launch in early 2002. It comprises two main instruments, one optimised for imaging (IBIS) and the other for spectroscopy (SPI). The PICsIT telescope is the high energy (150 keV - 10 MeV) plane of the IBIS imager and consists of 8 individual modules of 512 detection elements. The modules are arranged in a 4 x 2 pattern, while the pixels are in a 16 x 32 array. This layout, which includes a dead area equivalent to one pixel width between each module, together with the event selection procedure, which (in standard mode) does not allow the identification of coincidences between separate modules, leads to a non-uniformity of the background which is significantly different for single-site events and for multiple energy deposits. Other sources of background variations range from the separate low energy detector, situated immediately above the PICsIT plane, to the large mass of the SPI telescope at a short distance to one side. The algorithms for performing all the imaging and spectral deconvolution for PICsIT are currently being produced for delivery to the INTEGRAL Science Data Centre. In order to maximise the information which may be extracted from the PICsIT data, we have designed a prototyping environment which consists of a GUI to a highly structured and modular set of procedures which allows the easy simulation of observations from the data collection phase through to the final image production and analysis.

astro-ph↗