Beppo-SAX Observations of Galaxy Clusters

The high spatial resolution of the MECS experiment on board Beppo-SAX has encouraged a few scientists, including the author, to perform observations of galaxy clusters. Results from the analysis of the first few observed objects are encouraging. After having reviewed the Beppo-SAX observing program for galaxy clusters and referenced contributions to these proceedings by other authors on the same topic, I present results from the analysis of the Perseus cluster.Comment: 4 pages, 4 Postscript figures included. To appear in the proceedings of the ``Active X-ray Sky: Results from BeppoSAX and Rossi-XTE'

First Beppo-SAX results on AGN

In the following paper, some first Beppo-SAX results on AGN are presented. Main on-flight calibration features and observational properties are discussed at the light of possible future AGN studiesComment: 5 pages, Latex, 4 Postscript figures, `an-art.sty' included, to appear in Astronomische Nachrichten, vol.4, pag. 22

Relativistic generalization of formation and ion reflection conditions in electrostatic shocks

The theoretical model by Sorasio et al. (2006) for the steady state Mach number of electrostatic shocks formed in the interaction of two plasma slabs of arbitrary density and temperature is generalized for relativistic electron and non-relativistic ion temperatures. We find that the relativistic correction leads to lower Mach numbers, and as a consequence, ions are reflected with lower energies. The steady state bulk velocity of the downstream population is introduced as an additional parameter to describe the transition between the minimum and maximum Mach numbers in dependence of the initial density and temperature ratios. In order to transform the soliton-like solution in the upstream region into a shock, a population of reflected ions is considered and differences to a zero-ion temperature model are discussed

Timing, glitches and braking index of PSR B0540-69

We report a pulse-time history of PSR B0540$-$69 based on the analysis of an extended Data set including ASCA, BeppoSAX and RXTE observations spanning a time interval of about 8 years. This interval includes also the epoch of the glitch episode reported by Zhang et al. (2001). Our analysis shows the presence of a relevant timing noise and does not give a clear evidence of the glitch occurrence. We performed an accurate evaluation of the main timing parameters, $\nu$, $\dot{\nu}$ and $\ddot{\nu}$ and derived a mean braking index of $n=2.125\pm0.001$ quite different from the lower value found by Zhang et al. (2001), but in rather good agreement with other several values reported in the literature.Comment: 9 pages 5 figures, accepted by A&A, main journa

Discovery of X-rays from the supernova remnant G0.9+0.1

During the $BeppoSAX$ survey of the Galactic Center region, we have discovered X-ray emission from the central region of the supernova remnant G0.9+0.1. The high interstellar absorption (N_H about 3 times 10^{23} cm^-2) is consistent with a distance of order of 10 kpc and, correspondingly, an X-ray luminosity of about 10^{35} erg s^{-1}. Although we cannot completely rule out a thermal origin of the X-ray emission, its small angular extent (radius of about 2'), the good fit with a power law, the presence of a flat spectrum radio core, and the estimated SNR age of a few thousand years, favour the interpretation in terms of synchrotron emission powered by a young, energetic pulsar.Comment: 4 pages, 1 figure. Uses espcrc2.sty (included). To appear in The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P. Giommi and F. Fiore (eds.), Elsevier Science B.

CMB Observations: improvements of the performance of correlation radiometers by signal modulation and synchronous detection

Observation of the fine structures (anisotropies, polarization, spectral distortions) of the Cosmic Microwave Background (CMB) is hampered by instabilities, 1/f noise and asymmetries of the radiometers used to carry on the measurements. Addition of modulation and synchronous detection allows to increase the overall stability and the noise rejection of the radiometers used for CMB studies. In this paper we discuss the advantages this technique has when we try to detect CMB polarization. The behaviour of a two channel correlation receiver to which phase modulation and synchronous detection have been added is examined. Practical formulae for evaluating the improvements are presented.Comment: 18 pages, 3 figures, New Astronomy accepte

NLS1s and Sy1s: A comparison of ionized X-ray absorber properties

The first results from a systematic study of warm absorbers in NLS1s using BeppoSAX public archive data are presented here. We confirm ASCA results showing that a warm absorber, as modeled by two oxygen K-shell absorption edges, is less frequent in NLS1s than in broad line (BL) Sy1s (about 20 per cent versus about 50 per cent). However, our study suggests that the ionization state of NLS1s is not lower than that of BLS1s, as opposed to the ASCA-based results. The soft excess temperatures of our sample, when fitted with blackbody emission models, lie within a small range of values (about 0.02-0.15 keV in the rest frame) with no marked dependence on source luminosity. This is in agreement with ASCA-based findings for NLS1s and early results from IUE-ROSAT BL Sy1 observations.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho