BeppoSAX Observations of Mkn 421: clues on the particle acceleration ?

Mkn 421 was repeatedly observed with BeppoSAX in 1997-1998. We present highlights of the results of the thorough temporal and spectral analysis discussed by Fossati et al. (1999) and Maraschi et al. (1999), focusing on the flare of April 1998, which was simultaneously observed also at TeV energies. The detailed study of the flare in different energy bands reveals a few very important new results: (a) hard photons lag the soft ones by 2-3 ks *a behavior opposite to what is normally found in High energy peak BL Lacs X-ray spectra*; (b) the flux decay of the flare can be intrinsically achromatic if a stationary underlying emission component is present. Moreover the spectral evolution during the flare has been followed by extracting X-ray spectra on few ks intervals, allowing to detect for the first time the peak of the synchrotron component shifting to higher energies during the rising phase, and then receding. The spectral analysis confirms the delay in the flare at the higher energies, as above a few keV the spectrum changes only after the peak of the outburst has occurred. The spectral and temporal information obtained challenge the simplest models currently adopted for the (synchrotron) emission and most importantly provide clues on the particle acceleration process. A theoretical picture accounting for all the observational constraints is discussed, where electrons are injected at low energies and then progressively accelerated during the development of the flare.Comment: 5 pages, LaTeX, uses aipproc.sty, 3 PostScript figures, to appear in the Proceedings of the "Fifth Compton Symposium", held in Portsmouth (NH), 1999 Septembe

Regional and international market integration of a small open economy

This paper studies the relationship between a set of commodity prices in a small open economy like Uruguay and the corresponding international and regional prices. The empirical methodology used is the multivariate cointegration procedure based on maximum likelihood methods introduced by Johansen (1988) as well as estimations of half-life persistence indicators. In the case of cereals, the evidence suggests strong market integration between domestic and regional markets and, to some extent, also to international markets. Therefore, directly or indirectly, domestic prices are connected with the efficient price signal. Results for beef indicate strong market integration between the domestic market and the regional market, which is not so well connected with international markets. Thus, domestic price appears to be linked to a regional price that is not linked to the efficient price signal.commodity prices, law of one price, market integration, cointegration

Six years of BeppoSAX observations of blazars: a spectral catalog

We present a spectral catalog for blazars based on the BeppoSAX archive. The sample includes 44 High-energy peaked BL Lacs (HBLs), 14 Low-energy peaked BL Lacs (LBLs), and 28 Flat Spectrum Radio Quasars (FSRQs). A total of 168 LECS, MECS, and PDS spectra were analyzed, corresponding to observations taken in the period 1996--2002. The 0.1--50 keV continuum of LBLs and FSRQs is generally fitted by a single power law with Galactic column density. A minority of the observations of LBLs (25%) and FSRQs (15%) is best fitted by more complex models like the broken power law or the continuously curved parabola. These latter models provide also the best description for half of the HBL spectra. Complex models are more frequently required for sources with fluxes F_{2-10 keV} > 10^-11 cm-2 s-1, corresponding to spectra with higher signal-to-noise ratio. As a result, considering sources with flux above this threshold, the percentage of spectra requiring those models increases for all the classes. We note that there is a net separation of X-ray spectral properties between HBLs on one side, and LBLs and FSRQs on the other, the distinction between LBLs and FSRQs is more blurry. This is most likely related to ambiguities in the optical classification of the two classes.Comment: 6 pages, 4 figures, 7 tables. Accepted for publication in A&

A probable pre-main sequence chemically peculiar star in the open cluster Stock 16

We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Delta-a photometric observations suggest being a chemically peculiar (CP) star. We used spectral synthesis to perform a detailed abundance analysis obtaining an effective temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence showing the star is most likely a member of the young Stock 16 open cluster (age 3-8 Myr). The probable cluster membership, the star's position in the Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun, depending upon the adopted spectroscopic or photometric data results. Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement with that of the cluster. Because the star's chemical abundance pattern resembles well that known of main sequence CP metallic line (Am) stars, the object sets important constraints to the diffusion theory. Additional spectroscopic and spectropolarimetric data allowed us to conclude that the object is probably a single non-magnetic star.Comment: Accepted for publication in MNRAS; 8 pages, 5 figures, 1 tabl

Ram Pressure Stripping in High-Density Environments

Galaxies living in rich environments are suffering different perturbations able to drastically affect their evolution. Among these, ram pressure stripping, i.e. the pressure exerted by the hot and dense intracluster medium (ICM) on galaxies moving at high velocity within the cluster gravitational potential well, is a key process able to remove their interstellar medium (ISM) and quench their activity of star formation. This review is aimed at describing this physical mechanism in different environments, from rich clusters of galaxies to loose and compact groups. We summarise the effects of this perturbing process on the baryonic components of galaxies, from the different gas phases (cold atomic and molecular, ionised, hot) to magnetic fields and cosmic rays, and describe their induced effects on the different stellar populations, with a particular attention to its role in the quenching episode generally observed in high density environments. We also discuss on the possible fate of the stripped material once removed from the perturbed galaxies and mixed with the ICM, and we try to estimate its contribution to the pollution of the surrounding environment. Finally, combining the results of local and high redshift observations with the prediction of tuned models and simulations, we try to quantify the importance of this process on the evolution of galaxies of different mass, from dwarfs to giants, in various environments and at different epochs.Comment: Invited review for The Astronomy and Astrophysics Revie

Signs of strong Na and K absorption in the transmission spectrum of WASP-103b

Context: Transmission spectroscopy has become a prominent tool for characterizing the atmospheric properties on close-in transiting planets. Recent observations have revealed a remarkable diversity in exoplanet spectra, which show absorption signatures of Na, K and $\mathrm{H_2O}$, in some cases partially or fully attenuated by atmospheric aerosols. Aerosols (clouds and hazes) themselves have been detected in the transmission spectra of several planets thanks to wavelength-dependent slopes caused by the particles' scattering properties. Aims: We present an optical 550 - 960 nm transmission spectrum of the extremely irradiated hot Jupiter WASP-103b, one of the hottest (2500 K) and most massive (1.5 $M_J$) planets yet to be studied with this technique. WASP-103b orbits its star at a separation of less than 1.2 times the Roche limit and is predicted to be strongly tidally distorted. Methods: We have used Gemini/GMOS to obtain multi-object spectroscopy hroughout three transits of WASP-103b. We used relative spectrophotometry and bin sizes between 20 and 2 nm to infer the planet's transmission spectrum. Results: We find that WASP-103b shows increased absorption in the cores of the alkali (Na, K) line features. We do not confirm the presence of any strong scattering slope as previously suggested, pointing towards a clear atmosphere for the highly irradiated, massive exoplanet WASP-103b. We constrain the upper boundary of any potential cloud deck to reside at pressure levels above 0.01 bar. This finding is in line with previous studies on cloud occurrence on exoplanets which find that clouds dominate the transmission spectra of cool, low surface gravity planets while hot, high surface gravity planets are either cloud-free, or possess clouds located below the altitudes probed by transmission spectra.Comment: Accepted for publication in A&

fatigue crack propagation in a helicopter component subjected to impact damage

Abstract Damage tolerant methodology is increasingly used in aeronautical components, especially due the fact that the Aviation Regulation requires such an assessment in case an accidental damage occurs. At present, there is a strong and actual interest in applying such procedures to helicopter components that are subjected to high frequency cyclic loads. In this paper, an investigation on a damaged transmission shaft for a tail rotor transmission of an actual helicopter has been carried out focusing on the fatigue crack propagation. A complete sequence of experimental tests was performed in order to create an actual ballistic damage and to subsequently check the damage tolerant behaviour. The shaft was damaged by oblique ballistic impact and was subsequently subjected to torsional fatigue loading. During the fatigue cycles several cracks propagated from the ballistic damages. Both of these steps (impact and fatigue loading) were also simulated by a complex modelling approach based on Finite Element Models and fracture mechanics theory. The comparison between the experimental and numerical results shows a good agreement but it underlines the need for a very refined modelling technique capable to replicate all the features associated with the damage in order to reliably simulate the subsequent propagation phase