The last Gift of BeppoSAX: PDS Observations of the two Blazars 1ES 0507-040 and PKS 1229-021

Towards the end of the BeppoSAX mission, the only operated Narrow Field Instrument was the PDS, which covers the energy range 13-300 keV. Two blazars, 1ES 0507-040 (z=0.304) and PKS 1229-021 (z= 1.045), suitably located in the sky for BeppoSAX pointing, were observed for about 2 days each in Spring 2002 with the PDS and detected up to 50 keV. 1ES0507-040 had been already observed by the BeppoSAX NFIs at an earlier epoch for a much shorter time. We have re-analysed those data as well, and identified a possible contamination problem in the PDS spectrum. We present our recent PDS data on both sources, combined with the previous BeppoSAX data and with non-simultaneous observations at other frequencies. The derived Spectral Energy Distributions allow us to discuss the origin of the high energy component.Comment: 4 pages, 6 figures, poster presented at the symposium: The Restless High-Energy Universe, Amsterdam, May 200

Spectral Evolution of PKS 2155-304 observed with BeppoSAX during an Active Gamma-ray Phase

We present the results of BeppoSAX observations of PKS 2155-304 during an intense gamma-ray flare. The source was in a high X-ray state. A temporal analysis of the data reveals a tendency of the amplitude of variations to increase with energy, and the presence of a soft lag with a timescale of the order 10^3 s. A curved continuum spectrum, with no evidence of spectral features, extends up to ~50 keV, while there is indication of a flatter component emerging at higher energies, consistent with the interpretation of the broad band spectral energy distribution (SED) as due to synchrotron self-Compton (SSC) emission from a single region. Notably, the fitting of the SED with such a model is consistent with an interpretation of the detected soft lag as due to radiative cooling, supporting the idea that radiation losses play an important role in variability. The observed shifts of the SED peaks between the lowest and highest flux levels can be accounted for by an increase of the break energy in the relativistic particle spectrum. The model predicts emission at TeV energies in good agreement with the recently reported detection.Comment: 36 pages (8 figures), Latex with AAS macros, etc), accepted for publication on Astrophysical Journa

Development of Sintered Fiber Nickel Electrodes for Aerospace Batteries

The nickel electrode is the specific energy limiting component in nickel battery systems. A concerted effort is currently underway to improve NiH2 performance while decreasing system cost. Increased performance with electrode specific energy (mAh/g) is the major goal of this effort. However, cost reduction is also an important part of the overall program, achieved by reducing the electrode weight. A lightweight, high energy density, nickel electrode is being, developed based on a highly porous, sintered fiber, nickel substrate. This developing technology has many applications, but is highly, applicable to the military and aerospace industries

Search for gravitational lens candidates in the XMM-LSS/CFHTLS common field

Our aim was to identify gravitational lens candidates among some 5500 optical counterparts of the X-ray point-like sources in the medium-deep ~11 sq. deg. XMM-LSS survey. We have visually inspected the optical counterparts of each QSOs/AGN using CFHTLS T006 images. We have selected compact pairs and groups of sources which could be multiply imaged QSO/AGN. We have measured the colors and characterized the morphological types of the selected sources using the multiple PSF fitting technique. We found three good gravitational lens candidates: J021511.4-034306, J022234.3-031616 and J022607.0-040301 which consist of pairs of point-like sources having similar colors. On the basis of a color-color diagram and X-ray properties we could verify that all these sources are good QSO/AGN candidates rather than stars. Additional secondary gravitational lens candidates are also reported.Comment: 6 pages, 3 figures, 1 table, Accepted for publication in MNRA

Broad Band X-ray Spectra of M31 Sources with BeppoSAX

We present the first spectral study of the X-ray emitting stellar sources in M31 in the energy band from 0.1 to 10 keV. We find that the globular cluster sources have spectral characteristics consistent with those of the Milky Way object, namely that the spectrum can be described by a thermal model with 6-20 keV from 2 to 10 keV. Evidence of high absorption in some of these sources is most likely an indication that they lie in or behind the HI ring in the disk of the galaxy. We also find one peculiar globular cluster source, with spectral characteristics more typically associated with either High Mass X-ray Binaries or black hole candidates. We therefore suggest that either the source has been wrongly identified with a globular cluster or that the system contains a Black Hole. We confirm earlier report that the spectrum of the bulge of M31 is consistent with the superposition of many LMXB spectra. It is likely that a large fraction of the 15-30 keV detection obtained from the PDS instrument is associated with the bulge, thus extending the spectral data for this complex of sources up to 30 keV. The high energy part of the spectrum can be parameterized with typical LMXB spectra, while at low energies an additional component is required.Comment: Accepted for publication in A&A, main journa

X-ray AGN in the XMM-LSS galaxy clusters: no evidence of AGN suppression

We present a study of the overdensity of X-ray selected AGN in 33 galaxy clusters in the XMM-LSS field, up to redhift z=1.05. Previous studies have shown that the presence of X-ray selected AGN in rich galaxy clusters is suppressed. In the current study we investigate the occurrence of X-ray selected AGN in low and moderate X-ray luminosity galaxy clusters. Due to the wide contiguous XMM-LSS survey area we are able to extend the study to the cluster outskirts. We therefore determine the projected overdensity of X-ray point-like sources out to 6r_{500} radius. To provide robust statistical results we also use a stacking analysis of the cluster projected overdensities. We investigate whether the observed X-ray overdensities are to be expected by estimating also the corresponding optical galaxy overdensities. We find a positive X-ray projected overdensity at the first radial bin, which is however of the same amplitude as that of optical galaxies. Therefore, no suppression of X-ray AGN activity with respect to the field is found, implying that the mechanisms responsible for the suppression are not so effective in lower density environments. After a drop to roughly the background level between 2 and 3r_{500}, the X-ray overdensity exhibits a rise at larger radii, significantly larger than the corresponding optical overdensity. Finally, using redshift information of all optical counterparts, we derive the spatial overdensity profile of the clusters. We find that the agreement between X-ray and optical overdensities in the first radial bin is also suggested in the 3-dimensional analysis. However, we argue that the X-ray overdensity "bump" at larger radial distance is probably a result of flux boosting by gravitational lensing of background QSOs. For high redshift clusters an enhancement of X-ray AGN activity in their outskirts is still possible.Comment: 16 pages. Accepted for publication in A&

Progress in understanding Blazars from BeppoSAX observations

Results obtained with BeppoSAX observations of blazars within various collaborative programs are presented. The spectral similarity "paradigm", whereby the spectral energy distributions of blazars follow a sequence, leading to a unified view of the whole population, is briefly illustrated. We concentrate on recent observations of flares and associated spectral variability for three objects at the "blue" end of the spectral sequence, namely PKS 2155-304, Mkn 421 and Mkn 501. The results are discussed in terms of a general analytic synchrotron self-Compton interpretation of the overall spectrum. The physical parameters of the quasi-stationary emission region can be derived with some confidence, while the variability mechanism(s) must be complex.Comment: 10 pages, 8 figures, to be published in the Proceedings of the 32nd COSPAR Meeting, Nagoya, 12-19 July 199