Long-term variability of AGN at hard X-rays

Variability at all observed wavelengths is a distinctive property of AGN. Hard X-rays provide us with a view of the innermost regions of AGN, mostly unbiased by absorption along the line of sight. Swift/BAT offers the unique opportunity to follow, on time scales of days to years and with a regular sampling, the 14-195 keV emission of the largest AGN sample available up to date for this kind of investigation. We study the amplitude of the variations, and their dependence on sub-class and on energy, for a sample of 110 radio quiet and radio loud AGN selected from the BAT 58-month survey. About 80% of the AGN in the sample are found to exhibit significant variability on months to years time scales, radio loud sources being the most variable. The amplitude of the variations and their energy dependence are incompatible with variability being driven at hard X-rays by changes of the absorption column density. In general, the variations in the 14-24 and 35-100 keV bands are well correlated, suggesting a common origin of the variability across the BAT energy band. However, radio quiet AGN display on average 10% larger variations at 14-24 keV than at 35-100 keV and a softer-when-brighter behavior for most of the Seyfert galaxies with detectable spectral variability on month time scale. In addition, sources with harder spectra are found to be more variable than softer ones. These properties are generally consistent with a variable power law continuum, in flux and shape, pivoting at energies >~ 50 keV, to which a constant reflection component is superposed. When the same time scales are considered, the timing properties of AGN at hard X-rays are comparable to those at lower energies, with at least some of the differences possibly ascribable to components contributing differently in the two energy domains (e.g., reflection, absorption).

The 70 Month Swift-BAT All-Sky Hard X-Ray Survey

We present the catalog of sources detected in 70 months of observations of the BAT hard X-ray detector on the Swift gamma-ray burst observatory. The Swift-BAT 70 month survey has detected 1171 hard X-ray sources (more than twice as many sources as the previous 22 month survey) in the 14-195 keV band down to a significance level of 4.8 sigma, associated with 1210 counterparts. The 70 month Swift-BAT survey is the most sensitive and uniform hard X-ray all-sky survey and reaches a flux level of 1.03e-11 ergs/sec/cm2 over 50% of the sky and 1.34e-11 ergs/sec/cm2 over 90% of the sky. The majority of new sources in the 70 month survey continue to be AGN, with over 700 in the 70 month survey catalog. As part of this new edition of the Swift-BAT catalog, we also make available 8-channel spectra and monthly-sampled lightcurves for each object detected in the survey at the Swift-BAT 70 month website.

The 22-Month Swift-BAT All-Sky Hard X-ray Survey

We present the catalog of sources detected in the first 22 months of data from the hard X-ray survey (14--195 keV) conducted with the BAT coded mask imager on the swift satellite. The catalog contains 461 sources detected above the 4.8 sigma level with BAT. High angular resolution X-ray data for every source from Swift XRT or archival data have allowed associations to be made with known counterparts in other wavelength bands for over 97% of the detections, including the discovery of ~30 galaxies previously unknown as AGN and several new Galactic sources. A total of 266 of the sources are associated with Seyfert galaxies (median redshift z ~ 0.03) or blazars, with the majority of the remaining sources associated with X-ray binaries in our Galaxy. This ongoing survey is the first uniform all sky hard X-ray survey since HEAO-1 in 1977. Since the publication of the 9-month BAT survey we have increased the number of energy channels from 4 to 8 and have substantially increased the number of sources with accurate average spectra. The BAT 22-month catalog is the product of the most sensitive all-sky survey in the hard X-ray band, with a detection sensitivity (4.8 sigma) of 2.2e-11 erg/cm2/s (1 mCrab) over most of the sky in the 14--195 keV band.

On Active Galactic Nuclei as Sources of Ultra-High Energy Cosmic Rays

We measure the correlation between sky coordinates of the Swift BAT catalogue of active galactic nuclei with the arrival directions of the highest energy cosmic rays detected by the Auger Observatory. The statistically complete, hard X-ray catalogue helps to distinguish between AGN and other source candidates that follow the distribution of local large-scale structure. The positions of the full catalogue are marginally uncorrelated with the cosmic ray arrival directions, but when weighted by their hard X-ray flux, AGN within 100 Mpc are correlated at a significance level of 98 per cent. This correlation sharply decreases for sources beyond ~100 Mpc, suggestive of a GZK suppression. We discuss the implications for determining the mechanism that accelerates particles to these extreme energies in excess of 10^19 eV.

Classical and quantum Coulomb crystals

Strong correlation effects in classical and quantum plasmas are discussed. In particular, Coulomb (Wigner) crystallization phenomena are reviewed focusing on one-component non-neutral plasmas in traps and on macroscopic two-component neutral plasmas. The conditions for crystal formation in terms of critical values of the coupling parameters and the distance fluctuations and the phase diagram of Coulomb crystals are discussed.