AGN variability at hard X-rays

We present preliminary results on the variability properties of AGN above 20 keV in order to show the potential of the INTEGRAL IBIS/ISGRI and Swift/BAT instruments for hard X-ray timing analysis of AGN. The 15-50 keV light curves of 36 AGN observed by BAT during 5 years show significantly larger variations when the blazar population is considered (average normalized excess variance = 0.25) with respect to the Seyfert one (average normalized excess variance = 0.09). The hard X-ray luminosity is found to be anti-correlated to the variability amplitude in Seyfert galaxies and correlated to the black hole mass, confirming previous findings obtained with different AGN hard X-ray samples. We also present results on the Seyfert 1 galaxy IC 4329A, as an example of spectral variability study with INTEGRAL/ISGRI data. The position of the high-energy cut-off of this source is found to have varied during the INTEGRAL observations, pointing to a change of temperature of the Comptonising medium. For several bright Seyfert galaxies, a considerable amount of INTEGRAL data have already been accumulated and are publicly available, allowing detailed spectral variability studies at hard X-rays.Comment: 6 pages, 6 figures. Accepted for publication on PoS (contribution PoS(extremesky2009)031), proceedings of "The Extreme sky: Sampling the Universe above 10 keV", held in Otranto (Italy) in October 200

Compton processes in the bright AGN MCG+8-11-11

We present preliminary results on the hard X-ray emission properties of the Seyfert 1.5 galaxy MCG+8-11-11 as observed by INTEGRAL and SWIFT. All the INTEGRAL IBIS/ISGRI data available up to October 2009 have been analyzed together with two SWIFT/XRT snapshot observations performed in August and October 2009, quasi-simultaneously to INTEGRAL pointed observations of MCG+8-11-11. No correlation is observed between the hard X-ray flux and the spectral slope, while the position of the high-energy cut-off is found to have varied during the INTEGRAL observations. This points to a change in the temperature of the Comptonising medium from a minimum value of kT = 30-50 keV to values larger than 100-150 keV. There is no significant detection of Compton reflection, with a 3 sigma upper limit of R < 0.2, and no line has been detected at 112 keV, as previously claimed from HEAT observations (112 keV flux F < 2.4e-4 ph/cm^2/s). The variability behaviour of MCG+8-11-11 is found to be similar to that shown by IC 4329A, with different temperatures of the electron plasma for similar flux levels of the source, while other bright Seyfert galaxies present different variability patterns at hard X-rays, with spectral changes correlated to flux variations (e.g. NGC 4151).Comment: 6 pages, 4 figures. Accepted for publication on PoS (contribution PoS(INTEGRAL 2010)077), proceedings of the 8th INTEGRAL Workshop "The Restless Gamma-ray Universe" (September 2010, Dublin, Ireland

Investigating mathematics in Scotland and the United States

This paper presents the results of an initial investigation on how educators from two different educational systems engaged in mathematics calculations. The study explored the nature of the educators' solution strategies and the extent to which these strategies adhered to standard taught algorithms or more non-traditional procedures. Our future studies hope to provide more evidence of our beliefs that teachers who only know or use traditional algorithms are not readily able to assist students with developing more sense-making strategies that not only are more efficient but also reflect flexible thinking

Composition of the nuclear periphery from antiproton absorption

Thirteen targets with mass numbers from 58 to 238 were irradiated with the antiproton beam from the Low Energy Antiproton Ring facility at CERN leading to the formation of antiprotonic atoms of these heavy elements. The antiproton capture at the end of an atomic cascade results in the production of more or less excited residual nuclei. The targets were selected with the criterion that both reaction products with one nucleon less than the proton and neutron number of the target be radioactive. The yield of these radioactive products after stopped-antiproton annihilation was determined using gamma-ray spectroscopy techniques. This yield is related to the proton and neutron density in the target nucleus at a radial distance corresponding to the antiproton annihilation site. The experimental data clearly indicate the existence of a neutron-rich nuclear periphery, a "neutron halo", strongly correlated with the target neutron separation energy Bn and observed for targets with Bn < 10 MeV. For two-target nuclei 106Cd and 144Sm, with larger neutron binding energies, a proton-rich nuclear periphery was observed. Most of the experimental data are in reasonable agreement with calculations based on current antiproton-nucleus and pion-nucleus interaction potentials and on nuclear densities deduced with the help of the Hartree-Fock-Bogoliubov approach. This approach was, however, unable to account for the 106Cd and 144Sm results.Comment: Latex (RevTeX,aps style), 13 pages + 12 Postscript figure

Gold fragmentation induced by stopped antiprotons

A natural gold target was irradiated with the antiproton beam from the Low Energy Antiproton Ring at CERN. Antiprotons of 200 MeV/c momentum were stopped in a thick target, products of their annihilations on Au nuclei were detected using the off-line gamma-ray spectroscopy method. In total, yields for 114 residual nuclei were determined, providing a data set to deduce the complete mass and charge distribution of all products with A > 20 from a fitting procedure. The contribution of evaporation and fission decay modes to the total reaction cross section as well as the mean mass loss were estimated. The fission probability for Au absorbing antiprotons at rest was determined to be equal to (3.8+-0.5)%, in good agreement with an estimation derived using other techniques. The mass-charge yield distribution was compared with the results obtained for proton and pion induced gold fragmentation. On the average, the energy released in pbar annihilation is similar to that introduced by ~ 1 GeV protons. However, compared to proton bombardment products, the yield distribution of antiproton absorption residues in the N-Z plane is clearly distinct. The data for antiprotons exhibit also a substantial influence of odd-even and shell effects.Comment: 14 pages, 9 figures, Revtex 4, to be published in Physical Review

Historical Origins of Environment Sustainability in the German Chemical Industry, 1950s-1980s

This working paper examines the growth of corporate environmentalism in the West German chemical industry between the 1950s and the 1980s. It focuses on two companies, Bayer and Henkel and traces the evolution of their environmental strategies in response to growing evidence of pollution and resulting political pressures. Although German business has been regarded as pioneering corporate environmentalism, this study reveals major commonalities between the German and American chemical industries until the 1970s, when the two German firms diverged from their American counterparts in using public relations strategies not only to contain fallout from criticism, but also as opportunities for changes in corporate culture. The working paper finds no evidence for variety of capitalism explanations why German firms should have been early in their sustainability strategies, partly because of the importance of regional as opposed to national influences, but the study is supportive of organizational sociology theories which have identified the importance of visibility in corporate green strategies

INTEGRAL observations of V0332+53 in outburst

We present the analysis of a 100ksec Integral(3-100kev) observation of the transient X-ray pulsar V0332+53 inoutburst. The source is pulsating at P=4.3751+/-0.0002s with a clear double pulse from 6 kev to 60 kev. The average flux was ~550mCrab between 20 kev and 60 kev. We modeled the broad band continuum from 5 kev to 100 kev with a power-law modified by an exponential cut off. We observe three cyclotron lines: the fundamental line at 24.9+/-0.1 kev, the first harmonic at 50.5+/-0.1 kev as well as the second harmonic at71.7+/-0.8 kev, thus confirming the discovery of the harmonic lines by Coburn et al. (2005) in RXTE data.Comment: 4 pages, 3 figures. Accepted for publication in A&A Letter

The Second INTEGRAL AGN Catalogue

The INTEGRAL mission provides a large data set for studying the hard X-ray properties of AGN and allows testing of the unified scheme for AGN. We present analysis of INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly detected by INTEGRAL above 20 keV. The data analysed here allow a significant spectral extraction on 148 objects and an optical variability study of 57 AGN. The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert~2 galaxies are found to be consistent within the uncertainties, whereas higher cut-off energies and lower luminosities are measured for the more absorbed / type 2 AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent with those of Seyfert 1. When applying a Compton reflection model, the underlying continua appear the same in Seyfert 1 and 2 with photon index 2, and the reflection strength is about R = 1, when assuming different inclination angles. A significant correlation is found between the hard X-ray and optical luminosity and the mass of the central black hole in the sense that the more luminous objects appear to be more massive. There is also a general trend toward the absorbed sources and type 2 AGN having lower Eddington ratios. The black holemass appears to form a fundamental plane together with the optical and X-ray luminosity of the form Lv being proportional to Lx^0.6 M^0.2, similar to that found between radio luminosity Lr, Lx, and M. The unified model for Seyfert galaxies seems to hold, showing in hard X-rays that the central engine is the same in Seyfert 1 and 2, but seen under different inclination angles and absorption. (Abridged)Comment: 26 pages, 16 figures, accepted for publication in A&A. Corrections by language editor included in version

The reprocessing features in the X-ray spectrum of the NELG MCG-5-23-16

We present results from the spectral analysis of the Seyfert 1.9 galaxy MCG-5-23-16, based on ASCA, BeppoSAX, Chandra and XMM-Newton observations. The spectrum of this object shows a complex iron Kalpha emission line, which is best modeled by a superposition of a narrow and a broad (possibly relativistic) iron line, together with a Compton reflection component. Comparing results from all (six) available observations, we do not find any significant variation in the flux of both line components. The moderate flux continuum variability (about 25% difference between the brightest and faintest states), however, does not permit us to infer much about the location of the line-emitting material. The amount of Compton reflection is lower than expected from the total iron line EW, implying either an iron overabundance or that one of the two line components (most likely the narrow one) originates in Compton-thin matter.Comment: Accepted for publication in A&

Multiwavelength campaign on Mrk 509 XII. Broad band spectral analysis

(Abridged) The simultaneous UV to X-rays/gamma rays data obtained during the multi-wavelength XMM/INTEGRAL campaign on the Seyfert 1 Mrk 509 are used in this paper and tested against physically motivated broad band models. Each observation has been fitted with a realistic thermal comptonisation model for the continuum emission. Prompted by the correlation between the UV and soft X-ray flux, we use a thermal comptonisation component for the soft X-ray excess. The UV to X-rays/gamma-rays emission of Mrk 509 can be well fitted by these components. The presence of a relatively hard high-energy spectrum points to the existence of a hot (kT~100 keV), optically-thin (tau~0.5) corona producing the primary continuum. On the contrary, the soft X-ray component requires a warm (kT~1 keV), optically-thick (tau~15) plasma. Estimates of the amplification ratio for this warm plasma support a configuration close to the "theoretical" configuration of a slab corona above a passive disk. An interesting consequence is the weak luminosity-dependence of its emission, a possible explanation of the roughly constant spectral shape of the soft X-ray excess seen in AGNs. The temperature (~ 3 eV) and flux of the soft-photon field entering and cooling the warm plasma suggests that it covers the accretion disk down to a transition radius $R_{tr}$ of 10-20 $R_g$. This plasma could be the warm upper layer of the accretion disk. On the contrary the hot corona has a more photon-starved geometry. The high temperature ($\sim$ 100 eV) of the soft-photon field entering and cooling it favors a localization of the hot corona in the inner flow. This soft-photon field could be part of the comptonised emission produced by the warm plasma. In this framework, the change in the geometry (i.e. $R_{tr}$) could explain most of the observed flux and spectral variability.Comment: 19 pages, 14 figures. Accepted for publication in A&