Observations of Cygnus X-1 in the MeV band by the INTEGRAL imager

The spectrum of the MeV tail detected in the black-hole candidate Cygnus X-1 remains controversial as it appeared much harder when observed with the INTEGRAL Imager IBIS than with the INTEGRAL spectrometer SPI or CGRO. We present an independent analysis of the spectra of Cygnus X-1 observed by IBIS in the hard and soft states. We developed a new analysis software for the PICsIT detector layer and for the Compton mode data of the IBIS instrument and calibrated the idiosyncrasies of the PICsIT front-end electronics. The spectra of Cygnus X-1 obtained for the hard and soft states with the INTEGRAL imager IBIS are compatible with those obtained with the INTEGRAL spectrometer SPI, with CGRO, and with the models that attribute the MeV hard tail either to hybrid thermal/non-thermal Comptonisation or to synchrotron emission.Comment: 6 pages, 7 figure

Fossil life on Mars

Three major problems beset paleontologists searching for morphological evidence of life on early Earth: selecting a prospective site; finding biogenic structures; and distinguishing biogenic from abiogenic structures. The same problems arise on Mars. Terrestrial experience suggests that, with the techniques that can be employed remotely, ancient springs, including hot springs, are more prospective than lake deposits. If, on the other hand, the search is for chemical evidence, the strategy can be very different, and lake deposits are attractive targets. Lakes and springs frequenly occur in close proximity, and therefore a strategy that combines the two would seem to maximize the chance of success. The strategy for a search for stromatolite on Mars is discussed

Neutron star masses from hydrodynamical effects in obscured sgHMXBs

A population of obscured supergiant High Mass X-ray Binaries (sgHMXBs) has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration. The main goal of this study is to understand under which conditions high obscuration could occur. We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters. We have constrained the wind terminal velocity to 500-600 km/s and the neutron star mass to 1.75-2.15 solar masses. We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.Comment: A&A in pres

The X-ray Spectrum of the z=6.30 QSO SDSS J1030+0524

We present a deep XMM-Newton observation of the z=6.30 QSO SDSS J1030+0524, the second most distant quasar currently known. The data contain sufficient counts for spectral analysis, demonstrating the ability of XMM-Newton to measure X-ray spectral shapes of z~6 QSOs with integration times >100ks. The X-ray spectrum is well fit by a power law with index Gamma=2.12 +/- 0.11, an optical-X-ray spectral slope of a_{ox}=-1.80, and no absorption excess to the Galactic value, though our data are also consistent with a power law index in the range 2.02 < Gamma < 2.5 and excess absorption in the range 0 < N_H(cm^-2) < 8x10^22. There is also a possible detection (2 sigma) of FeKa emission. The X-ray properties of this QSO are, overall, similar to those of lower-redshift radio-quiet QSOs. This is consistent with the statement that the X-ray properties of radio-quiet QSOs show no evolution over 0<z<6.3. Combined with previous results, this QSO appears indistinguishable in any way from lower redshift QSOs, indicating that QSOs comparable to those seen locally existed less than one Gyr after the Big Bang.Comment: ApJ Letters, accepte

Relationship between X-ray and ultraviolet emission in 3C 273

In 3C 273, ultraviolet flux and X-ray flux measured by BATSE are not well correlated, contrarily to predictions of several models, unless the X-ray flux lags the UV emission by 1.75 yr. The absence of observed correlation at small lag cannot be due to spectral variability. A Comptonizing corona model is however compatible with all UV and X-ray observations covering the BATSE period.Comment: LaTeX, 4 pages, 6 figures. espcrc2.sty style file included. Poster contribution to the symposium "The Active X-ray Sky: Results from BepppoSAX and Rossi-XTE", Rome, October 199

CP Violating Asymmetry in Stop Decay into Bottom and Chargino

In the MSSM with complex parameters, loop corrections to the decay of a stop into a bottom quark and a chargino can lead to a CP violating decay rate asymmetry. We calculate this asymmetry at full one-loop level and perform a detailed numerical study, analyzing the dependence on the parameters and complex phases involved. In addition, we take the Yukawa couplings of the top and bottom quark running. We account for the constraints on the parameters coming from several experimental limits. Asymmetries of several percent are obtained. We also comment on the feasibility of measuring this asymmetry at the LHC.Comment: Contributed talk given by Sebastian Frank in June 2009 at SUSY09 - 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions, Northeastern University, Boston, USA. To appear in the AIP conference proceedings, 4 pages, 7 figures (fixed links in references

Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre

The Galactic centre is a bright gamma-ray source with the GeV-TeV band spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV energy ranges. The nature of these two components is not clearly understood. We investigate the gamma-ray properties of the Galactic centre to clarify the origin of the observed emission. We report imaging, spectral, and timing analysis of data from 74 months of observations of the Galactic centre by FERMI/LAT gamma-ray telescope complemented by sub-MeV data from approximately ten years of INTEGRAL/PICsIT observations. We find that the Galactic centre is spatially consistent with the point source in the GeV band. The tightest 3 sigma upper limit on its radius is 0.13 degree in the 10-300 GeV energy band. The spectrum of the source in the 100 MeV energy range does not have a characteristic turnover that would point to the pion decay origin of the signal. Instead, the source spectrum is consistent with a model of inverse Compton scattering by high-energy electrons. In this a model, the GeV bump in the spectrum originates from an episode of injection of high-energy particles, which happened ~300 years ago. This injection episode coincides with the known activity episode of the Galactic centre region, previously identified using X-ray observations. The hadronic model of source activity could be still compatible with the data if bremsstrahlung emission from high-energy electrons was present in addition to pion decay emission.Comment: To match the accepted versio

Evaluation of directionally solidified eutectic superalloys for turbine blade applications

Alloys from the following systems were selected for property evaluation: (1) gamma/gamma-Mo (Ni-base, rods of Mo); (2) gamma-beta (Ni-base, lamellae or rods of (Ni, Fe/Co Al); and (3) gamma-gamma (Ni-base rods of Ni3Al gamma). The three alloys were subjected to longitudinal and transverse tensile and rupture tests from 750 C to 1100 C, longitudinal shear strength was measured at several temperatures, resistance to thermal cycling to 1150 C was determined, cyclic oxidation resistance was evaluated at 750 C and 1100 C, and each system was directionally solidified in an alumina shell mold turbine shape to evaluate mold/metal reactivity. The gamma/gamma Mo system has good rupture resistance, transverse properties and processability, and is a high potential system for turbine blades. The gamma-beta system has good physical properties and oxidation resistance, and is a potential system for turbine vanes. The gamma-gamma system has good high temperature rupture resistance and requires further exploratory research