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Villanueva de la Cañada, Spain

Diaz Trigo M.,ESO | Sidoli L.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Boirin L.,11 Rue Of Luniversite | Parmar A.N.,ESAC
Astronomy and Astrophysics | Year: 2012

We analysed data from five XMM-Newton observations of GX 13 + 1 to investigate the variability of the photo-ionised absorber in this source. We fitted EPIC and RGS spectra obtained from the "least-variable" intervals with a model consisting of disc-blackbody and blackbody components together with a Gaussian emission feature at ∼6.55-6.7 keV modified by absorption due to cold and photo-ionised material. We found a significant correlation between the hard, ∼6-10 keV, flux, the ionisation and column density of the absorber and the equivalent width of the broad iron line. We interpret the correlation in a scenario in which a disc wind is thermally driven at large, ∼1010 cm, radii and the broad line results from reprocessed emission in the wind and/or hot atmosphere. The breadth of the emission line is naturally explained by a combination of scattering, recombination and fluorescence processes. We attribute the variations in the absorption and emission along the orbital period to the view of different parts of the wind, possibly located at slightly different inclination angles. We constrain the inclination of GX 13 + 1 to be between 60 and 80° from the strong absorption in the line of sight, which obscures up to 80% of the total emission in one observation, and the absence of eclipses. We conclude that either a disc wind and/or a hot atmosphere can explain the current observations of narrow absorption and broad iron emission features in neutron star low-mass X-ray binaries as a class. © 2012 ESO. Source

Rahoui F.,Harvard University | Rahoui F.,Harvard Smithonian Center for Astrophysics | Coriat M.,University of Southampton | Corbel S.,University Paris Diderot | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

The microquasar GX 339-4, known to exhibit powerful compact jets that dominate its radio to near-infrared emission, entered an outburst in 2010 for the fifth time in about 15yr. An extensive radio to X-ray multiwavelength campaign was immediately triggered, and we report here on European Southern Observatory/FORS2+ISAAC optical and near-infrared spectroscopic observations, supported by Australia Telescope Compact Array radio and Rossi X-ray Timing Experiment/Swift X-ray quasi-simultaneous data. GX 339-4 was observed at three different epochs, once in the soft state and twice in the hard state. In the soft state, the optical and near-infrared continuum is largely consistent with the Raleigh-Jeans tail of a thermal process. As an explanation, we favour irradiation of the outer accretion disc by its inner regions, enhanced by disc warping. An excess is also present at low frequencies, likely due to an M subgiant companion star. During the first hard state, the optical/near-infrared continuum is well described by the optically thin synchrotron emission of the compact jet combined with disc irradiation and perhaps another component peaking in the ultraviolet. The spectral break where the jet transits from the optically thick to thin regimes, located below 1.20 × 10 14Hz, is not detected and the extension of the optically thin synchrotron is consistent with the 3-50keV spectrum. In contrast, the emission during the second hard state is more difficult to understand and points towards a more complex jet continuum. In both cases, the near-infrared continuum is found to be variable at time-scales at least as short as 20s, although these variabilities are smoothed out beyond a few hundred seconds. This implies rapid variations - in flux and frequency - of the location of the spectral break, i.e. dramatic short time-scale changes of the physical conditions at the base of the jet, such as the magnetic field and/or the base radius. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source

Sklias P.,Observatoire de Geneva | Zamojski M.,Observatoire de Geneva | Schaerer D.,Observatoire de Geneva | Schaerer D.,French National Center for Scientific Research | And 11 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Multi-wavelength, optical to IR/submm observations of strongly lensed galaxies identified by the Herschel Lensing Survey are used to determine the physical properties of high-redshift star-forming galaxies close to or below the detection limits of blank fields. Aims. We aim to constrain theIR stellar and dust content, and to determine star formation rates and histories, dust attenuation and extinction laws, and other related properties. Methods. We studied a sample of seven galaxies with spectroscopic redshifts z ∼ 1.5-3 that have been detected with precision thanks to gravitational lensing, and whose spectral energy distribution (SED) has been determined from the rest-frame UV to the IR/mm domain. For comparison, our sample includes two previously well-studied lensed galaxies, MS1512-cB58 and the Cosmic Eye, for which we also provide updated Herschel measurements. We performed SED fits of the full photometry of each object, and of the optical and infrared parts separately, exploring various star formation histories, using different extinction laws, and exploring the effects of nebular emission. The IR luminosity, in particular, is predicted consistently from the stellar population model. The IR observations and emission line measurements, where available, are used as a posteriori constraints on the models. We also explored energy conserving models, that we created by using the observed IR/UV ratio to estimate the extinction. Results. Among the models we have tested, models with exponentially declining star-forming histories including nebular emission and assuming the Calzetti attenuation law best fit most of the observables. Models assuming constant or rising star formation histories predict in most cases too much IR luminosity. The SMC extinction law underpredicts the IR luminosity in most cases, except for two out of seven galaxies, where we cannot distinguish between different extinction laws. Our sample has a median lensing-corrected IR luminosity ∼3 × 1011Lr, stellar masses between 2 × 10 9Mr and 2 × 1011Me, and IR/UV luminosity ratios spanning a wide range. The dust masses of our galaxies are in the range [2-17] × 107Mt, extending previous studies at the same redshift down to lower masses. We do not find any particular trend of the dust temperature Tdust with LIR, suggesting an overall warmer dust regime at our redshift regardless of IR luminosity. Conclusions. Gravitational lensing enables us to study the detailed physical properties of individual IR-detected z ∼ 1.5-3 galaxies up to a factor of ∼10 fainter than achieved with deep blank field observations. We have in particular demonstrated that multi-wavelength observations combining stellar and dust emission can constrain star formation histories and extinction laws of star-forming galaxies, as proposed in an earlier paper. Fixing the extinction based on the IR/UV observations successfully breaks the age-extinction degeneracy often encountered in obscured galaxies. © ESO, 2014. Source

Weisskopf M.C.,NASA | Guainazzi M.,ESAC | Jahoda K.,NASA | Shaposhnikov N.,College Park | And 4 more authors.
Astrophysical Journal | Year: 2010

Motivated by a paper of Kirsch et al. on possible use of the Crab Nebula as a standard candle for calibrating X-ray response functions, we examine consequences of intrinsic departures from a single (absorbed) power law upon such calibrations. We limit our analyses to three more modern X-ray instruments - the ROSAT/PSPC, the RXTE/Proportional Counter Array, and the XMM-Newton/EPIC-pn (burst mode). The results indicate a need to refine two of the three response functions studied. We are also able to distinguish between two current theoretical models for the system spectrum. © 2010 The American Astronomical Society. Source

Rawle T.D.,ESAC | Lucey J.R.,Durham University | Smith R.J.,Durham University | Head J.T.C.G.,Durham University
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present deep Gemini Multi-Object Spectrograph long-slit spectroscopy of 15 Coma cluster SO galaxies, and extract kinematic properties along the major axis to several times the disc scalelength. Supplementing our data set with previously published data, we create a combined sample of 29 Coma SOs, as well as a comparison sample of 38 Coma spirals. Using photometry from the Sloan Digital Sky Survey and Two Micron All Sky Survey, we construct the Tully-Fisher relation (TFR; luminosity versus maximum rotational velocity) for SO galaxies. At fixed rotational velocity, the Coma SO galaxies are on average fainter than Coma spirals by 1.10 ± 0.18, 0.86 ±0.19 and 0.83 ± 0.19 mag in the g, i and KS bands, respectively. The typical SO offsets remain unchanged when calculated relative to large field-galaxy spiral samples. The observed offsets are consistent with a simple star formation model in which S0s are identical to spirals until abrupt quenching occurs at some intermediate redshift. The offsets form a continuous distribution tracing the time since the cessation of star formation, and exhibit a strong correlation (>6σ) with residuals from the optical colour-magnitude relation. Typically. SOs which are fainter than average for their rotational velocity are also redder than average for their luminosity. The SO TFR offset is also correlated with both the projected cluster-centric radius and the Σ (projected) local density parameter. Since current local environment is correlated with time of accretion into the cluster, our results support a scenario in which transformation of spirals to SOs is triggered by cluster infall.© 2013 The Authors. Source

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