Gaia broad band photometry

The scientific community needs to be prepared to analyse the data from Gaia, one of the most ambitious ESA space missions, to be launched in 2012. The purpose of this paper is to provide data and tools in order to predict in advance how Gaia photometry is expected to be. To do so, we provide relationships among colours involving Gaia magnitudes and colours from other commonly used photometric systems (Johnson-Cousins, SDSS, Hipparcos and Tycho). The most up-to-date information from industrial partners has been used to define the nominal passbands and based on the BaSeL3.1 stellar spectral energy distribution library, relationships were obtained for stars with different reddening values, ranges of temperatures, surface gravities and metallicities. The transformations involving Gaia and Johnson-Cousins V-I_C and Sloan DSS g-z colours have the lowest residuals. A polynomial expression for the relation between the effective temperature and the colour G_BP-G_RP was derived for stars with T > 4500 K. Transformations involving two Johnson or two Sloan DSS colours yield lower residuals than using only one colour. We also computed several ratios of total-to-selective absorption including absorption A_G in the G band and colour excess E(G_BP-G_RP) for our sample stars. A relationship, involving A_G/A_V and the intrinsic (V-I_C) colour, is provided. The derived Gaia passbands have been used to compute tracks and isochrones using the Padova and BASTI models. Finally, the performances of the predicted Gaia magnitudes have been estimated according to the magnitude and the celestial coordinates of the star. The provided dependencies among colours can be used for planning scientific exploitation of Gaia data, performing simulations of the Gaia-like sky, planning ground-based complementary observations and for building catalogues with auxiliary data for the Gaia data processing and validation.Comment: 15 pages and 19 figure (accepted in A&A

Lightweight, broad-band spectrum analyzer

Spectrum analyzer, utilizing techniques similar to those used to classify energy levels of nuclear particles, is incorporated into electric field detector. Primary advantage is ability to perform qualitative broad-band frequency analysis over a large dynamic amplitude range with minimum weight and electrical power requirements

Broad Band Equilibration of Strangeness

We develop the "broad band equilibration" scenario for kaon productions at GSI energies with in-medium effects.Comment: 4 pages, latex with 2 eps figure, a talk in QM200

Broad-Band Soft X-ray Polarimetry

We developed an instrument design capable of measuring linear X-ray polarization over a broad-band using conventional spectroscopic optics. A set of multilayer-coated flats reflects the dispersed X-rays to the instrument detectors. The intensity variation with position angle is measured to determine three Stokes parameters: I, Q, and U -- all as a function of energy. By laterally grading the multilayer optics and matching the dispersion of the gratings, one may take advantage of high multilayer reflectivities and achieve modulation factors > 50% over the entire 0.2 to 0.8 keV band. This instrument could be used in a small orbiting mission or scaled up for the International X-ray Observatory. Laboratory work has begun that would demonstrate the capabilities of key components.Comment: 6 pages, 3 figures (2 color); to appear in proceedings of "The Coming of Age of X-ray Polarimetry

Broad-band Modeling of GRB Afterglows

Observations of GRB afterglows ranging from radio to X-ray frequencies generate large data sets. Careful analysis of these broad-band data can give us insight into the nature of the GRB progenitor population by yielding such information like the total energy of the burst, the geometry of the fireball and the type of environment into which the GRB explodes. We illustrate, by example, how global, self-consistent fits are a robust approach for characterizing the afterglow emission. This approach allows a relatively simple comparison of different models and a way to determine the strengths and weaknesses of these models, since all are treated self-consistently. Here we quantify the main differences between the broad-band, self-consistent approach and the traditional approach, using GRB000301C and GRB970508 as test cases.Comment: Appears in "Gamma-Ray Bursts in the Afterglow Era" proceedings of the Roma 2000 GRB Workshop; 3 pages; 2 figure

Broad-band variability in accreting compact objects

Cataclysmic variable stars are in many ways similar to X-ray binaries. Both types of systems possess an accretion disk, which in most cases can reach the surface (or event horizon) of the central compact object. The main difference is that the embedded gravitational potential well in X-ray binaries is much deeper than those found in cataclysmic variables. As a result, X-ray binaries emit most of their radiation at X-ray wavelengths, as opposed to cataclysmic variables which emit mostly at optical/ultraviolet wavelengths. Both types of systems display aperiodic broad-band variability which can be associated to the accretion disk. Here, the properties of the observed X-ray variability in XRBs are compared to those observed at optical wavelengths in CVs. In most cases the variability properties of both types of systems are qualitatively similar once the relevant timescales associated with the inner accretion disk regions have been taken into account. The similarities include the observed power spectral density shapes, the rms-flux relation as well as Fourier-dependant time lags. Here a brief overview on these similarities is given, placing them in the context of the fluctuating accretion disk model which seeks to reproduce the observed variability.Comment: Invited talk and accepted for publication in Acta Polytechnica, Proceedings of "The Golden Age of Cataclysmic Variables and Related Objects II

Design of broad-band PMD compensation filters

We describe a new design approach for broad-band polarization-mode dispersion (PMD) compensation filters. An efficient algorithm for minimization of the maximum differential group delay within a given frequency band is described

Bandpass Dependence of X-ray Temperatures in Galaxy Clusters

We explore the band dependence of the inferred X-ray temperature of the intracluster medium (ICM) for 192 well-observed galaxy clusters selected from the Chandra Data Archive. If the hot ICM is nearly isothermal in the projected region of interest, the X-ray temperature inferred from a broad-band (0.7-7.0 keV) spectrum should be identical to the X-ray temperature inferred from a hard-band (2.0-7.0 keV) spectrum. However, if unresolved cool lumps of gas are contributing soft X-ray emission, the temperature of a best-fit single-component thermal model will be cooler for the broad-band spectrum than for the hard-band spectrum. Using this difference as a diagnostic, the ratio of best-fitting hard-band and broad-band temperatures may indicate the presence of cooler gas even when the X-ray spectrum itself may not have sufficient signal-to-noise to resolve multiple temperature components. To test this possible diagnostic, we extract X-ray spectra from core-excised annular regions for each cluster in our archival sample. We compare the X-ray temperatures inferred from single-temperature fits when the energy range of the fit is 0.7-7.0 keV (broad) and when the energy range is 2.0/(1+z)-7.0 keV (hard). We find that the hard-band temperature is significantly higher, on average, than the broad-band temperature. Upon further exploration, we find this temperature ratio is enhanced preferentially for clusters which are known merging systems. In addition, cool-core clusters tend to have best-fit hard-band temperatures that are in closer agreement with their best-fit broad-band temperatures. We show, using simulated spectra, that this diagnostic is sensitive to secondary cool components (TX = 0.5-3.0 keV) with emission measures >10-30% of the primary hot component.Comment: Accepted for publication in Ap