Symmetry and reciprocity constraints on diffraction by gratings of quasi-planar particles

Symmetry and reciprocity constraints on polarization state of the field diffracted by gratings of quasi-planar particles are considered. It is shown that the optical activity effects observed recently in arrays of quasi-planar plasmonic particles on a dielectric substrate are due to the reflection of the field at the air-dielectric slab interface and are proportional to this reflection coefficient.Comment: 11 pages, 3 figures, 12 references; minor corrections for better appearanc

Multi-wavelength study of XMMU J2235.3-2557: the most massive galaxy cluster at z > 1

[Abridged] XMMU J2235.3-2557 is one of the most distant X-ray selected clusters, spectroscopically confirmed at z=1.39. We characterize the galaxy populations of passive members, the thermodynamical properties of the hot gas, its metal abundance and the total mass of the system using imaging data with HST/ACS (i775 and z850 bands) and VLT/ISAAC (J and K_s bands), extensive spectroscopic data obtained with VLT/FORS2, and deep Chandra observations. Out of a total sample of 34 spectroscopically confirmed cluster members, we selected 16 passive galaxies within the central 2' (or 1 Mpc) with ACS coverage, and inferred star formation histories for a sub-sample of galaxies inside and outside the core by modeling their spectro-photometric data with spectral synthesis models, finding a strong mean age radial gradient. Chandra data show a regular elongated morphology, closely resembling the distribution of core galaxies, with a significant cool core. We measure a global X-ray temperature of kT=8.6(-1.2,+1.3) keV (68% c.l.). By detecting the rest-frame 6.7 keV Iron K line, we measure a metallicty Z= 0.26(+0.20,-0.16) Zsun. In the likely hypothesis of hydrostatic equilibrium, we obtain a total mass of Mtot(<1 Mpc)=(5.9+-1.3)10^14 Msun. Overall, our analysis implies that XMM2235 is the hottest and most massive bona-fide cluster discovered to date at z>1, with a baryonic content, both its galaxy population and intra-cluster gas, in a significantly advanced evolutionary stage at 1/3 of the current age of the Universe.Comment: 9 pages, 8 figures, accepted for publication in A&A (v2: typos/language style corrections, updated references

A Viewing Angle - Kinetic Luminosity Unification Scheme For BL Lacertae Objects

We propose a unified classification for BL Lac objects (BLs), focusing on the synchrotron peak frequency of the spectral energy distribution. The unification scheme is based on the angle Theta that describes the orientation of the relativistic jet and on the electron kinetic luminosity Lambda of the jet. We assume that Lambda scales with the size of the jet r in a self-similar fashion (Lambda propto r^2), as supported by observational data. The jets are self-similar in geometry and have the same pressure and median magnetic field at the inlet, independent of size. The self-similarity is broken for the highest energy electrons, which radiate mainly at high frequencies, since for large sources they suffer more severe radiative energy losses over a given fraction of the jet length. We calculate the optically thin synchrotron spectrum using an accelerating inner jet model based on simple relativistic gas dynamics and show that it can fit the observed infrared to X-ray spectrum of PKS 2155--304. We couple the accelerating jet model to the unification scheme and compare the results to complete samples of BLs. The negative apparent evolution of X-ray selected BLs is explained as a result of positive evolution of the jet electron kinetic luminosity $\Lambda_{kin}$. We review observational arguments in favor of the existence of scaled-down accretion disks and broad emission-line regions in BLs. The proposed unification scheme can explain the lack of observed broad emission lines in X-ray selected BLs, as well as the existence of those lines preferentially in luminous radio-selected BLs. Finally, we review observational arguments that suggest the extension of this unification scheme to all blazars.Comment: 32 pages, 8 figures, to be published in the ApJ (Oct 20, 1998

The isolated neutron star RBS1774 revisited. Revised XMM-Newton X-ray parameters and an optical counterpart from deep LBT-observations

We report optical B-band observations with the Large Binocular Telescope LBT of the isolated neutron star RBS1774. The stacked image with total exposure 2.5h reveals a candidate optical counterpart at mB = 26.96 +- 0.20 at position RA(2000) = 21:43:03.4, DEC(2000)} = +06:54:17:5, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and derive revised spectral and positional parameters. The predicted optical flux from the extrapolated X-ray spectrum is likely twice as high as reported before. The measured optical flux exceeds the extrapolated X-ray spectral flux by a factor ~40 (15 - 60 at 1sigma confidence). We interpret our detection and the spectral energy distribution as further evidence of a temperature structure over the neutron star's surface and present a pure thermal model reflecting both the SED and the pulsed fraction of the light curve.Comment: 7 pages, 7 figures, submitted to A&

The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies

We report on a large HST imaging survey of BL Lac objects, at spatial resolution ~10 times better than previous ground-based surveys. We focus on data reduction and analysis, describing the procedures used to model the host galaxy surface brightness radial profiles. A total of 69 host galaxies were resolved out of 110 objects observed, including almost all sources at z < 0.5. We classify them morphologically by fitting with either an exponential disk or a de~Vaucouleurs profile; when one fit is preferred over the other, in 58 of 69 cases, it is invariably the elliptical morphology. This is a very strong result given the large number of BL Lac objects, the unprecedented spatial resolution, and the homogeneity of the data set. With the present reclassification of the host galaxy of 1418+546 as an elliptical, there remain no undisputed examples of a disk galaxy hosting a BL Lac nucleus. This implies that, at 99% confidence, fewer than 7% of BL Lacs can be in disk galaxies. The apparent magnitude of the host galaxies varies with distance as expected if the absolute magnitudes are approximately the same, with a spread of +-1 mag, out to redshift z < 0.5. At larger redshifts, only 6 of 23 BL Lacs are resolved so the present data do not constrain possible luminosity evolution of the host galaxies. The collective Hubble diagram for BL Lac host galaxies and radio galaxies strongly supports their unification.Comment: Accepted for publication on ApJS. 43 pages. 10 figures. Figure 1 can also be downloaded from http://icarus.stsci.edu/~scarpa/tmp/hst_figure1.ta

The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue

Thanks to the large collecting area (3 x ~1500 cm$^2$ at 1.5 keV) and wide field of view (30' across in full field mode) of the X-ray cameras on board the European Space Agency X-ray observatory XMM-Newton, each individual pointing can result in the detection of hundreds of X-ray sources, most of which are newly discovered. Recently, many improvements in the XMM-Newton data reduction algorithms have been made. These include enhanced source characterisation and reduced spurious source detections, refined astrometric precision, greater net sensitivity and the extraction of spectra and time series for fainter sources, with better signal-to-noise. Further, almost 50\% more observations are in the public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science Centre (XMM-SSC) to produce a much larger and better quality X-ray source catalogue. The XMM-SSC has developed a pipeline to reduce the XMM-Newton data automatically and using improved calibration a new catalogue version has been produced from XMM-Newton data made public by 2013 Dec. 31 (13 years of data). Manual screening ensures the highest data quality. This catalogue is known as 3XMM. In the latest release, 3XMM-DR5, there are 565962 X-ray detections comprising 396910 unique X-ray sources. For the 133000 brightest sources, spectra and lightcurves are provided. For all detections, the positions on the sky, a measure of the quality of the detection, and an evaluation of the X-ray variability is provided, along with the fluxes and count rates in 7 X-ray energy bands, the total 0.2-12 keV band counts, and four hardness ratios. To identify the detections, a cross correlation with 228 catalogues is also provided for each X-ray detection. 3XMM-DR5 is the largest X-ray source catalogue ever produced. Thanks to the large array of data products, it is an excellent resource in which to find new and extreme objects.Comment: 23 pages, version accepted for publication in A&

X-ray Spectral Survey with XMM--Newton of a Complete Sample of Nearby Seyfert Galaxies

Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM--Newton are reported. The sample was optically selected, well defined, complete in B mag, and distance limited: it consists of the nearest (D<22 Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997) sample. This is one of the largest atlases of hard X-ray spectra of low-L active galaxies ever assembled. All nuclear sources except two Sey 2s are detected between 2-10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 10**38 erg/s. The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects (> 30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Sey, as expected from ``unified models'', (ii) Sey galaxies as a whole are distributed fairly continuously over the entire range of Nh, between 10**20 and 10**25 cm**-2, and (iii) while Sey 1s tend to have lower Nh and Sey 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample well represents the average intrinsic X-ray spectral properties of nearby AGN, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Sey galaxies, and extends their validity down to very low luminosities.Comment: 23 pages, 4 tables, 4 figures, 2 Appendices with 27 source spectra and notes, to be published in the Astronomy & Astrophysics Journa

Correlated intense X-ray and TeV activity of Mrk~501 in 1998 June

We present exactly simultaneous X-ray and TeV monitoring with {\it RXTE} and HEGRA of the TeV blazar Mrk 501 during 15 days in 1998 June. After an initial period of very low flux at both wavelengths, the source underwent a remarkable flare in the TeV and X-ray energy bands, lasting for about six days and with a larger amplitude at TeV energies than in the X-ray band. At the peak of the TeV flare, rapid TeV flux variability on sub-hour timescales is found. Large spectral variations are observed at X-rays, with the 3--20 keV photon index of a pure power law continuum flattening from $\Gamma=2.3$ to $\Gamma=1.8$ on a timescale of 2--3 days. This implies that during the maximum of the TeV activity, the synchrotron peak shifted to energies $\gtrsim 50$ keV, a behavior similar to that observed during the longer-lasting, more intense flare in 1997 April. The TeV spectrum during the flare is described by a power law with photon index $\Gamma=1.9$ and an exponential cutoff at $\sim$ 4 TeV; an indication for spectral softening during the flare decay is observed in the TeV hardness ratios. Our results generally support a scenario where the TeV photons are emitted via inverse Compton scattering of ambient seed photons by the same electron population responsible for the synchrotron X-rays. The simultaneous spectral energy distributions (SEDs) can be fit with a one-zone synchrotron-self Compton model assuming a substantial increase of the magnetic field and the electron energy by a factor of 3 and 10, respectively.Comment: Accepted for publication in ApJ, Part

The Hot and Energetic Universe: The evolution of galaxy groups and clusters

Major astrophysical questions related to the formation and evolution of structures, and more specifically of galaxy groups and clusters, will still be open in the coming decade and beyond: what is the interplay of galaxy, supermassive black hole, and intergalactic gas evolution in the most massive objects in the Universe - galaxy groups and clusters? What are the processes driving the evolution of chemical enrichment of the hot diffuse gas in large-scale structures? How and when did the first galaxy groups in the Universe, massive enough to bind more than 10^7 K gas, form? Focussing on the period when groups and clusters assembled (0.5<z<2.5), we show that, due to the continuum and line emission of this hot intergalactic gas at X-ray wavelengths, Athena+, combining high sensitivity with excellent spectral and spatial resolution, will deliver breakthrough observations in view of the aforementioned issues. Indeed, the physical and chemical properties of the hot intra-cluster gas, and their evolution across time, are a key to understand the co-evolution of galaxy and supermassive black hole within their environments.Comment: Supporting paper for the science theme The Hot and Energetic Universe to be implemented by the Athena+ X-ray observatory (http://www.the-athena-x-ray-observatory.eu). 10 pages, 4 figure

The eROSITA X-ray telescope on SRG

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2-2.3 keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3-8 keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts z &gt; 1 in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements