High-energy Astrophysics and the Virtual Observatory

The Virtual Observatory (VO) will revolutionise the way we do Astronomy by allowing easy access to all astronomical data and by making the handling and analysis of datasets at various locations across the globe much simpler and faster. I report here on the need for the VO and its status in Europe, concentrating on the recently started EURO-VO project, and then give two specific applications of VO tools to high-energy astrophysics.Comment: 12 pages, 3 figures, invited talk at the Workshop ``Multifrequency Behaviour of High Energy Cosmic Sources'', Vulcano, Italy, May 2005, F. Giovannelli et al., in pres

NEOWISE observations of comet C/2013 A1 (Siding Spring) as it approaches Mars

The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission observed comet C/2013 A1 (Siding Spring) three times at 3.4 {\mu}m and 4.6 {\mu}m as the comet approached Mars in 2014. The comet is an extremely interesting target since its close approach to Mars in late 2014 will be observed by various spacecraft in-situ. The observations were taken in 2014 Jan., Jul. and Sep. when the comet was at heliocentric distances of 3.82 AU, 1.88 AU, and 1.48 AU. The level of activity increased significantly between the Jan. and Jul. visits but then decreased by the time of the observations in Sep., approximately 4 weeks prior to its close approach to Mars. In this work we calculate Af\r{ho} values, and CO/CO2 production rates.Comment: 9 pages, 3 figures, accepted by Astrophysical Journal Letter

The WISE AGN Catalog

We present two large catalogs of AGN candidates identified across ~75% of the sky from the Wide-field Infrared Survey Explorer's AllWISE Data Release. Both catalogs, some of the largest such catalogs published to date, are selected purely on the basis of mid-IR photometry in the WISE W1 and W2 bands. The catalogs are designed to be appropriate for a broad range of scientific investigations, with one catalog emphasizing reliability while the other emphasizes completeness. Specifically, the R90 catalog consists of 4,543,530 AGN candidates with 90% reliability, while the C75 catalog consists of 20,907,127 AGN candidates with 75% completeness. We provide a detailed discussion of potential artifacts, and excise portions of the sky close to the Galactic Center, Galactic Plane, nearby galaxies, and other expected contaminating sources. Our final catalogs cover 30,093 deg^2 of extragalactic sky. These catalogs are expected to enable a broad range of science, and we present a few simple illustrative cases. From the R90 sample we identify 45 highly variable AGN lacking radio counterparts in the FIRST survey, implying they are unlikely to be blazars. One of these sources, WISEA J142846.71+172353.1, is a mid-IR-identified changing-look quasar at z=0.104. We characterize our catalogs by comparing them to large, wide-area AGN catalogs in the literature, specifically UV-to-near-IR quasar selections from SDSS and XDQSOz, mid-IR selection from Secrest et al. (2015) and X-ray selection from ROSAT. From the latter work, we identify four ROSAT X-ray sources that each are matched to three WISE-selected AGN in the R90 sample within 30". Palomar spectroscopy reveals one of these systems, 2RXS J150158.6+691029, to consist of a triplet of quasars at z=1.133 +/- 0.004, suggestive of a rich group or forming galaxy cluster.(Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplements. Updated with comments from the referee. 20 pages, 15 figures, 8 tables. The WISE AGN Catalogs can be made available upon request by writing to [email protected]

Thermal Model Calibration for Minor Planets Observed with Wide-Field Infrared Survey Explorer/Neowise

With the Wide-field Infrared Survey Explorer (WISE), we have observed over 157,000 minor planets. Included in these are a number of near-Earth objects, main-belt asteroids, and irregular satellites which have well measured physical properties (via radar studies and in situ imaging) such as diameters. We have used these objects to validate models of thermal emission and reflected sunlight using the WISE measurements, as well as the color corrections derived in Wright et al. for the four WISE bandpasses as a function of effective temperature. We have used 50 objects with diameters measured by radar or in situ imaging to characterize the systematic errors implicit in using the WISE data with a faceted spherical near-Earth asteroid thermal model (NEATM) to compute diameters and albedos. By using the previously measured diameters and H magnitudes with a spherical NEATM model, we compute the predicted fluxes (after applying the color corrections given in Wright et al.) in each of the four WISE bands and compare them to the measured magnitudes. We find minimum systematic flux errors of 5%-10%, and hence minimum relative diameter and albedo errors of ~10% and ~20%, respectively. Additionally, visible albedos for the objects are computed and compared to the albedos at 3.4 μm and 4.6 μm, which contain a combination of reflected sunlight and thermal emission for most minor planets observed by WISE. Finally, we derive a linear relationship between subsolar temperature and effective temperature, which allows the color corrections given in Wright et al. to be used for minor planets by computing only subsolar temperature instead of a faceted thermophysical model. The thermal models derived in this paper are not intended to supplant previous measurements made using radar or spacecraft imaging; rather, we have used them to characterize the errors that should be expected when computing diameters and albedos of minor planets observed by WISE using a spherical NEATM model

NEOWISE: Observations of the Irregular Satellites of Jupiter and Saturn

We present thermal model fits for 11 Jovian and 3 Saturnian irregular satellites based on measurements from the WISE/NEOWISE dataset. Our fits confirm spacecraft-measured diameters for the objects with in situ observations (Himalia and Phoebe) and provide diameters and albedo for 12 previously unmeasured objects, 10 Jovian and 2 Saturnian irregular satellites. The best-fit thermal model beaming parameters are comparable to what is observed for other small bodies in the outer Solar System, while the visible, W1, and W2 albedos trace the taxonomic classifications previously established in the literature. Reflectance properties for the irregular satellites measured are similar to the Jovian Trojan and Hilda Populations, implying common origins.Comment: 17 pages, 3 figures, accepted for publication in Astrophysical Journa

X-ray emission from the field of the hyperluminous IRAS galaxy IRASF15307+3252

We report on a 20-ks observation of the z = 0.93 hyperluminous galaxy IRAS F15307+3252 with the ROSAT HRI. No X-ray source is detected at the position of F15307+3252 at an upper limit of ∼4 × 10⁴³ erg s⁻¹. This is less than 2 × 10⁻⁴ of the bolometric luminosity of the object, and indicates either that the nucleus emits an unusually small fraction of its total power in X-rays, or that little of the nuclear X-ray flux is scattered into our line of sight by electrons. The lack of an X-ray detection around F15307+3252 also rules out it being at the centre of a cluster, such as is observed for IRAS P09104+4109. A weak, possibly extended, X-ray source is detected 13 arcsec south of the galaxy, spatially coincident with a clump of faint objects visible in a Keck K_s-band image of the field. This may be the core of a cluster near the line of sight to F15307+3252

Structure Function Scaling of a 2MASS Extinction Map of Taurus

We compute the structure function scaling of a 2MASS extinction map of the Taurus molecular cloud complex. The scaling exponents of the structure functions of the extinction map follow the Boldyrev's velocity structure function scaling of supersonic turbulence. This confirms our previous result based on a spectral map of 13CO J=1-0 covering the same region and suggests that supersonic turbulence is important in the fragmentation of this star--forming cloud.Comment: submitted to Ap