Ambitious STS-7 mission to feature first landing at Kennedy

The STS-7 press briefing schedule, NASA select television schedule; launch preparations, countdown and liftoff; major countdown milestones; launch window; STS-7 flight sequence of events, landing timeline; STS-7 flight timeline; landing and post landing operations; flight objectives; Telesat's ANIK-C 2; PALAPA-B; STS-7 experiments; and spacecraft tracking and data network are presented

Is an obscured AGN at the centre of the disk galaxy IC 2497 responsible for Hanny's Voorwerp?

We present the results of VLBI and MERLIN observations of the massive disk galaxy IC 2497. Optical observations of IC 2497 revealed the existence of a giant emission nebula "Hanny's Voorwerp" in the proximity of the galaxy. Earlier short-track 18 cm observations with e-VLBI at 18 cm, detected a compact radio component (C1) at the centre of IC 2497. The brightness temperature of C1 was measured to be greater than 4E5 K. Deeper, long-track e-VLBI observations presented here, re-confirm the existence of C1 but also reveal the existence of a second compact component (C2) located about 230 milliarcseconds to the North-East of C1. The brightness temperature of C2 is measured to be greater than 1.4E5 K, suggesting that both components may be related to AGN activity (e.g. a radio core and jet hotspot). Lower resolution 18cm MERLIN observations show both components. C1 is shown to be compact with a slight elongation along the direction of Hanny's Voorwerp, and C2 shows a lot of extended emission in an almost perpendicular direction to the direction of the Voorwerp. Our results continue to support the hypothesis that IC 2497 contains an Active Galactic Nucleus (AGN), and that a jet associated with this AGN clears a path that permits ionising radiation from the AGN to directly illuminate the emission nebula.Comment: Presented at The 8th International e-VLBI Workshop: the Science and Technology of Long Baseline Real-Time Interferometry, EXPReS09, June 22-26 2009 Madrid, Spain. 5 pages, 5 article

WSRT 1.4 GHz Observations of the Hubble Deep Field

We present WSRT 1.38 GHz observations of the Hubble Deep Field (and flanking fields). 72 hours of data were combined to produce the WSRT's deepest image yet, achieving an r.m.s. noise level of 8 microJy per beam. We detect radio emission from galaxies both in the HDF and HFF which have not been previously detected by recent MERLIN or VLA studies of the field.Comment: 2 pages, 1 figure, to appear in "The Universe at Low Radio Frequencies", IAU Symposium 199. For colour figures, see http://www.nfra.nl/~mag/hdf_wsrt.htm

Magnification Ratio of the Fluctuating Light in Gravitational Lens 0957+561

Radio observations establish the B/A magnification ratio of gravitational lens 0957+561 at about 0.75. Yet, for more than 15 years, the optical magnfication ratio has been between 0.9 and 1.12. The accepted explanation is microlensing of the optical source. However, this explanation is mildly discordant with (i) the relative constancy of the optical ratio, and (ii) recent data indicating possible non-achromaticity in the ratio. To study these issues, we develop a statistical formalism for separately measuring, in a unified manner, the magnification ratio of the fluctuating and constant parts of the light curve. Applying the formalism to the published data of Kundi\'c et al. (1997), we find that the magnification ratios of fluctuating parts in both the g and r colors agrees with the magnification ratio of the constant part in g-band, and tends to disagree with the r-band value. One explanation could be about 0.1 mag of consistently unsubtracted r light from the lensing galaxy G1, which seems unlikely. Another could be that 0957+561 is approaching a caustic in the microlensing pattern.Comment: 12 pages including 1 PostScript figur

Values of H_0 from Models of the Gravitational Lens 0957+561

The lensed double QSO 0957+561 has a well-measured time delay and hence is useful for a global determination of H0. Uncertainty in the mass distribution of the lens is the largest source of uncertainty in the derived H0. We investigate the range of \hn produced by a set of lens models intended to mimic the full range of astrophysically plausible mass distributions, using as constraints the numerous multiply-imaged sources which have been detected. We obtain the first adequate fit to all the observations, but only if we include effects from the galaxy cluster beyond a constant local magnification and shear. Both the lens galaxy and the surrounding cluster must depart from circular symmetry as well. Lens models which are consistent with observations to 95% CL indicate H0=104^{+31}_{-23}(1-\kthirty) km/s/Mpc. Previous weak lensing measurements constrain the mean mass density within 30" of G1 to be kthirty=0.26+/-0.16 (95% CL), implying H0=77^{+29}_{-24}km/s/Mpc (95% CL). The best-fitting models span the range 65--80 km/s/Mpc. Further observations will shrink the confidence interval for both the mass model and \kthirty. The range of H0 allowed by the full gamut of our lens models is substantially larger than that implied by limiting consideration to simple power law density profiles. We therefore caution against use of simple isothermal or power-law mass models in the derivation of H0 from other time-delay systems. High-S/N imaging of multiple or extended lensed features will greatly reduce the H0 uncertainties when fitting complex models to time-delay lenses.Comment: AASTEX, 48 pages 4 figures, 2 tables. Also available at: http://www.astro.lsa.umich.edu:80/users/philf/www/papers/list.htm

High-z radio starbursts host obscured X-ray AGN

We use Virtual Observatory methods to investigate the association between radio and X-ray emission at high redshifts. Fifty-five of the 92 HDF(N) sources resolved by combining MERLIN+VLA data were detected by Chandra, of which 18 are hard enough and bright enough to be obscured AGN. The high-z population of microJy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at z<1 and at least a quarter of these simultaneously host highly X-ray-luminous obscured AGN.Comment: 4 pages, 2 figures, To appear in the proceedings of 'At the Edge of the Universe' (9-13 October 2006, Sintra, Portugal

Hybridization gap versus hidden order gap in URu2_2Si2_2 as revealed by optical spectroscopy

We present the in-plane optical reflectance measurement on single crystals of URu$_2$As$_2$. The study revealed a strong temperature-dependent spectral evolution. Above 50 K, the low frequency optical conductivity is rather flat without a clear Drude-like response, indicating a very short transport life time of the free carriers. Well below the coherence temperature, there appears an abrupt spectral weight suppression below 400 cm$^{-1}$, yielding evidence for the formation of a hybridization energy gap arising from the mixing of the conduction electron and narrow f-electron bands. A small part of the suppressed spectral weight was transferred to the low frequency side, leading to a narrow Drude component, while the majority of the suppressed spectral weight was transferred to the high frequency side centered near 4000 cm$^{-1}$. Below the hidden order temperature, another very prominent energy gap structure was observed, which leads to the removal of a large part of the Drude component and a sharp reduction of the carrier scattering rate. The study revealed that the hybridization gap and the hidden orger gap are distinctly different: they occur at different energy scales and exhibit completely different spectral characteristics.Comment: 5 page

A Deep WSRT 1.4 GHz Radio Survey of the Spitzer Space Telescope FLSv Region

The First Look Survey (FLS) is the first scientific product to emerge from the Spitzer Space Telescope. A small region of this field (the verification strip) has been imaged very deeply, permitting the detection of cosmologically distant sources. We present Westerbork Synthesis Radio Telescope (WSRT) observations of this region, encompassing a ~1 sq. deg field, centred on the verification strip (J2000 RA=17:17:00.00, DEC=59:45:00.000). The radio images reach a noise level of ~ 8.5 microJy/beam - the deepest WSRT image made to date. We summarise here the first results from the project, and present the final mosaic image, together with a list of detected sources. The effect of source confusion on the position, size and flux density of the faintest sources in the source catalogue are also addressed. The results of a serendipitous search for HI emission in the field are also presented. Using a subset of the data, we clearly detect HI emission associated with four galaxies in the central region of the FLSv. These are identified with nearby, massive galaxies.Comment: 9 pages, 6 figures (fig.3 in a separate gif file). Accepted for publication in A&A. The full paper and the related material can be downloaded from http://www.astron.nl/wsrt/WSRTsurveys/WFLS